ERA5 Hourly - ECMWF Climate Reanalysis

Этот параметр представляет собой температуру, до которой необходимо охладить воздух на высоте 2 метров над поверхностью Земли для достижения состояния насыщения. Он является мерой влажности воздуха. В сочетании с температурой он может быть использован для расчета относительной влажности. Температура точки росы на высоте 2 метров рассчитывается путем интерполяции между самым низким уровнем модели и поверхностью Земли с учетом атмосферных условий.

Этот параметр представляет собой температуру воздуха на высоте 2 м над поверхностью суши, моря или внутренних водоемов. Температура на высоте 2 м рассчитывается путем интерполяции между самым низким уровнем модели и поверхностью Земли с учетом атмосферных условий.

Этот параметр представляет собой температуру морского льда в слое 1 (от 0 до 7 см). Интегрированная система прогнозирования (IFS) ЕЦСПП использует четырёхслойную морскую ледяную плиту: слой 1: 0–7 см, слой 2: 7–28 см, слой 3: 28–100 см, слой 4: 100–150 см. Температура морского льда в каждом слое изменяется в результате теплопередачи между слоями морского льда и атмосферой над ними, а также океаном под ними. Этот параметр определён для всего земного шара, даже там, где нет ни океана, ни морского льда. Регионы без морского льда можно замаскировать, рассматривая только те узлы сетки, где морской ледяной покров не имеет пропущенных значений и превышает 0,0.

Этот параметр представляет собой температуру морского льда во втором слое (7–28 см). Интегрированная система прогнозирования (IFS) ЕЦСПП использует четырёхслойную морскую ледяную плиту: слой 1: 0–7 см, слой 2: 7–28 см, слой 3: 28–100 см, слой 4: 100–150 см. Температура морского льда в каждом слое изменяется в результате теплопередачи между слоями морского льда и атмосферой над ними, а также океаном под ними. Этот параметр определён для всего земного шара, даже там, где нет ни океана, ни морского льда. Регионы без морского льда можно замаскировать, рассматривая только те узлы сетки, где морской ледяной покров не имеет пропущенных значений и превышает 0,0.

Этот параметр представляет собой температуру морского льда в слое 3 (28–100 см). Интегрированная система прогнозирования (IFS) ЕЦСПП использует четырёхслойную морскую ледяную плиту: слой 1: 0–7 см, слой 2: 7–28 см, слой 3: 28–100 см, слой 4: 100–150 см. Температура морского льда в каждом слое изменяется в результате теплопередачи между слоями морского льда и атмосферой над ними, а также океаном под ними. Этот параметр определён для всего земного шара, даже там, где нет ни океана, ни морского льда. Регионы без морского льда можно замаскировать, рассматривая только те узлы сетки, где морской ледяной покров не имеет пропущенных значений и превышает 0,0.

Этот параметр представляет собой температуру морского льда в слое 4 (100–150 см). Интегрированная система прогнозирования (IFS) ЕЦСПП использует четырёхслойную морскую ледяную плиту: слой 1: 0–7 см, слой 2: 7–28 см, слой 3: 28–100 см, слой 4: 100–150 см. Температура морского льда в каждом слое изменяется в результате теплопередачи между слоями морского льда и атмосферой над ними, а также океаном под ними. Этот параметр определён для всего земного шара, даже там, где нет ни океана, ни морского льда. Регионы без морского льда можно замаскировать, рассматривая только те узлы сетки, где морской ледяной покров не имеет пропущенных значений и превышает 0,0.

Этот параметр представляет собой давление (силу на единицу площади) атмосферы у поверхности Земли, скорректированное с учётом высоты среднего уровня моря. Он характеризует вес, который весь воздух в вертикальном столбе над точкой на поверхности Земли, если бы эта точка находилась на среднем уровне моря. Он рассчитывается для всех поверхностей – суши, моря и внутренних водоёмов. Карты среднего давления на уровне моря используются для определения местоположения погодных систем низкого и высокого давления, часто называемых циклонами и антициклонами. Контуры среднего давления на уровне моря также указывают на силу ветра. Плотные контуры соответствуют более сильным ветрам.

Этот параметр (SST) представляет собой температуру морской воды у поверхности. В ERA5 этот параметр является базовым SST, что означает отсутствие изменений, связанных с суточным циклом солнечной активности (суточными вариациями). SST в ERA5 предоставляется двумя внешними источниками. До сентября 2007 года использовались данные SST из набора данных HadISST2, а с сентября 2007 года — из набора данных OSTIA.

Этот параметр определяет температуру поверхности Земли. Температура поверхности Земли – это теоретическая температура, необходимая для поддержания баланса поверхностной энергии. Она представляет собой температуру самого верхнего слоя поверхности, который не обладает теплоёмкостью и поэтому может мгновенно реагировать на изменения поверхностных потоков. Температура поверхности Земли рассчитывается по-разному для суши и моря.

Этот параметр представляет собой давление (силу на единицу площади) атмосферы у поверхности суши, моря и внутренних водоёмов. Он является мерой веса всего воздуха в столбе над точкой на поверхности Земли. Приземное давление часто используется в сочетании с температурой для расчёта плотности воздуха. Сильные колебания давления с высотой затрудняют определение погодных систем низкого и высокого давления над горными районами, поэтому для этой цели обычно используется среднее давление на уровне моря, а не приземное давление.

Этот параметр представляет собой восточную составляющую ветра на высоте 100 м. Это горизонтальная скорость воздуха, движущегося на восток на высоте 100 м над поверхностью Земли, в метрах в секунду. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто локальны для конкретной точки пространства и времени, а не представляют собой усредненные значения по ячейке сетки модели. Этот параметр можно объединить с северной составляющей, чтобы получить скорость и направление горизонтального ветра на высоте 100 м.

Этот параметр представляет собой северную составляющую ветра на высоте 100 м. Это горизонтальная скорость воздуха, движущегося на север, на высоте 100 метров над поверхностью Земли, в метрах в секунду. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто локальны для конкретной точки пространства и времени, а не представляют собой усредненные значения по ячейке сетки модели. Этот параметр можно объединить с восточной составляющей, чтобы получить скорость и направление горизонтального ветра на высоте 100 м.

Этот параметр представляет собой восточную составляющую «нейтрального ветра» на высоте 10 метров над поверхностью Земли. Нейтральный ветер рассчитывается на основе поверхностного напряжения и соответствующей длины шероховатости, предполагая, что воздух нейтрально стратифицирован. В устойчивых условиях нейтральный ветер медленнее фактического, а в неустойчивых — быстрее. По определению, нейтральный ветер направлен в направлении поверхностного напряжения. Длина шероховатости зависит от свойств поверхности суши и состояния моря.

Этот параметр представляет собой восточную составляющую ветра на высоте 10 м. Это горизонтальная скорость воздуха, движущегося на восток на высоте 10 метров над поверхностью Земли, в метрах в секунду. Следует проявлять осторожность при сравнении этого параметра с данными наблюдений, поскольку данные наблюдений за ветром варьируются в малых пространственных и временных масштабах и зависят от особенностей рельефа местности, растительности и строений, которые представлены лишь в среднем в Интегрированной системе прогнозирования (IFS) ЕЦСПП. Этот параметр можно объединить с компонентой V ветра на высоте 10 м, чтобы получить скорость и направление горизонтального ветра на высоте 10 м.

Этот параметр представляет собой северную составляющую «нейтрального ветра» на высоте 10 метров над поверхностью Земли. Нейтральный ветер рассчитывается на основе поверхностного напряжения и соответствующей длины шероховатости, предполагая, что воздух нейтрально стратифицирован. Нейтральный ветер медленнее фактического ветра в стабильных условиях и быстрее в нестабильных. Нейтральный ветер, по определению, направлен в направлении поверхностного напряжения. Длина шероховатости зависит от свойств поверхности суши и состояния моря.

Этот параметр представляет собой северную составляющую ветра на высоте 10 м. Это горизонтальная скорость воздуха, движущегося на север на высоте 10 метров над поверхностью Земли, в метрах в секунду. Следует проявлять осторожность при сравнении этого параметра с данными наблюдений, поскольку данные наблюдений за ветром варьируются в малых пространственных и временных масштабах и зависят от особенностей рельефа местности, растительности и строений, которые представлены лишь в среднем в Интегрированной системе прогнозирования (IFS) ЕЦСПП. Этот параметр можно объединить с компонентой U ветра на высоте 10 м, чтобы получить скорость и направление горизонтального ветра на высоте 10 м.

Этот параметр представляет собой максимальный порыв ветра в указанное время на высоте десяти метров над поверхностью Земли. ВМО определяет порыв ветра как максимальную величину ветра, усредненную за трёхсекундные интервалы. Эта продолжительность короче шага модели, поэтому Интегрированная прогностическая система (IFS) ЕЦСПП вычисляет величину порыва в пределах каждого временного шага на основе усреднённых за этот временной шаг поверхностного напряжения, поверхностного трения, сдвига ветра и устойчивости. Следует проявлять осторожность при сравнении параметров модели с данными наблюдений, поскольку наблюдения часто локальны для конкретной точки пространства и времени, а не представляют собой усреднённые значения по ячейке сетки модели.

Этот параметр представляет собой среднюю скорость преобразования кинетической энергии в среднем потоке в тепло по всему атмосферному столбу на единицу площади, которая обусловлена ​​эффектами напряжения, связанного с турбулентными вихрями вблизи поверхности и турбулентным орографическим сопротивлением формы. Он рассчитывается с помощью схем турбулентной диффузии и турбулентного орографического сопротивления формы Интегрированной системы прогнозирования ЕЦСПП. Турбулентные вихри вблизи поверхности связаны с шероховатостью поверхности. Турбулентное орографическое сопротивление формы — это напряжение, вызванное долинами, холмами и горами на горизонтальных масштабах менее 5 км, которые определяются по данным о поверхности земли с разрешением около 1 км. (Диссипация, связанная с орографическими особенностями с горизонтальными масштабами между 5 км и масштабом сетки модели, учитывается схемой подсеточной орографии.) Этот параметр является средним за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидации. Для элементов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов, заканчивающихся на дату и время валидации.

Этот параметр представляет собой интенсивность осадков у поверхности Земли, которая рассчитывается схемой конвекции в Интегрированной системе прогнозирования (IFS) ЕЦСПП. Схема конвекции представляет конвекцию в пространственных масштабах, меньших, чем размер ячейки сетки. Осадки также могут быть рассчитаны схемой облачности в IFS, которая отображает образование и рассеивание облаков и крупномасштабных осадков из-за изменений атмосферных величин (таких как давление, температура и влажность), прогнозируемых непосредственно в пространственных масштабах ячейки сетки или больше. В IFS осадки состоят из дождя и снега. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидности. Для членов ансамбля, среднего по ансамблю и разброса ансамбля, период обработки составляет более 3 часов, заканчивающихся на дату и время валидности. Это интенсивность осадков, которая была бы, если бы они были равномерно распределены по ячейке сетки. 1 кг воды, разлитой на 1 квадратный метр поверхности, имеет глубину 1 мм (без учёта влияния температуры на плотность воды), поэтому единицы измерения эквивалентны мм (жидкой воды) в секунду. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто локальны для конкретной точки пространства и времени, а не представляют собой усреднённые значения по ячейке сетки модели.

Этот параметр представляет собой интенсивность снегопада на поверхности Земли, которая рассчитывается схемой конвекции в Интегрированной системе прогнозирования (IFS) ЕЦСПП. Схема конвекции представляет конвекцию в пространственных масштабах, меньших, чем размер ячейки сетки. Снегопад также может быть рассчитан схемой облачности в IFS, которая отображает образование и рассеивание облаков и крупномасштабных осадков из-за изменений атмосферных величин (таких как давление, температура и влажность), прогнозируемых непосредственно в пространственных масштабах ячейки сетки или больше. В IFS осадки состоят из дождя и снега. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидности. Для элементов ансамбля, среднего по ансамблю и разброса ансамбля, период обработки составляет более 3 часов, заканчивающихся на дату и время валидности. Это интенсивность снегопада, которая была бы равномерно распределена по ячейке сетки. Поскольку 1 кг воды, разлитой по поверхности 1 квадратный метр, имеет толщину 1 мм (без учёта влияния температуры на плотность воды), единицы измерения эквивалентны мм (жидкой воды) в секунду. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто локальны для конкретной точки пространства и времени, а не представляют собой усреднённые значения по ячейке сетки модели.

Обтекающий поверхность воздух создает напряжение (сопротивление), которое передает импульс поверхности и замедляет ветер. Этот параметр является компонентом среднего поверхностного напряжения в восточном направлении, связанным с низкоуровневыми орографическими блокирующими и орографическими гравитационными волнами. Он рассчитывается по схеме субсеточной орографии Интегрированной системы прогнозирования ЕЦСПП, которая представляет собой напряжение, вызванное неразрешенными долинами, холмами и горами с горизонтальными масштабами от 5 км до масштаба сетки модели. (Напряжение, связанное с орографическими особенностями с горизонтальными масштабами менее 5 км, учитывается схемой сопротивления турбулентной орографической формы). Орографические гравитационные волны представляют собой колебания потока, поддерживаемые плавучестью смещенных воздушных масс, возникающих при отклонении воздуха вверх холмами и горами. Этот процесс может создавать напряжение в атмосфере как у поверхности Земли, так и на других уровнях атмосферы. Положительные (отрицательные) значения указывают на напряжение на поверхности Земли в восточном (западном) направлении. Этот параметр представляет собой среднее значение за определённый период времени (период обработки), который зависит от извлечённых данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидации. Для членов ансамбля, среднего ансамбля и разброса ансамбля период обработки составляет более 3 часов, заканчивающихся на дату и время валидации.

Воздух, текущий над поверхностью, создает напряжение (сопротивление), которое передает импульс поверхности и замедляет ветер. Этот параметр является компонентом среднего поверхностного напряжения в восточном направлении, связанным с турбулентными вихрями вблизи поверхности и турбулентным орографическим сопротивлением формы. Он рассчитывается с помощью схем турбулентной диффузии и турбулентного орографического сопротивления формы Интегрированной системы прогнозирования ЕЦСПП. Турбулентные вихри вблизи поверхности связаны с шероховатостью поверхности. Турбулентное орографическое сопротивление формы — это напряжение, вызванное долинами, холмами и горами в горизонтальных масштабах менее 5 км, которые определяются по данным о поверхности Земли с разрешением около 1 км. (Напряжение, связанное с орографическими особенностями с горизонтальными масштабами между 5 км и масштабом сетки модели, учитывается схемой подсеточной орографической структуры.) Положительные (отрицательные) значения указывают на напряжение на поверхности Земли в восточном (западном) направлении. Этот параметр представляет собой среднее значение за определённый период времени (период обработки), который зависит от извлечённых данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидации. Для членов ансамбля, среднего ансамбля и разброса ансамбля период обработки составляет более 3 часов, заканчивающихся на дату и время валидации.

Этот параметр представляет собой количество воды, испарившейся с поверхности Земли, включая упрощенное представление транспирации (с растительности), в пар в воздухе над ней. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающийся на дату и время начала действия. Для элементов ансамбля, среднего значения ансамбля и разброса ансамбля, период обработки составляет более 3 часов, заканчивающийся на дату и время начала действия. Согласно правилам Интегрированной системы прогнозирования (IFS) ЕЦСПП, нисходящие потоки являются положительными. Поэтому отрицательные значения указывают на испарение, а положительные — на конденсацию.

Этот параметр представляет собой среднюю скорость преобразования кинетической энергии в среднем потоке в тепло по всему столбу атмосферы на единицу площади, обусловленную воздействием напряжений, связанных с орографическим блокированием на низком уровне и орографическими гравитационными волнами. Он рассчитывается по схеме подсеточной орографии Интегрированной системы прогнозирования ЕЦСПП, которая представляет собой напряжение, вызванное неразрешенными долинами, холмами и горами с горизонтальными масштабами от 5 км до масштаба сетки модели. (Диссипация, связанная с орографическими особенностями с горизонтальными масштабами менее 5 км, учитывается схемой турбулентного орографического сопротивления). Орографические гравитационные волны представляют собой колебания потока, поддерживаемые плавучестью смещенных воздушных масс, возникающих при отклонении воздуха вверх холмами и горами. Этот процесс может создавать напряжение в атмосфере как у поверхности Земли, так и на других уровнях атмосферы. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидации. Для элементов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов, заканчивающихся на дату и время валидации.

Этот параметр представляет собой среднее значение доли ячейки сетки (0-1), покрытой крупномасштабными осадками. Этот параметр представляет собой среднее значение за определённый период времени (период обработки), который зависит от извлечённых данных. Для повторного анализа период обработки составляет более 1 часа, заканчиваясь на дату и время валидации. Для членов ансамбля, среднего ансамбля и разброса ансамбля период обработки составляет более 3 часов, заканчиваясь на дату и время валидации.

Этот параметр представляет собой интенсивность осадков у поверхности Земли, которая генерируется схемой облачности в Интегрированной системе прогнозирования (IFS) ЕЦСПП. Схема облачности отображает образование и рассеивание облаков и крупномасштабных осадков из-за изменений атмосферных величин (таких как давление, температура и влажность), прогнозируемых непосредственно в пространственных масштабах ячейки сетки или больше. Осадки также могут быть сгенерированы схемой конвекции в IFS, которая отображает конвекцию в пространственных масштабах, меньших ячейки сетки. В IFS осадки состоят из дождя и снега. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидности. Для членов ансамбля, среднего по ансамблю и разброса по ансамблю, период обработки составляет более 3 часов, заканчивающихся на дату и время валидности. Это интенсивность осадков, которая была бы, если бы они были равномерно распределены по ячейке сетки. Поскольку 1 кг воды, разлитой на 1 квадратный метр поверхности, имеет глубину 1 мм (без учёта влияния температуры на плотность воды), единицы измерения эквивалентны мм (жидкой воды) в секунду. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто локальны для конкретной точки пространства и времени, а не представляют собой усреднённые значения по ячейке сетки модели.

Этот параметр представляет собой интенсивность снегопада у поверхности Земли, которая рассчитывается схемой облачности в Интегрированной системе прогнозирования (IFS) ЕЦСПП. Схема облачности отображает образование и рассеивание облаков и крупномасштабных осадков из-за изменений атмосферных величин (таких как давление, температура и влажность), прогнозируемых непосредственно в пространственных масштабах ячейки сетки или больше. Снегопад также может быть рассчитан схемой конвекции в IFS, которая отображает конвекцию в пространственных масштабах, меньших ячейки сетки. В IFS осадки состоят из дождя и снега. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидности. Для элементов ансамбля, среднего по ансамблю и разброса ансамбля, период обработки составляет более 3 часов, заканчивающихся на дату и время валидности. Это интенсивность снегопада, которая была бы равномерно распределена по ячейке сетки. Поскольку 1 кг воды, разлитой на 1 квадратный метр поверхности, имеет глубину 1 мм (без учёта влияния температуры на плотность воды), единицы измерения эквивалентны мм (жидкой воды) в секунду. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто локальны для конкретной точки пространства и времени, а не представляют собой усреднённые значения по ячейке сетки модели.

Обтекающий поверхность воздух создает напряжение (сопротивление), которое передает импульс поверхности и замедляет ветер. Этот параметр является компонентом среднего поверхностного напряжения в северном направлении, связанным с низкоуровневыми орографическими блокирующими и орографическими гравитационными волнами. Он рассчитывается по схеме субсеточной орографии Интегрированной системы прогнозирования ЕЦСПП, которая представляет собой напряжение, вызванное неразрешенными долинами, холмами и горами с горизонтальными масштабами от 5 км до масштаба сетки модели. (Напряжение, связанное с орографическими особенностями с горизонтальными масштабами менее 5 км, учитывается схемой сопротивления турбулентной орографической формы). Орографические гравитационные волны представляют собой колебания потока, поддерживаемые плавучестью смещенных воздушных масс, возникающих при отклонении воздуха вверх холмами и горами. Этот процесс может создавать напряжение в атмосфере у поверхности Земли и на других уровнях атмосферы. Положительные (отрицательные) значения указывают на напряжение на поверхности Земли в направлении на север (юг). Этот параметр представляет собой среднее значение за определённый период времени (период обработки), который зависит от извлечённых данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидации. Для членов ансамбля, среднего ансамбля и разброса ансамбля период обработки составляет более 3 часов, заканчивающихся на дату и время валидации.

Воздух, текущий над поверхностью, создает напряжение (сопротивление), которое передает импульс поверхности и замедляет ветер. Этот параметр является компонентом среднего поверхностного напряжения в северном направлении, связанным с турбулентными вихрями вблизи поверхности и турбулентным орографическим сопротивлением формы. Он рассчитывается с помощью схем турбулентной диффузии и турбулентного орографического сопротивления формы Интегрированной системы прогнозирования ЕЦСПП. Турбулентные вихри вблизи поверхности связаны с шероховатостью поверхности. Турбулентное орографическое сопротивление формы — это напряжение, вызванное долинами, холмами и горами в горизонтальных масштабах менее 5 км, которые определяются по данным о поверхности Земли с разрешением около 1 км. (Напряжение, связанное с орографическими особенностями с горизонтальными масштабами между 5 км и масштабом сетки модели, учитывается схемой подсеточной орографической формы.) Положительные (отрицательные) значения указывают на напряжение на поверхности Земли в северном (южном) направлении. Этот параметр представляет собой среднее значение за определённый период времени (период обработки), который зависит от извлечённых данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидации. Для членов ансамбля, среднего ансамбля и разброса ансамбля период обработки составляет более 3 часов, заканчивающихся на дату и время валидации.

Этот параметр является мерой того, в какой степени приземные атмосферные условия способствуют испарению. Обычно под ним понимается количество испарения при существующих атмосферных условиях с поверхности чистой воды, имеющей температуру самого нижнего слоя атмосферы, что позволяет оценить максимально возможное испарение. В современной Интегрированной системе прогнозирования (IFS) ЕЦСПП расчет потенциального испарения основан на расчетах баланса поверхностной энергии с параметрами растительности, заданными как «сельскохозяйственные культуры/смешанное земледелие», и предполагается, что «нет стресса от почвенной влаги». Другими словами, испарение для сельскохозяйственных угодий рассчитывается как хорошо орошаемое, и предполагается, что атмосфера не подвержена влиянию этого искусственного состояния поверхности. Последнее не всегда соответствует действительности. Хотя потенциальное испарение предназначено для оценки потребности в орошении, этот метод может давать нереалистичные результаты в засушливых условиях из-за слишком интенсивного испарения, вызванного сухим воздухом. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающегося на дату и время валидации. Для элементов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов, заканчивающихся на дату и время валидации.

Некоторое количество воды из осадков, таяния снега или глубоко в почве остается в почве. В противном случае вода стекает либо по поверхности (поверхностный сток), либо под землю (подземный сток), и сумма этих двух параметров называется стоком. Этот параметр является средним значением за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающийся на дату и время валидности. Для членов ансамбля, среднего по ансамблю и рассеяния ансамбля, период обработки составляет более 3 часов, заканчивающийся на дату и время валидности. Это скорость стока, если бы он был равномерно распределен по ячейке сетки. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто являются локальными для конкретной точки, а не усредненными по ячейке сетки. Сток является мерой доступности воды в почве и может, например, использоваться в качестве индикатора засухи или наводнения.

Этот параметр представляет собой среднюю скорость испарения снега с покрытой снегом области ячейки сетки в пар в воздухе над ней. Интегрированная система прогнозирования (IFS) ЕЦСПП представляет снег как один дополнительный слой над самым верхним уровнем почвы. Снег может покрывать всю ячейку сетки или ее часть. Этот параметр является средним значением за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающийся на дату и время достоверности. Для членов ансамбля, среднего по ансамблю и рассеяния по ансамблю, период обработки составляет более 3 часов, заканчивающийся на дату и время достоверности. Это скорость испарения снега, если бы он был равномерно распределен по ячейке сетки. 1 кг воды, распределенной по 1 квадратному метру поверхности, составляет 1 мм глубиной (без учета влияния температуры на плотность воды), поэтому единицы эквивалентны мм (жидкой воды) в секунду. Соглашение IFS заключается в том, что нисходящие потоки положительны. Таким образом, отрицательные значения указывают на испарение, а положительные значения — на осаждение.

Этот параметр представляет собой интенсивность снегопада у поверхности Земли. Он представляет собой сумму крупномасштабных и конвективных снегопадов. Крупномасштабные снегопады генерируются схемой облачности в Интегрированной системе прогнозирования (IFS) ЕЦСПП. Схема облачности отображает образование и рассеивание облаков и крупномасштабных осадков из-за изменений атмосферных величин (таких как давление, температура и влажность), прогнозируемых непосредственно в пространственных масштабах ячейки сетки или больше. Конвективные снегопады генерируются схемой конвекции в IFS, которая отображает конвекцию в пространственных масштабах, меньших ячейки сетки. В IFS осадки состоят из дождя и снега. Этот параметр является средним значением за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчиваясь на дату и время достоверности. Для членов ансамбля, среднего по ансамблю и разброса по ансамблю период обработки составляет более 3 часов, заканчиваясь на дату и время достоверности. Это интенсивность снегопада, равномерно распределенного по ячейке сетки. 1 кг воды, распределенной по 1 квадратному метру поверхности, имеет толщину 1 мм (без учета влияния температуры на плотность воды), поэтому единицы измерения эквивалентны мм (жидкой воды) в секунду. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто локальны для конкретной точки пространства и времени, а не представляют собой усредненные значения по ячейке сетки модели.

Этот параметр представляет собой скорость таяния снега в покрытой снегом области ячейки сетки. Интегрированная система прогнозирования ECMWF (IFS) представляет снег как один дополнительный слой над самым верхним уровнем почвы. Снег может покрывать всю ячейку сетки или ее часть. Этот параметр является средним значением за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки составляет более 1 часа, заканчивающийся на дату и время достоверности. Для членов ансамбля, среднего по ансамблю и разброса по ансамблю, период обработки составляет более 3 часов, заканчивающийся на дату и время достоверности. Это скорость таяния, если бы она была равномерно распределена по ячейке сетки. 1 кг воды, разлитой по 1 квадратному метру поверхности, имеет глубину 1 мм (без учета влияния температуры на плотность воды), поэтому единицы эквивалентны мм (жидкой воды) в секунду.

Некоторое количество воды из осадков, таяния снега или глубоко в почве остается в почве. В противном случае вода стекает либо по поверхности (поверхностный сток), либо под землю (подземный сток), и сумма этих двух факторов называется стоком. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Это скорость стока, если бы он был равномерно распределен по сетке. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто являются локальными для конкретной точки, а не усредняются по сетке. Сток является мерой наличия воды в почве и может, например, использоваться как индикатор засухи или наводнения.

Этот параметр представляет собой количество прямой солнечной радиации (также известной как коротковолновая радиация), достигающей поверхности Земли. Это количество излучения, проходящего через горизонтальную плоскость. Солнечное излучение на поверхности может быть прямым или рассеянным. Солнечное излучение может рассеиваться во всех направлениях частицами атмосферы, часть из которых достигает поверхности (диффузное солнечное излучение). Некоторая часть солнечной радиации достигает поверхности, не рассеиваясь (прямое солнечное излучение). Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой количество прямой радиации Солнца (также известной как солнечная или коротковолновая радиация), достигающей поверхности Земли при условии ясного неба (безоблачности). Это количество излучения, проходящего через горизонтальную плоскость. Солнечное излучение на поверхности может быть прямым или рассеянным. Солнечное излучение может рассеиваться во всех направлениях частицами атмосферы, часть из которых достигает поверхности (диффузное солнечное излучение). Некоторая часть солнечной радиации достигает поверхности, не рассеиваясь (прямое солнечное излучение). Количество радиации ясного неба рассчитывается для тех же атмосферных условий (температура, влажность, озон, примеси газов и аэрозоли), что и соответствующие количества всего неба (включая облака), но при условии, что облаков нет. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Соглашение ECMWF для вертикальных потоков положительно в направлении вниз.

Этот параметр представляет собой количество теплового (также известного как длинноволновое или земное) излучения, испускаемого атмосферой и облаками, которое достигает горизонтальной плоскости на поверхности Земли. Поверхность Земли излучает тепловое излучение, часть которого поглощается атмосферой и облаками. Атмосфера и облака также излучают тепловое излучение во всех направлениях, часть которого достигает поверхности (представленной этим параметром). Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой количество теплового (также известного как длинноволновое или земное) излучения, испускаемого атмосферой, которое достигает горизонтальной плоскости на поверхности Земли при условии ясного (безоблачного) неба. Поверхность Земли излучает тепловое излучение, часть которого поглощается атмосферой и облаками. Атмосфера и облака также излучают тепловое излучение во всех направлениях, часть которого достигает поверхности. Количество радиации ясного неба рассчитывается для тех же атмосферных условий (температура, влажность, озон, примеси газов и аэрозоли), что и соответствующие количества всего неба (включая облака), но при условии, что облаков нет. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой количество солнечной радиации (также известной как коротковолновая радиация), которая достигает горизонтальной плоскости на поверхности Земли. Этот параметр включает в себя как прямую, так и рассеянную солнечную радиацию. Излучение Солнца (солнечное или коротковолновое излучение) частично отражается обратно в космос облаками и частицами в атмосфере (аэрозоли), а часть поглощается. Остальное происходит на поверхности Земли (представлено этим параметром). В достаточно хорошем приближении этот параметр является модельным эквивалентом того, что можно было бы измерить пиранометром (прибором, используемым для измерения солнечной радиации) на поверхности. Однако следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто являются локальными для определенной точки пространства и времени, а не представляют собой средние значения по сетке модели. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой количество солнечной радиации (также известной как коротковолновая радиация), которая достигает горизонтальной плоскости на поверхности Земли при условии ясного неба (безоблачности). Этот параметр включает в себя как прямую, так и рассеянную солнечную радиацию. Излучение Солнца (солнечное или коротковолновое излучение) частично отражается обратно в космос облаками и частицами в атмосфере (аэрозоли), а часть поглощается. Остальное происходит на поверхности Земли. Количество радиации ясного неба рассчитывается для тех же атмосферных условий (температура, влажность, озон, примеси газов и аэрозоли), что и соответствующие количества всего неба (включая облака), но при условии, что облаков нет. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Соглашение ECMWF для вертикальных потоков положительно в направлении вниз.

Этот параметр представляет собой количество ультрафиолетового (УФ) излучения, достигающего поверхности. Это количество излучения, проходящего через горизонтальную плоскость. УФ-излучение — это часть электромагнитного спектра, излучаемого Солнцем, длина волны которого короче видимого света. В системе интегрированного прогнозирования ЕЦСПП (IFS) оно определяется как излучение с длиной волны 0,20–0,44 мкм (микрон, 1 миллионная метра). Небольшое количество ультрафиолета необходимо живым организмам, но чрезмерное воздействие может привести к повреждению клеток; у людей это включает острые и хронические последствия для здоровья кожи, глаз и иммунной системы. УФ-излучение поглощается озоновым слоем, но часть достигает поверхности. Истощение озонового слоя вызывает обеспокоенность по поводу увеличения разрушительного воздействия ультрафиолета. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой передачу скрытого тепла (в результате фазовых изменений воды, таких как испарение или конденсация) между поверхностью Земли и атмосферой за счет эффектов турбулентного движения воздуха. Испарение с поверхности Земли представляет собой передачу энергии с поверхности в атмосферу. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Тепловое излучение (также известное как длинноволновое или земное излучение) относится к излучению, испускаемому атмосферой, облаками и поверхностью Земли. Этот параметр представляет собой разницу между нисходящим и восходящим тепловым излучением на поверхности Земли. Это количество излучения, проходящего через горизонтальную плоскость. Атмосфера и облака испускают тепловое излучение во всех направлениях, часть которого достигает поверхности в виде нисходящего теплового излучения. Восходящее тепловое излучение на поверхности состоит из теплового излучения, испускаемого поверхностью, плюс доля нисходящего теплового излучения, отраженного поверхностью вверх. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Тепловое излучение (также известное как длинноволновое или земное излучение) относится к излучению, испускаемому атмосферой, облаками и поверхностью Земли. Этот параметр представляет собой разницу между нисходящим и восходящим тепловым излучением на поверхности Земли при условии ясного неба (безоблачности). Это количество излучения, проходящего через горизонтальную плоскость. Количество радиации ясного неба рассчитывается для тех же атмосферных условий (температура, влажность, озон, примеси газов и аэрозоли), что и соответствующие количества всего неба (включая облака), но при условии, что облаков нет. Атмосфера и облака испускают тепловое излучение во всех направлениях, часть которого достигает поверхности в виде нисходящего теплового излучения. Восходящее тепловое излучение на поверхности состоит из теплового излучения, испускаемого поверхностью, плюс доля нисходящего теплового излучения, отраженного поверхностью вверх. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой количество солнечного излучения (также известного как коротковолновое излучение), которое достигает горизонтальной плоскости на поверхности Земли (как прямого, так и рассеянного), за вычетом количества, отраженного поверхностью Земли (которое определяется альбедо). Излучение Солнца (солнечное или коротковолновое излучение) частично отражается обратно в космос облаками и частицами в атмосфере (аэрозоли), а часть поглощается. Остальная часть попадает на поверхность Земли, где часть ее отражается. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой количество солнечной (коротковолновой) радиации, достигающей поверхности Земли (как прямой, так и рассеянной), за вычетом количества, отраженного поверхностью Земли (которое определяется альбедо), при условии ясного неба (безоблачности). Это количество излучения, проходящего через горизонтальную плоскость. Количество радиации ясного неба рассчитывается для тех же атмосферных условий (температура, влажность, озон, примеси газов и аэрозоли), что и соответствующие количества всего неба (включая облака), но при условии, что облаков нет. Излучение Солнца (солнечное или коротковолновое излучение) частично отражается обратно в космос облаками и частицами в атмосфере (аэрозоли), а часть поглощается. Остальное попадает на поверхность Земли, где часть его отражается. Разница между нисходящей и отраженной солнечной радиацией представляет собой чистую солнечную радиацию на поверхности. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Некоторое количество воды из осадков, таяния снега или глубоко в почве остается в почве. В противном случае вода стекает либо по поверхности (поверхностный сток), либо под землю (подземный сток), и сумма этих двух факторов называется стоком. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Это скорость стока, если бы он был равномерно распределен по сетке. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто являются локальными для конкретной точки, а не усредняются по сетке. Сток является мерой наличия воды в почве и может, например, использоваться как индикатор засухи или наводнения.

Этот параметр представляет собой передачу тепла между поверхностью Земли и атмосферой за счет эффектов турбулентного движения воздуха (но исключая любую передачу тепла в результате конденсации или испарения). Величина явного теплового потока определяется разницей температур между поверхностью и вышележащей атмосферой, скоростью ветра и шероховатостью поверхности. Например, холодный воздух, покрывающий теплую поверхность, будет вызывать ощутимый поток тепла от суши (или океана) в атмосферу. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой поступающую солнечную радиацию (также известную как коротковолновая радиация), полученную от Солнца в верхних слоях атмосферы. Это количество излучения, проходящего через горизонтальную плоскость. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Тепловое (также известное как земное или длинноволновое) излучение, испускаемое в космос в верхних слоях атмосферы, широко известно как исходящее длинноволновое излучение (OLR). Верхнее чистое тепловое излучение (этот параметр) равно отрицательному значению OLR. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой тепловое (также известное как земное или длинноволновое) излучение, испускаемое в космос в верхних слоях атмосферы при условии ясного неба (безоблачности). Это количество, проходящее через горизонтальную плоскость. Обратите внимание, что соглашение ECMWF для вертикальных потоков является положительным вниз, поэтому поток из атмосферы в космос будет отрицательным. Количество радиации ясного неба рассчитывается для точно тех же атмосферных условий (температура, влажность, озон, примеси газов и аэрозоли), что и количества всего неба (включая облака), но при условии, что облаков нет. Тепловое излучение, испускаемое в космос в верхних слоях атмосферы, широко известно как уходящая длинноволновая радиация (OLR) (т. е. поток из атмосферы в космос считается положительным). Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия.

Этот параметр представляет собой приходящую солнечную радиацию (также известную как коротковолновая радиация) минус исходящую солнечную радиацию в верхних слоях атмосферы. Это количество излучения, проходящего через горизонтальную плоскость. Приходящая солнечная радиация – это количество, полученное от Солнца. Исходящая солнечная радиация – это количество отраженной и рассеянной атмосферой и поверхностью Земли. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой пришедшую солнечную радиацию (также известную как коротковолновая радиация) минус исходящую солнечную радиацию в верхних слоях атмосферы при условии ясного неба (безоблачности). Это количество излучения, проходящего через горизонтальную плоскость. Приходящая солнечная радиация – это количество, полученное от Солнца. Исходящая солнечная радиация – это количество отраженной и рассеянной атмосферой и поверхностью Земли при условии ясного неба (безоблачности). Количество радиации ясного неба рассчитывается для точно тех же атмосферных условий (температура, влажность, озон, примеси газов и аэрозоли), что и количества всего неба (включая облака), но при условии, что облаков нет. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Соглашение ECMWF для вертикальных потоков положительно в направлении вниз.

Этот параметр представляет собой скорость выпадения осадков на поверхности Земли. Это сумма ставок крупномасштабных осадков и конвективных осадков. Крупномасштабные осадки генерируются облачной схемой Интегрированной системы прогнозирования (IFS) ЕЦСПП. Схема облаков представляет собой образование и рассеивание облаков и крупномасштабных осадков из-за изменений атмосферных величин (таких как давление, температура и влажность), прогнозируемых непосредственно в пространственных масштабах ячейки сетки или более крупных. Конвективные осадки генерируются схемой конвекции в IFS, которая представляет конвекцию в пространственных масштабах, меньших, чем ячейка сетки. В IFS осадки состоят из дождя и снега. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Это скорость выпадения осадков, если бы они были равномерно распределены по сетке. 1 кг воды, распределенной на 1 квадратный метр поверхности, имеет глубину 1 мм (без учета влияния температуры на плотность воды), поэтому единицы измерения эквивалентны мм (жидкой воды) в секунду. Следует проявлять осторожность при сравнении параметров модели с наблюдениями, поскольку наблюдения часто являются локальными для определенной точки пространства и времени, а не представляют собой средние значения по сетке модели.

Вертикальный интеграл потока влаги представляет собой горизонтальную скорость потока влаги (водяного пара, облачной жидкости и облачного льда) на метр поперечного потока для столба воздуха, простирающегося от поверхности Земли до верхних слоев атмосферы. Его горизонтальное расхождение — это скорость распространения влаги наружу от точки на квадратный метр. Этот параметр представляет собой среднее значение за определенный период времени (период обработки), который зависит от извлеченных данных. Для повторного анализа период обработки превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период обработки составляет более 3 часов и заканчивается в дату и время действия. Этот параметр положителен для влаги, которая распространяется, или расходится, и отрицателен, наоборот, для влаги, которая концентрируется, или сближается (конвергенция). Таким образом, этот параметр указывает, приводят ли атмосферные движения к уменьшению (для дивергенции) или увеличению (для конвергенции) вертикального интеграла влажности за определенный период времени. Высокие отрицательные значения этого параметра (т.е. большая конвергенция влажности) могут быть связаны с усилением осадков и наводнениями. 1 кг воды, распределенной на 1 квадратный метр поверхности, имеет глубину 1 мм (без учета влияния температуры на плотность воды), поэтому единицы измерения эквивалентны мм (жидкой воды) в секунду.

Этот параметр представляет собой количество прямой радиации Солнца (также известной как солнечная или коротковолновая радиация), достигающей поверхности Земли при условии ясного неба (безоблачности). Это количество излучения, проходящего через горизонтальную плоскость. Солнечное излучение на поверхности может быть прямым или рассеянным. Солнечное излучение может рассеиваться во всех направлениях частицами атмосферы, часть из которых достигает поверхности (диффузное солнечное излучение). Некоторая часть солнечной радиации достигает поверхности, не рассеиваясь (прямое солнечное излучение). Количество радиации ясного неба рассчитывается для тех же атмосферных условий (температура, влажность, озон, примеси газов и аэрозоли), что и соответствующие количества всего неба (включая облака), но при условии, что облаков нет. Этот параметр накапливается за определенный период времени, который зависит от извлеченных данных. Для повторного анализа период накопления превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период накопления составляет более 3 часов и заканчивается в дату и время действия. Единицы измерения — джоули на квадратный метр (Дж м^-2). Для перевода в ватты на квадратный метр (Вт·м^-2) накопленные значения следует разделить на период накопления, выраженный в секундах. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой количество ультрафиолетового (УФ) излучения, достигающего поверхности. Это количество излучения, проходящего через горизонтальную плоскость. УФ-излучение — это часть электромагнитного спектра, излучаемого Солнцем, длина волны которого короче видимого света. В системе интегрированного прогнозирования ЕЦСПП (IFS) оно определяется как излучение с длиной волны 0,20–0,44 мкм (микрон, 1 миллионная метра). Небольшое количество ультрафиолета необходимо живым организмам, но чрезмерное воздействие может привести к повреждению клеток; у людей это включает острые и хронические последствия для здоровья кожи, глаз и иммунной системы. УФ-излучение поглощается озоновым слоем, но часть достигает поверхности. Истощение озонового слоя вызывает обеспокоенность по поводу увеличения разрушительного воздействия ультрафиолета. Этот параметр накапливается за определенный период времени, который зависит от извлеченных данных. Для повторного анализа период накопления превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период накопления составляет более 3 часов и заканчивается в дату и время действия. Единицы измерения — джоули на квадратный метр (Дж м^-2). Для перевода в ватты на квадратный метр (Вт·м^-2) накопленные значения следует разделить на период накопления, выраженный в секундах. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой натуральный логарифм длины шероховатости для нагрева. Шероховатость поверхности для нагрева является мерой поверхностного сопротивления теплопередаче. Этот параметр используется для определения передачи тепла от воздуха к поверхности. Для данных атмосферных условий более высокая шероховатость поверхности для тепла означает, что воздуху труднее обмениваться теплом с поверхностью. Меньшая шероховатость поверхности для тепла означает, что воздуху легче обмениваться теплом с поверхностью. Над океаном шероховатость поверхности для тепла зависит от волн. Над морским льдом она имеет постоянное значение 0,001 м. На суше он зависит от типа растительности и снежного покрова.

Этот параметр представляет собой передачу тепла между поверхностью Земли и атмосферой в указанное время за счет эффектов турбулентного движения воздуха (но исключая любую передачу тепла в результате конденсации или испарения). Величина явного теплового потока определяется разницей температур между поверхностью и вышележащей атмосферой, скоростью ветра и шероховатостью поверхности. Например, холодный воздух, покрывающий теплую поверхность, будет вызывать ощутимый поток тепла от суши (или океана) в атмосферу. Конвенция ECMWF для вертикальных потоков положительна вниз.

Альбедо — это мера отражательной способности поверхности Земли. Этот параметр представляет собой долю рассеянного солнечного (коротковолнового) излучения с длинами волн от 0,7 до 4 мкм (микронов, 1 миллионная часть метра), отраженного поверхностью Земли (только для незаснеженных поверхностей суши). Значения этого параметра варьируются от 0 до 1. В Интегрированной системе прогнозирования ЕЦСПП (IFS) альбедо рассматривается отдельно для солнечного излучения с длиной волны больше/меньше 0,7 мкм, а также для прямого и рассеянного солнечного излучения (что дает альбедо 4 компонента). Солнечное излучение на поверхности может быть прямым или рассеянным. Солнечное излучение может рассеиваться во всех направлениях частицами атмосферы, часть из которых достигает поверхности (диффузное солнечное излучение). Некоторая часть солнечной радиации достигает поверхности, не рассеиваясь (прямое солнечное излучение). В IFS используется климатологическое (наблюдаемые значения, усредненные за период в несколько лет) фоновое альбедо, которое меняется от месяца к месяцу в течение года и модифицируется моделью по воде, льду и снегу.

Альбедо — это мера отражательной способности поверхности Земли. Этот параметр представляет собой долю прямого солнечного (коротковолнового) излучения с длинами волн от 0,7 до 4 мкм (микрон, 1 миллионная доля метра), отраженного поверхностью Земли (только для незаснеженных поверхностей суши). Значения этого параметра варьируются от 0 до 1. В Интегрированной системе прогнозирования ЕЦСПП (IFS) альбедо рассматривается отдельно для солнечного излучения с длиной волны больше/меньше 0,7 мкм, а также для прямого и рассеянного солнечного излучения (что дает альбедо 4 компонента). Солнечное излучение на поверхности может быть прямым или рассеянным. Солнечное излучение может рассеиваться во всех направлениях частицами атмосферы, часть из которых достигает поверхности (диффузное солнечное излучение). Некоторая часть солнечной радиации достигает поверхности, не рассеиваясь (прямое солнечное излучение). В IFS используется климатологическое (наблюдаемые значения, усредненные за период в несколько лет) фоновое альбедо, которое меняется от месяца к месяцу в течение года и модифицируется моделью по воде, льду и снегу.

Этот параметр представляет собой передачу скрытого тепла (в результате фазовых изменений воды, таких как испарение или конденсация) между поверхностью Земли и атмосферой за счет эффектов турбулентного движения воздуха. Испарение с поверхности Земли представляет собой передачу энергии с поверхности в атмосферу. Этот параметр накапливается за определенный период времени, который зависит от извлеченных данных. Для повторного анализа период накопления превышает 1 час и заканчивается в дату и время действия. Для членов ансамбля, среднего значения ансамбля и разброса ансамбля период накопления составляет более 3 часов и заканчивается в дату и время действия. Единицы измерения — джоули на квадратный метр (Дж м^-2). Для перевода в ватты на квадратный метр (Вт·м^-2) накопленные значения следует разделить на период накопления, выраженный в секундах. Конвенция ECMWF для вертикальных потоков положительна вниз.

Этот параметр представляет собой количество солнечного излучения (также известного как коротковолновое излучение), которое достигает горизонтальной плоскости на поверхности Земли (как прямого, так и рассеянного), за вычетом количества, отраженного поверхностью Земли (которое определяется альбедо). Излучение Солнца (солнечное или коротковолновое излучение) частично отражается обратно в космос облаками и частицами в атмосфере (аэрозоли), а часть поглощается. Остальное попадает на поверхность Земли, где часть его отражается. Этот параметр накапливается за определенный период времени, который зависит от извлеченных данных. Для повторного анализа период накопления превышает 1 час и заканчивается в дату и время действия. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. Соглашение ECMWF для вертикальных потоков положительно в направлении вниз.

This parameter is the amount of solar (shortwave) radiation reaching the surface of the Earth (both direct and diffuse) minus the amount reflected by the Earth's surface (which is governed by the albedo), assuming clear-sky (cloudless) conditions. It is the amount of radiation passing through a horizontal plane. Clear-sky radiation quantities are computed for exactly the same atmospheric conditions of temperature, humidity, ozone, trace gases and aerosol as the corresponding total-sky quantities (clouds included), but assuming that the clouds are not there. Radiation from the Sun (solar, or shortwave, radiation) is partly reflected back to space by clouds and particles in the atmosphere (aerosols) and some of it is absorbed. The rest is incident on the Earth's surface, where some of it is reflected. The difference between downward and reflected solar radiation is the surface net solar radiation. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

Thermal radiation (also known as longwave or terrestrial radiation) refers to radiation emitted by the atmosphere, clouds and the surface of the Earth. This parameter is the difference between downward and upward thermal radiation at the surface of the Earth. It is the amount of radiation passing through a horizontal plane. The atmosphere and clouds emit thermal radiation in all directions, some of which reaches the surface as downward thermal radiation. The upward thermal radiation at the surface consists of thermal radiation emitted by the surface plus the fraction of downwards thermal radiation reflected upward by the surface. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. Соглашение ECMWF для вертикальных потоков положительно в направлении вниз.

Thermal radiation (also known as longwave or terrestrial radiation) refers to radiation emitted by the atmosphere, clouds and the surface of the Earth. This parameter is the difference between downward and upward thermal radiation at the surface of the Earth, assuming clear-sky (cloudless) conditions. It is the amount of radiation passing through a horizontal plane. Clear-sky radiation quantities are computed for exactly the same atmospheric conditions of temperature, humidity, ozone, trace gases and aerosol as the corresponding total-sky quantities (clouds included), but assuming that the clouds are not there. The atmosphere and clouds emit thermal radiation in all directions, some of which reaches the surface as downward thermal radiation. The upward thermal radiation at the surface consists of thermal radiation emitted by the surface plus the fraction of downwards thermal radiation reflected upward by the surface. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

This parameter is the transfer of heat between the Earth's surface and the atmosphere through the effects of turbulent air motion (but excluding any heat transfer resulting from condensation or evaporation). The magnitude of the sensible heat flux is governed by the difference in temperature between the surface and the overlying atmosphere, wind speed and the surface roughness. For example, cold air overlying a warm surface would produce a sensible heat flux from the land (or ocean) into the atmosphere. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. Соглашение ECMWF для вертикальных потоков положительно в направлении вниз.

This parameter is the amount of solar radiation (also known as shortwave radiation) that reaches a horizontal plane at the surface of the Earth, assuming clear-sky (cloudless) conditions. This parameter comprises both direct and diffuse solar radiation. Radiation from the Sun (solar, or shortwave, radiation) is partly reflected back to space by clouds and particles in the atmosphere (aerosols) and some of it is absorbed. The rest is incident on the Earth's surface. Clear-sky radiation quantities are computed for exactly the same atmospheric conditions of temperature, humidity, ozone, trace gases and aerosol as the corresponding total-sky quantities (clouds included), but assuming that the clouds are not there. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

This parameter is the amount of solar radiation (also known as shortwave radiation) that reaches a horizontal plane at the surface of the Earth. This parameter comprises both direct and diffuse solar radiation. Radiation from the Sun (solar, or shortwave, radiation) is partly reflected back to space by clouds and particles in the atmosphere (aerosols) and some of it is absorbed. The rest is incident on the Earth's surface (represented by this parameter). To a reasonably good approximation, this parameter is the model equivalent of what would be measured by a pyranometer (an instrument used for measuring solar radiation) at the surface. However, care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

This parameter is the amount of thermal (also known as longwave or terrestrial) radiation emitted by the atmosphere that reaches a horizontal plane at the surface of the Earth, assuming clear-sky (cloudless) conditions. The surface of the Earth emits thermal radiation, some of which is absorbed by the atmosphere and clouds. The atmosphere and clouds likewise emit thermal radiation in all directions, some of which reaches the surface. Clear-sky radiation quantities are computed for exactly the same atmospheric conditions of temperature, humidity, ozone, trace gases and aerosol as the corresponding total-sky quantities (clouds included), but assuming that the clouds are not there. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

This parameter is the amount of thermal (also known as longwave or terrestrial) radiation emitted by the atmosphere and clouds that reaches a horizontal plane at the surface of the Earth. The surface of the Earth emits thermal radiation, some of which is absorbed by the atmosphere and clouds. The atmosphere and clouds likewise emit thermal radiation in all directions, some of which reaches the surface (represented by this parameter). This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

This parameter is the incoming solar radiation (also known as shortwave radiation), received from the Sun, at the top of the atmosphere. It is the amount of radiation passing through a horizontal plane. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

This parameter is the incoming solar radiation (also known as shortwave radiation) minus the outgoing solar radiation at the top of the atmosphere. It is the amount of radiation passing through a horizontal plane. The incoming solar radiation is the amount received from the Sun. The outgoing solar radiation is the amount reflected and scattered by the Earth's atmosphere and surface. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

This parameter is the incoming solar radiation (also known as shortwave radiation) minus the outgoing solar radiation at the top of the atmosphere, assuming clear-sky (cloudless) conditions. It is the amount of radiation passing through a horizontal plane. The incoming solar radiation is the amount received from the Sun. The outgoing solar radiation is the amount reflected and scattered by the Earth's atmosphere and surface, assuming clear-sky (cloudless) conditions. Clear-sky radiation quantities are computed for exactly the same atmospheric conditions of temperature, humidity, ozone, trace gases and aerosol as the total-sky (clouds included) quantities, but assuming that the clouds are not there. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

The thermal (also known as terrestrial or longwave) radiation emitted to space at the top of the atmosphere is commonly known as the Outgoing Longwave Radiation (OLR). The top net thermal radiation (this parameter) is equal to the negative of OLR. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

This parameter is the thermal (also known as terrestrial or longwave) radiation emitted to space at the top of the atmosphere, assuming clear-sky (cloudless) conditions. It is the amount passing through a horizontal plane. Note that the ECMWF convention for vertical fluxes is positive downwards, so a flux from the atmosphere to space will be negative. Clear-sky radiation quantities are computed for exactly the same atmospheric conditions of temperature, humidity, ozone, trace gases and aerosol as total-sky quantities (clouds included), but assuming that the clouds are not there. The thermal radiation emitted to space at the top of the atmosphere is commonly known as the Outgoing Longwave Radiation (OLR) (ie, taking a flux from the atmosphere to space as positive). Note that OLR is typically shown in units of watts per square metre (W m^-2 ). This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds.

This parameter is the amount of direct solar radiation (also known as shortwave radiation) reaching the surface of the Earth. It is the amount of radiation passing through a horizontal plane. Solar radiation at the surface can be direct or diffuse. Solar radiation can be scattered in all directions by particles in the atmosphere, some of which reaches the surface (diffuse solar radiation). Some solar radiation reaches the surface without being scattered (direct solar radiation). This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units are joules per square metre (J m^-2 ). To convert to watts per square metre (W m^-2 ), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.

Albedo is a measure of the reflectivity of the Earth's surface. This parameter is the fraction of diffuse solar (shortwave) radiation with wavelengths between 0.3 and 0.7 µm (microns, 1 millionth of a metre) reflected by the Earth's surface (for snow-free land surfaces only). In the ECMWF Integrated Forecasting System (IFS) albedo is dealt with separately for solar radiation with wavelengths greater/less than 0.7µm and for direct and diffuse solar radiation (giving 4 components to albedo). Solar radiation at the surface can be direct or diffuse. Solar radiation can be scattered in all directions by particles in the atmosphere, some of which reaches the surface (diffuse solar radiation). Some solar radiation reaches the surface without being scattered (direct solar radiation). In the IFS, a climatological (observed values averaged over a period of several years) background albedo is used which varies from month to month through the year, modified by the model over water, ice and snow. This parameter varies between 0 and 1.

Albedo is a measure of the reflectivity of the Earth's surface. This parameter is the fraction of direct solar (shortwave) radiation with wavelengths between 0.3 and 0.7 µm (microns, 1 millionth of a metre) reflected by the Earth's surface (for snow-free land surfaces only). In the ECMWF Integrated Forecasting System (IFS) albedo is dealt with separately for solar radiation with wavelengths greater/less than 0.7µm and for direct and diffuse solar radiation (giving 4 components to albedo). Solar radiation at the surface can be direct or diffuse. Solar radiation can be scattered in all directions by particles in the atmosphere, some of which reaches the surface (diffuse solar radiation). Some solar radiation reaches the surface without being scattered (direct solar radiation). In the IFS, a climatological (observed values averaged over a period of several years) background albedo is used which varies from month to month through the year, modified by the model over water, ice and snow.

The height above the Earth's surface of the base of the lowest cloud layer, at the specified time. This parameter is calculated by searching from the second lowest model level upwards, to the height of the level where cloud fraction becomes greater than 1% and condensate content greater than 1.E-6 kg kg^-1. Fog (ie, cloud in the lowest model layer) is not considered when defining cloud base height.

The proportion of a grid box covered by cloud occurring in the high levels of the troposphere. High cloud is a single level field calculated from cloud occurring on model levels with a pressure less than 0.45 times the surface pressure. So, if the surface pressure is 1000 hPa (hectopascal), high cloud would be calculated using levels with a pressure of less than 450 hPa (approximately 6km and above (assuming a "standard atmosphere")). The high cloud cover parameter is calculated from cloud for the appropriate model levels as described above. Assumptions are made about the degree of overlap/randomness between clouds in different model levels. Cloud fractions vary from 0 to 1.

This parameter is the proportion of a grid box covered by cloud occurring in the lower levels of the troposphere. Low cloud is a single level field calculated from cloud occurring on model levels with a pressure greater than 0.8 times the surface pressure. So, if the surface pressure is 1000 hPa (hectopascal), low cloud would be calculated using levels with a pressure greater than 800 hPa (below approximately 2km (assuming a "standard atmosphere")). Assumptions are made about the degree of overlap/randomness between clouds in different model levels. This parameter has values from 0 to 1.

This parameter is the proportion of a grid box covered by cloud occurring in the middle levels of the troposphere. Medium cloud is a single level field calculated from cloud occurring on model levels with a pressure between 0.45 and 0.8 times the surface pressure. So, if the surface pressure is 1000 hPa (hectopascal), medium cloud would be calculated using levels with a pressure of less than or equal to 800 hPa and greater than or equal to 450 hPa (between approximately 2km and 6km (assuming a "standard atmosphere")). The medium cloud parameter is calculated from cloud cover for the appropriate model levels as described above. Assumptions are made about the degree of overlap/randomness between clouds in different model levels. Cloud fractions vary from 0 to 1.

This parameter is the proportion of a grid box covered by cloud. Total cloud cover is a single level field calculated from the cloud occurring at different model levels through the atmosphere. Assumptions are made about the degree of overlap/randomness between clouds at different heights. Cloud fractions vary from 0 to 1.

This parameter is the amount of ice contained within clouds in a column extending from the surface of the Earth to the top of the atmosphere. Snow (aggregated ice crystals) is not included in this parameter. This parameter represents the area averaged value for a model grid box. Clouds contain a continuum of different sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, phase transition and aggregation are also highly simplified in the IFS.

This parameter is the amount of liquid water contained within cloud droplets in a column extending from the surface of the Earth to the top of the atmosphere. Rain water droplets, which are much larger in size (and mass), are not included in this parameter. This parameter represents the area averaged value for a model grid box. Clouds contain a continuum of different sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, phase transition and aggregation are also highly simplified in the IFS.

This parameter is the temperature of water at the bottom of inland water bodies (lakes, reservoirs, rivers and coastal waters). This parameter is defined over the whole globe, even where there is no inland water. Regions without inland water can be masked out by only considering grid points where the lake cover is greater than 0.0. In May 2015, a lake model was implemented in the ECMWF Integrated Forecasting System (IFS) to represent the water temperature and lake ice of all the world's major inland water bodies. Lake depth and area fraction (cover) are kept constant in time.

This parameter is the proportion of a grid box covered by inland water bodies (lakes, reservoirs, rivers and coastal waters). Values vary between 0: no inland water, and 1: grid box is fully covered with inland water. This parameter is specified from observations and does not vary in time. In May 2015, a lake model was implemented in the ECMWF Integrated Forecasting System (IFS) to represent the water temperature and lake ice of all the world's major inland water bodies.

This parameter is the mean depth of inland water bodies (lakes, reservoirs, rivers and coastal waters). This parameter is specified from in-situ measurements and indirect estimates and does not vary in time. This parameter is defined over the whole globe, even where there is no inland water. Regions without inland water can be masked out by only considering grid points where the lake cover is greater than 0.0. In May 2015, a lake model was implemented in the ECMWF Integrated Forecasting System (IFS) to represent the water temperature and lake ice of all the world's major inland water bodies.

This parameter is the thickness of ice on inland water bodies (lakes, reservoirs, rivers and coastal waters). This parameter is defined over the whole globe, even where there is no inland water. Regions without inland water can be masked out by only considering grid points where the lake cover is greater than 0.0. In May 2015, a lake model was implemented in the ECMWF Integrated Forecasting System (IFS) to represent the water temperature and lake ice of all the world's major inland water bodies. Lake depth and area fraction (cover) are kept constant in time. A single ice layer is used to represent the formation and melting of ice on inland water bodies. This parameter is the thickness of that ice layer.

This parameter is the temperature of the uppermost surface of ice on inland water bodies (lakes, reservoirs, rivers and coastal waters). It is the temperature at the ice/atmosphere or ice/snow interface. This parameter is defined over the whole globe, even where there is no inland water. Regions without inland water can be masked out by only considering grid points where the lake cover is greater than 0.0. In May 2015, a lake model was implemented in the ECMWF Integrated Forecasting System (IFS) to represent the water temperature and lake ice of all the world's major inland water bodies. Lake depth and area fraction (cover) are kept constant in time. A single ice layer is used to represent the formation and melting of ice on inland water bodies.

This parameter is the thickness of the uppermost layer of inland water bodies (lakes, reservoirs, rivers and coastal waters) that is well mixed and has a near constant temperature with depth (ie, a uniform distribution of temperature with depth). Mixing can occur when the density of the surface (and near-surface) water is greater than that of the water below. Mixing can also occur through the action of wind on the surface of the water. This parameter is defined over the whole globe, even where there is no inland water. Regions without inland water can be masked out by only considering grid points where the lake cover is greater than 0.0. In May 2015, a lake model was implemented in the ECMWF Integrated Forecasting System (IFS) to represent the water temperature and lake ice of all the world's major inland water bodies. Lake depth and area fraction (cover) are kept constant in time. Inland water bodies are represented with two layers in the vertical, the mixed layer above and the thermocline below, where temperature changes with depth. The upper boundary of the thermocline is located at the mixed layer bottom, and the lower boundary of the thermocline at the lake bottom. A single ice layer is used to represent the formation and melting of ice on inland water bodies.

This parameter is the temperature of the uppermost layer of inland water bodies (lakes, reservoirs, rivers and coastal waters) that is well mixed and has a near constant temperature with depth (ie, a uniform distribution of temperature with depth). Mixing can occur when the density of the surface (and near-surface) water is greater than that of the water below. Mixing can also occur through the action of wind on the surface of the water. This parameter is defined over the whole globe, even where there is no inland water. Regions without inland water can be masked out by only considering grid points where the lake cover is greater than 0.0. In May 2015, a lake model was implemented in the ECMWF Integrated Forecasting System (IFS) to represent the water temperature and lake ice of all the world's major inland water bodies. Lake depth and area fraction (cover) are kept constant in time. Inland water bodies are represented with two layers in the vertical, the mixed layer above and the thermocline below, where temperature changes with depth. The upper boundary of the thermocline is located at the mixed layer bottom, and the lower boundary of the thermocline at the lake bottom. A single ice layer is used to represent the formation and melting of ice on inland water bodies.

This parameter describes the way that temperature changes with depth in the thermocline layer of inland water bodies (lakes, reservoirs, rivers and coastal waters) ie, it describes the shape of the vertical temperature profile. It is used to calculate the lake bottom temperature and other lake-related parameters. This parameter is defined over the whole globe, even where there is no inland water. Regions without inland water can be masked out by only considering grid points where the lake cover is greater than 0.0. In May 2015, a lake model was implemented in the ECMWF Integrated Forecasting System (IFS) to represent the water temperature and lake ice of all the world's major inland water bodies. Lake depth and area fraction (cover) are kept constant in time. Inland water bodies are represented with two layers in the vertical, the mixed layer above and the thermocline below, where temperature changes with depth. The upper boundary of the thermocline is located at the mixed layer bottom, and the lower boundary of the thermocline at the lake bottom. A single ice layer is used to represent the formation and melting of ice on inland water bodies.

This parameter is the mean temperature of the total water column in inland water bodies (lakes, reservoirs, rivers and coastal waters). This parameter is defined over the whole globe, even where there is no inland water. Regions without inland water can be masked out by only considering grid points where the lake cover is greater than 0.0. In May 2015, a lake model was implemented in the ECMWF Integrated Forecasting System (IFS) to represent the water temperature and lake ice of all the world's major inland water bodies. Lake depth and area fraction (cover) are kept constant in time. Inland water bodies are represented with two layers in the vertical, the mixed layer above and the thermocline below, where temperature changes with depth. This parameter is the mean temperature over the two layers. The upper boundary of the thermocline is located at the mixed layer bottom, and the lower boundary of the thermocline at the lake bottom. A single ice layer is used to represent the formation and melting of ice on inland water bodies.

This parameter is the accumulated amount of water that has evaporated from the Earth's surface, including a simplified representation of transpiration (from vegetation), into vapour in the air above. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The ECMWF Integrated Forecasting System (IFS) convention is that downward fluxes are positive. Therefore, negative values indicate evaporation and positive values indicate condensation.

This parameter is a measure of the extent to which near-surface atmospheric conditions are conducive to the process of evaporation. It is usually considered to be the amount of evaporation, under existing atmospheric conditions, from a surface of pure water which has the temperature of the lowest layer of the atmosphere and gives an indication of the maximum possible evaporation. Potential evaporation in the current ECMWF Integrated Forecasting System (IFS) is based on surface energy balance calculations with the vegetation parameters set to "crops/mixed farming" and assuming "no stress from soil moisture". In other words, evaporation is computed for agricultural land as if it is well watered and assuming that the atmosphere is not affected by this artificial surface condition. The latter may not always be realistic. Although potential evaporation is meant to provide an estimate of irrigation requirements, the method can give unrealistic results in arid conditions due to too strong evaporation forced by dry air. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time.

Some water from rainfall, melting snow, or deep in the soil, stays stored in the soil. Otherwise, the water drains away, either over the surface (surface runoff), or under the ground (sub-surface runoff) and the sum of these two is called runoff. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units of runoff are depth in metres of water. This is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point rather than averaged over a grid box. Observations are also often taken in different units, such as mm/day, rather than the accumulated metres produced here. Runoff is a measure of the availability of water in the soil, and can, for example, be used as an indicator of drought or flood.

Some water from rainfall, melting snow, or deep in the soil, stays stored in the soil. Otherwise, the water drains away, either over the surface (surface runoff), or under the ground (sub-surface runoff) and the sum of these two is called runoff. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units of runoff are depth in metres of water. This is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point rather than averaged over a grid box. Observations are also often taken in different units, such as mm/day, rather than the accumulated metres produced here. Runoff is a measure of the availability of water in the soil, and can, for example, be used as an indicator of drought or flood.

Some water from rainfall, melting snow, or deep in the soil, stays stored in the soil. Otherwise, the water drains away, either over the surface (surface runoff), or under the ground (sub-surface runoff) and the sum of these two is called runoff. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units of runoff are depth in metres of water. This is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point rather than averaged over a grid box. Observations are also often taken in different units, such as mm/day, rather than the accumulated metres produced here. Runoff is a measure of the availability of water in the soil, and can, for example, be used as an indicator of drought or flood.

This parameter is the accumulated precipitation that falls to the Earth's surface, which is generated by the convection scheme in the ECMWF Integrated Forecasting System (IFS). The convection scheme represents convection at spatial scales smaller than the grid box. Precipitation can also be generated by the cloud scheme in the IFS, which represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. In the IFS, precipitation is comprised of rain and snow. In the IFS, precipitation is comprised of rain and snow. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is the rate of rainfall (rainfall intensity), at the Earth's surface and at the specified time, which is generated by the convection scheme in the ECMWF Integrated Forecasting System (IFS). The convection scheme represents convection at spatial scales smaller than the grid box. Rainfall can also be generated by the cloud scheme in the IFS, which represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. In the IFS, precipitation is comprised of rain and snow. This parameter is the rate the rainfall would have if it were spread evenly over the grid box. 1 kg of water spread over 1 square metre of surface is 1 mm deep (neglecting the effects of temperature on the density of water), therefore the units are equivalent to mm per second. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is the fraction of the grid box (0-1) covered by large-scale precipitation at the specified time. Large-scale precipitation is rain and snow that falls to the Earth's surface, and is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Precipitation can also be due to convection generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box.

This parameter is the accumulated precipitation that falls to the Earth's surface, which is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. Precipitation can also be generated by the convection scheme in the IFS, which represents convection at spatial scales smaller than the grid box. In the IFS, precipitation is comprised of rain and snow. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is the accumulation of the fraction of the grid box (0-1) that is covered by large-scale precipitation. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time.

This parameter is the rate of rainfall (rainfall intensity), at the Earth's surface and at the specified time, which is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. Rainfall can also be generated by the convection scheme in the IFS, which represents convection at spatial scales smaller than the grid box. In the IFS, precipitation is comprised of rain and snow. This parameter is the rate the rainfall would have if it were spread evenly over the grid box. Since 1 kg of water spread over 1 square metre of surface is 1 mm deep (neglecting the effects of temperature on the density of water), the units are equivalent to mm per second. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter describes the type of precipitation at the surface, at the specified time. A precipitation type is assigned wherever there is a non-zero value of precipitation. In the ECMWF Integrated Forecasting System (IFS) there are only two predicted precipitation variables: rain and snow. Precipitation type is derived from these two predicted variables in combination with atmospheric conditions, such as temperature. Values of precipitation type defined in the IFS: 0: No precipitation, 1: Rain, 3: Freezing rain (ie supercooled raindrops which freeze on contact with the ground and other surfaces), 5: Snow, 6: Wet snow (ie snow particles which are starting to melt); 7: Mixture of rain and snow, 8: Ice pellets. These precipitation types are consistent with WMO Code Table 4.201. Other types in this WMO table are not defined in the IFS.

This parameter is the total amount of water in droplets of raindrop size (which can fall to the surface as precipitation) in a column extending from the surface of the Earth to the top of the atmosphere. This parameter represents the area averaged value for a grid box. Clouds contain a continuum of different sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, conversion and aggregation are also highly simplified in the IFS.

This parameter is the accumulated liquid and frozen water, comprising rain and snow, that falls to the Earth's surface. It is the sum of large-scale precipitation and convective precipitation. Large-scale precipitation is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of the grid box or larger. Convective precipitation is generated by the convection scheme in the IFS, which represents convection at spatial scales smaller than the grid box. This parameter does not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is the accumulated snow that falls to the Earth's surface, which is generated by the convection scheme in the ECMWF Integrated Forecasting System (IFS). The convection scheme represents convection at spatial scales smaller than the grid box. Snowfall can also be generated by the cloud scheme in the IFS, which represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. In the IFS, precipitation is comprised of rain and snow. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is the rate of snowfall (snowfall intensity), at the Earth's surface and at the specified time, which is generated by the convection scheme in the ECMWF Integrated Forecasting System (IFS). The convection scheme represents convection at spatial scales smaller than the grid box. Snowfall can also be generated by the cloud scheme in the IFS, which represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. In the IFS, precipitation is comprised of rain and snow. This parameter is the rate the snowfall would have if it were spread evenly over the grid box. Since 1 kg of water spread over 1 square metre of surface is 1 mm thick (neglecting the effects of temperature on the density of water), the units are equivalent to mm (of liquid water) per second. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is the accumulated snow that falls to the Earth's surface, which is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. Snowfall can also be generated by the convection scheme in the IFS, which represents convection at spatial scales smaller than the grid box. In the IFS, precipitation is comprised of rain and snow. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is the rate of snowfall (snowfall intensity), at the Earth's surface and at the specified time, which is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. Snowfall can also be generated by the convection scheme in the IFS, which represents convection at spatial scales smaller than the grid box. In the IFS, precipitation is comprised of rain and snow. This parameter is the rate the snowfall would have if it were spread evenly over the grid box. Since 1 kg of water spread over 1 square metre of surface is 1 mm deep (neglecting the effects of temperature on the density of water), the units are equivalent to mm (of liquid water) per second. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is a measure of the reflectivity of the snow-covered part of the grid box. It is the fraction of solar (shortwave) radiation reflected by snow across the solar spectrum. The ECMWF Integrated Forecasting System (IFS) represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box. This parameter changes with snow age and also depends on vegetation height. It has a range of values between 0 and 1. For low vegetation, it ranges between 0.52 for old snow and 0.88 for fresh snow. For high vegetation with snow underneath, it depends on vegetation type and has values between 0.27 and 0.38. This parameter is defined over the whole globe, even where there is no snow. Regions without snow can be masked out by only considering grid points where the snow depth (m of water equivalent) is greater than 0.0.

This parameter is the mass of snow per cubic metre in the snow layer. The ECMWF Integrated Forecasting System (IFS) represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box. This parameter is defined over the whole globe, even where there is no snow. Regions without snow can be masked out by only considering grid points where the snow depth (m of water equivalent) is greater than 0.0.

This parameter is the amount of snow from the snow-covered area of a grid box. Its units are metres of water equivalent, so it is the depth the water would have if the snow melted and was spread evenly over the whole grid box. The ECMWF Integrated Forecasting System (IFS) represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box.

This parameter is the accumulated amount of water that has evaporated from snow from the snow-covered area of a grid box into vapour in the air above. The ECMWF Integrated Forecasting System (IFS) represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box. This parameter is the depth of water there would be if the evaporated snow (from the snow-covered area of a grid box) were liquid and were spread evenly over the whole grid box. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The IFS convention is that downward fluxes are positive. Therefore, negative values indicate evaporation and positive values indicate deposition.

This parameter is the accumulated snow that falls to the Earth's surface. It is the sum of large-scale snowfall and convective snowfall. Large-scale snowfall is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. Convective snowfall is generated by the convection scheme in the IFS, which represents convection at spatial scales smaller than the grid box. In the IFS, precipitation is comprised of rain and snow. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is the accumulated amount of water that has melted from snow in the snow-covered area of a grid box. The ECMWF Integrated Forecasting System (IFS) represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box. This parameter is the depth of water there would be if the melted snow (from the snow-covered area of a grid box) were spread evenly over the whole grid box. For example, if half the grid box were covered in snow with a water equivalent depth of 0.02m, this parameter would have a value of 0.01m. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time.

This parameter gives the temperature of the snow layer from the ground to the snow-air interface. The ECMWF Integrated Forecasting System (IFS) represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box. This parameter is defined over the whole globe, even where there is no snow. Regions without snow can be masked out by only considering grid points where the snow depth (m of water equivalent) is greater than 0.0.

This parameter is the total amount of water in the form of snow (aggregated ice crystals which can fall to the surface as precipitation) in a column extending from the surface of the Earth to the top of the atmosphere. This parameter represents the area averaged value for a grid box. Clouds contain a continuum of different sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, conversion and aggregation are also highly simplified in the IFS.

This parameter is the temperature of the soil at level 1 (in the middle of layer 1). The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm: Layer 1: 0 - 7cm, Layer 2: 7 - 28cm, Layer 3: 28 - 100cm, Layer 4: 100 - 289cm. Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer. Soil temperature is defined over the whole globe, even over ocean. Regions with a water surface can be masked out by only considering grid points where the land-sea mask has a value greater than 0.5.

This parameter is the temperature of the soil at level 2 (in the middle of layer 2). The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm: Layer 1: 0 - 7cm, Layer 2: 7 - 28cm, Layer 3: 28 - 100cm, Layer 4: 100 - 289cm. Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer. Soil temperature is defined over the whole globe, even over ocean. Regions with a water surface can be masked out by only considering grid points where the land-sea mask has a value greater than 0.5.

This parameter is the temperature of the soil at level 3 (in the middle of layer 3). The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm: Layer 1: 0 - 7cm, Layer 2: 7 - 28cm, Layer 3: 28 - 100cm, Layer 4: 100 - 289cm. Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer. Soil temperature is defined over the whole globe, even over ocean. Regions with a water surface can be masked out by only considering grid points where the land-sea mask has a value greater than 0.5.

This parameter is the temperature of the soil at level 4 (in the middle of layer 4). The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm: Layer 1: 0 - 7cm, Layer 2: 7 - 28cm, Layer 3: 28 - 100cm, Layer 4: 100 - 289cm. Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer. Soil temperature is defined over the whole globe, even over ocean. Regions with a water surface can be masked out by only considering grid points where the land-sea mask has a value greater than 0.5.

This parameter is the texture (or classification) of soil used by the land surface scheme of the ECMWF Integrated Forecasting System (IFS) to predict the water holding capacity of soil in soil moisture and runoff calculations. It is derived from the root zone data (30-100 cm below the surface) of the FAO/UNESCO Digital Soil Map of the World, DSMW (FAO, 2003), which exists at a resolution of 5' X 5' (about 10 km). The seven soil types are: 1: Coarse, 2: Medium, 3: Medium fine, 4: Fine, 5: Very fine, 6: Organic, 7: Tropical organic. A value of 0 indicates a non-land point. This parameter does not vary in time.

The vertical integral of the cloud frozen water flux is the horizontal rate of flow of cloud frozen water, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of cloud frozen water spreading outward from a point, per square metre. This parameter is positive for cloud frozen water that is spreading out, or diverging, and negative for the opposite, for cloud frozen water that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of cloud frozen water. Note that "cloud frozen water" is the same as "cloud ice water".

The vertical integral of the cloud liquid water flux is the horizontal rate of flow of cloud liquid water, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of cloud liquid water spreading outward from a point, per square metre. This parameter is positive for cloud liquid water that is spreading out, or diverging, and negative for the opposite, for cloud liquid water that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of cloud liquid water.

The vertical integral of the geopotential flux is the horizontal rate of flow of geopotential, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of geopotential spreading outward from a point, per square metre. This parameter is positive for geopotential that is spreading out, or diverging, and negative for the opposite, for geopotential that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of geopotential. Geopotential is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level. This parameter can be used to study the atmospheric energy budget.

The vertical integral of the kinetic energy flux is the horizontal rate of flow of kinetic energy, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of kinetic energy spreading outward from a point, per square metre. This parameter is positive for kinetic energy that is spreading out, or diverging, and negative for the opposite, for kinetic energy that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of kinetic energy. Atmospheric kinetic energy is the energy of the atmosphere due to its motion. Only horizontal motion is considered in the calculation of this parameter. This parameter can be used to study the atmospheric energy budget.

The vertical integral of the mass flux is the horizontal rate of flow of mass, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of mass spreading outward from a point, per square metre. This parameter is positive for mass that is spreading out, or diverging, and negative for the opposite, for mass that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of mass. This parameter can be used to study the atmospheric mass and energy budgets.

The vertical integral of the moisture flux is the horizontal rate of flow of moisture, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of moisture spreading outward from a point, per square metre. This parameter is positive for moisture that is spreading out, or diverging, and negative for the opposite, for moisture that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of moisture. 1 kg of water spread over 1 square metre of surface is 1 mm deep (neglecting the effects of temperature on the density of water), therefore the units are equivalent to mm (of liquid water) per second.

The vertical integral of the ozone flux is the horizontal rate of flow of ozone, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of ozone spreading outward from a point, per square metre. This parameter is positive for ozone that is spreading out, or diverging, and negative for the opposite, for ozone that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of ozone. In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including a representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air.

The vertical integral of the thermal energy flux is the horizontal rate of flow of thermal energy, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of thermal energy spreading outward from a point, per square metre. This parameter is positive for thermal energy that is spreading out, or diverging, and negative for the opposite, for thermal energy that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of thermal energy. The thermal energy is equal to enthalpy, which is the sum of the internal energy and the energy associated with the pressure of the air on its surroundings. Internal energy is the energy contained within a system ie, the microscopic energy of the air molecules, rather than the macroscopic energy associated with, for example, wind, or gravitational potential energy. The energy associated with the pressure of the air on its surroundings is the energy required to make room for the system by displacing its surroundings and is calculated from the product of pressure and volume. This parameter can be used to study the flow of thermal energy through the climate system and to investigate the atmospheric energy budget.

The vertical integral of the total energy flux is the horizontal rate of flow of total energy, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of total energy spreading outward from a point, per square metre. This parameter is positive for total energy that is spreading out, or diverging, and negative for the opposite, for total energy that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of total energy. Total atmospheric energy is made up of internal, potential, kinetic and latent energy. This parameter can be used to study the atmospheric energy budget.

This parameter is the horizontal rate of flow of cloud frozen water, in the eastward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from west to east. Note that "cloud frozen water" is the same as "cloud ice water".

This parameter is the horizontal rate of flow of cloud liquid water, in the eastward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from west to east.

This parameter is the horizontal rate of flow of geopotential, in the eastward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from west to east. Geopotential is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level. This parameter can be used to study the atmospheric energy budget.

This parameter is the horizontal rate of flow of heat in the eastward direction, per meter across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from west to east. Heat (or thermal energy) is equal to enthalpy, which is the sum of the internal energy and the energy associated with the pressure of the air on its surroundings. Internal energy is the energy contained within a system ie, the microscopic energy of the air molecules, rather than the macroscopic energy associated with, for example, wind, or gravitational potential energy. The energy associated with the pressure of the air on its surroundings is the energy required to make room for the system by displacing its surroundings and is calculated from the product of pressure and volume. This parameter can be used to study the atmospheric energy budget.

This parameter is the horizontal rate of flow of kinetic energy, in the eastward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from west to east. Atmospheric kinetic energy is the energy of the atmosphere due to its motion. Only horizontal motion is considered in the calculation of this parameter. This parameter can be used to study the atmospheric energy budget.

This parameter is the horizontal rate of flow of mass, in the eastward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from west to east. This parameter can be used to study the atmospheric mass and energy budgets.

This parameter is the horizontal rate of flow of ozone in the eastward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values denote a flux from west to east. In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including a representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air.

This parameter is the horizontal rate of flow of total energy in the eastward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from west to east. Total atmospheric energy is made up of internal, potential, kinetic and latent energy. This parameter can be used to study the atmospheric energy budget.

This parameter is the horizontal rate of flow of water vapour, in the eastward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from west to east.

This parameter is one contribution to the amount of energy being converted between kinetic energy, and internal plus potential energy, for a column of air extending from the surface of the Earth to the top of the atmosphere. Negative values indicate a conversion to kinetic energy from potential plus internal energy. This parameter can be used to study the atmospheric energy budget. The circulation of the atmosphere can also be considered in terms of energy conversions.

This parameter is the vertical integral of kinetic energy for a column of air extending from the surface of the Earth to the top of the atmosphere. Atmospheric kinetic energy is the energy of the atmosphere due to its motion. Only horizontal motion is considered in the calculation of this parameter. This parameter can be used to study the atmospheric energy budget.

This parameter is the total mass of air for a column extending from the surface of the Earth to the top of the atmosphere, per square metre. This parameter is calculated by dividing surface pressure by the Earth's gravitational acceleration, g (=9.80665 ms^-2 ), and has units of kilograms per square metre. This parameter can be used to study the atmospheric mass budget.

This parameter is the rate of change of the mass of a column of air extending from the Earth's surface to the top of the atmosphere. An increasing mass of the column indicates rising surface pressure. In contrast, a decrease indicates a falling surface pressure. The mass of the column is calculated by dividing pressure at the Earth's surface by the gravitational acceleration, g (=9.80665 ms^-2 ). This parameter can be used to study the atmospheric mass and energy budgets.

This parameter is the horizontal rate of flow of cloud frozen water, in the northward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from south to north. Note that "cloud frozen water" is the same as "cloud ice water".

This parameter is the horizontal rate of flow of cloud liquid water, in the northward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from south to north.

This parameter is the horizontal rate of flow of geopotential in the northward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from south to north. Geopotential is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level. This parameter can be used to study the atmospheric energy budget.

This parameter is the horizontal rate of flow of heat in the northward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from south to north. Heat (or thermal energy) is equal to enthalpy, which is the sum of the internal energy and the energy associated with the pressure of the air on its surroundings. Internal energy is the energy contained within a system ie, the microscopic energy of the air molecules, rather than the macroscopic energy associated with, for example, wind, or gravitational potential energy. The energy associated with the pressure of the air on its surroundings is the energy required to make room for the system by displacing its surroundings and is calculated from the product of pressure and volume. This parameter can be used to study the atmospheric energy budget.

This parameter is the horizontal rate of flow of kinetic energy, in the northward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from south to north. Atmospheric kinetic energy is the energy of the atmosphere due to its motion. Only horizontal motion is considered in the calculation of this parameter. This parameter can be used to study the atmospheric energy budget.

This parameter is the horizontal rate of flow of mass, in the northward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from south to north. This parameter can be used to study the atmospheric mass and energy budgets.

This parameter is the horizontal rate of flow of ozone in the northward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values denote a flux from south to north. In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including a representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air.

This parameter is the fraction of the grid box that is covered with vegetation that is classified as "high". The values vary between 0 and 1 but do not vary in time. This is one of the parameters in the model that describes land surface vegetation. "High vegetation" consists of evergreen trees, deciduous trees, mixed forest/woodland, and interrupted forest.

This parameter is the surface area of one side of all the leaves found over an area of land for vegetation classified as "high". This parameter has a value of 0 over bare ground or where there are no leaves. It can be calculated daily from satellite data. It is important for forecasting, for example, how much rainwater will be intercepted by the vegetative canopy, rather than falling to the ground. This is one of the parameters in the model that describes land surface vegetation. "High vegetation" consists of evergreen trees, deciduous trees, mixed forest/woodland, and interrupted forest.

This parameter is the surface area of one side of all the leaves found over an area of land for vegetation classified as "low". This parameter has a value of 0 over bare ground or where there are no leaves. It can be calculated daily from satellite data. It is important for forecasting, for example, how much rainwater will be intercepted by the vegetative canopy, rather than falling to the ground. This is one of the parameters in the model that describes land surface vegetation. "Low vegetation" consists of crops and mixed farming, irrigated crops, short grass, tall grass, tundra, semidesert, bogs and marshes, evergreen shrubs, deciduous shrubs, and water and land mixtures.

This parameter is the fraction of the grid box that is covered with vegetation that is classified as "low". The values vary between 0 and 1 but do not vary in time. This is one of the parameters in the model that describes land surface vegetation. "Low vegetation" consists of crops and mixed farming, irrigated crops, short grass, tall grass, tundra, semidesert, bogs and marshes, evergreen shrubs, deciduous shrubs, and water and land mixtures.

This parameter indicates the 6 types of high vegetation recognised by the ECMWF Integrated Forecasting System: 3 = Evergreen needleleaf trees, 4 = Deciduous needleleaf trees, 5 = Deciduous broadleaf trees, 6 = Evergreen broadleaf trees, 18 = Mixed forest/woodland, 19 = Interrupted forest. A value of 0 indicates a point without high vegetation, including an oceanic or inland water location. Vegetation types are used to calculate the surface energy balance and snow albedo. This parameter does not vary in time.

This parameter indicates the 10 types of low vegetation recognised by the ECMWF Integrated Forecasting System: 1 = Crops, Mixed farming, 2 = Grass, 7 = Tall grass, 9 = Tundra, 10 = Irrigated crops, 11 = Semidesert, 13 = Bogs and marshes, 16 = Evergreen shrubs, 17 = Deciduous shrubs, 20 = Water and land mixtures. A value of 0 indicates a point without low vegetation, including an oceanic or inland water location. Vegetation types are used to calculate the surface energy balance and snow albedo. This parameter does not vary in time.

This parameter is the mass of air per cubic metre over the oceans, derived from the temperature, specific humidity and pressure at the lowest model level in the atmospheric model. This parameter is one of the parameters used to force the wave model, therefore it is only calculated over water bodies represented in the ocean wave model. It is interpolated from the atmospheric model horizontal grid onto the horizontal grid used by the ocean wave model.

This parameter is the resistance that ocean waves exert on the atmosphere. It is sometimes also called a "friction coefficient". It is calculated by the wave model as the ratio of the square of the friction velocity, to the square of the neutral wind speed at a height of 10 metres above the surface of the Earth. The neutral wind is calculated from the surface stress and the corresponding roughness length by assuming that the air is neutrally stratified. The neutral wind is, by definition, in the direction of the surface stress. The size of the roughness length depends on the sea state.

This parameter is an estimate of the vertical velocity of updraughts generated by free convection. Free convection is fluid motion induced by buoyancy forces, which are driven by density gradients. The free convective velocity is used to estimate the impact of wind gusts on ocean wave growth. It is calculated at the height of the lowest temperature inversion (the height above the surface of the Earth where the temperature increases with height). This parameter is one of the parameters used to force the wave model, therefore it is only calculated over water bodies represented in the ocean wave model. It is interpolated from the atmospheric model horizontal grid onto the horizontal grid used by the ocean wave model.

This parameter is an estimate of the height of the expected highest individual wave within a 20 minute time window. It can be used as a guide to the likelihood of extreme or freak waves. The interactions between waves are non-linear and occasionally concentrate wave energy giving a wave height considerably larger than the significant wave height. If the maximum individual wave height is more than twice the significant wave height, then the wave is considered as a freak wave. The significant wave height represents the average height of the highest third of surface ocean/sea waves, generated by local winds and associated with swell. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is derived statistically from the two-dimensional wave spectrum. The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both.

This parameter is the mean direction of waves associated with swell. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of all swell only. It is the mean over all frequencies and directions of the total swell spectrum. The units are degrees true, which means the direction relative to the geographic location of the north pole. It is the direction that waves are coming from, so 0 degrees means "coming from the north" and 90 degrees means "coming from the east".

The mean direction of waves generated by local winds. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of wind-sea waves only. It is the mean over all frequencies and directions of the total wind-sea wave spectrum. The units are degrees true, which means the direction relative to the geographic location of the north pole. It is the direction that waves are coming from, so 0 degrees means "coming from the north" and 90 degrees means "coming from the east".

This parameter is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea associated with swell, to pass through a fixed point. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of all swell only. It is the mean over all frequencies and directions of the total swell spectrum.

This parameter is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea generated by local winds, to pass through a fixed point. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of wind-sea waves only. It is the mean over all frequencies and directions of the total wind-sea spectrum.

This parameter can be related analytically to the average slope of combined wind-sea and swell waves. It can also be expressed as a function of wind speed under some statistical assumptions. The higher the slope, the steeper the waves. This parameter indicates the roughness of the sea/ocean surface which affects the interaction between ocean and atmosphere. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is derived statistically from the two-dimensional wave spectrum.

This parameter is the mean direction of ocean/sea surface waves. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is a mean over all frequencies and directions of the two-dimensional wave spectrum. The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both. This parameter can be used to assess sea state and swell. For example, engineers use this type of wave information when designing structures in the open ocean, such as oil platforms, or in coastal applications. The units are degrees true, which means the direction relative to the geographic location of the north pole. It is the direction that waves are coming from, so 0 degrees means "coming from the north" and 90 degrees means "coming from the east".

This parameter is the mean direction of waves in the first swell partition. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. In many situations, swell can be made up of different swell systems, for example, from two distant and separate storms. To account for this, the swell spectrum is partitioned into up to three parts. The swell partitions are labelled first, second and third based on their respective wave height. Therefore, there is no guarantee of spatial coherence (the first swell partition might be from one system at one location and a different system at the neighbouring location). The units are degrees true, which means the direction relative to the geographic location of the north pole. It is the direction that waves are coming from, so 0 degrees means "coming from the north" and 90 degrees means "coming from the east".

This parameter is the mean direction of waves in the second swell partition. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. In many situations, swell can be made up of different swell systems, for example, from two distant and separate storms. To account for this, the swell spectrum is partitioned into up to three parts. The swell partitions are labelled first, second and third based on their respective wave height. Therefore, there is no guarantee of spatial coherence (the first swell partition might be from one system at one location and a different system at the neighbouring location). The units are degrees true, which means the direction relative to the geographic location of the north pole. It is the direction that waves are coming from, so 0 degrees means "coming from the north" and 90 degrees means "coming from the east".

This parameter is the mean direction of waves in the third swell partition. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. In many situations, swell can be made up of different swell systems, for example, from two distant and separate storms. To account for this, the swell spectrum is partitioned into up to three parts. The swell partitions are labelled first, second and third based on their respective wave height. Therefore, there is no guarantee of spatial coherence (the first swell partition might be from one system at one location and a different system at the neighbouring location). The units are degrees true, which means the direction relative to the geographic location of the north pole. It is the direction that waves are coming from, so 0 degrees means "coming from the north" and 90 degrees means "coming from the east".

This parameter is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is a mean over all frequencies and directions of the two-dimensional wave spectrum. The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both. This parameter can be used to assess sea state and swell. For example, engineers use such wave information when designing structures in the open ocean, such as oil platforms, or in coastal applications.

This parameter is the reciprocal of the mean frequency of the wave components that represent the sea state. All wave components have been averaged proportionally to their respective amplitude. This parameter can be used to estimate the magnitude of Stokes drift transport in deep water. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). Moments are statistical quantities derived from the two-dimensional wave spectrum.

This parameter is the reciprocal of the mean frequency of the wave components associated with swell. All wave components have been averaged proportionally to their respective amplitude. This parameter can be used to estimate the magnitude of Stokes drift transport in deep water associated with swell. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of all swell only. Moments are statistical quantities derived from the two-dimensional wave spectrum.

This parameter is the reciprocal of the mean frequency of the wave components generated by local winds. All wave components have been averaged proportionally to their respective amplitude. This parameter can be used to estimate the magnitude of Stokes drift transport in deep water associated with wind waves. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of wind-sea waves only. Moments are statistical quantities derived from the two-dimensional wave spectrum.

This parameter is equivalent to the zero-crossing mean wave period for swell. The zero-crossing mean wave period represents the mean length of time between occasions where the sea/ocean surface crosses a defined zeroth level (such as mean sea level). The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. Moments are statistical quantities derived from the two-dimensional wave spectrum.

This parameter is equivalent to the zero-crossing mean wave period for waves generated by local winds. The zero-crossing mean wave period represents the mean length of time between occasions where the sea/ocean surface crosses a defined zeroth level (such as mean sea level). The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. Moments are statistical quantities derived from the two-dimensional wave spectrum.

This parameter is the mean period of waves in the first swell partition. The wave period is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. In many situations, swell can be made up of different swell systems, for example, from two distant and separate storms. To account for this, the swell spectrum is partitioned into up to three parts. The swell partitions are labelled first, second and third based on their respective wave height. Therefore, there is no guarantee of spatial coherence (the first swell partition might be from one system at one location and a different system at the neighbouring location).

This parameter is the mean period of waves in the second swell partition. The wave period is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. In many situations, swell can be made up of different swell systems, for example, from two distant and separate storms. To account for this, the swell spectrum is partitioned into up to three parts. The swell partitions are labelled first, second and third based on their respective wave height. Therefore, there is no guarantee of spatial coherence (the second swell partition might be from one system at one location and a different system at the neighbouring location).

This parameter is the mean period of waves in the third swell partition. The wave period is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. In many situations, swell can be made up of different swell systems, for example, from two distant and separate storms. To account for this, the swell spectrum is partitioned into up to three parts. The swell partitions are labelled first, second and third based on their respective wave height. Therefore, there is no guarantee of spatial coherence (the third swell partition might be from one system at one location and a different system at the neighbouring location).

This parameter represents the mean length of time between occasions where the sea/ocean surface crosses mean sea level. In combination with wave height information, it could be used to assess the length of time that a coastal structure might be under water, for example. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). In the ECMWF Integrated Forecasting System (IFS) this parameter is calculated from the characteristics of the two-dimensional wave spectrum.

This parameter is the depth of water from the surface to the bottom of the ocean. It is used by the ocean wave model to specify the propagation properties of the different waves that could be present. Note that the ocean wave model grid is too coarse to resolve some small islands and mountains on the bottom of the ocean, but they can have an impact on surface ocean waves. The ocean wave model has been modified to reduce the wave energy flowing around or over features at spatial scales smaller than the grid box.

This parameter is the normalised vertical flux of turbulent kinetic energy from ocean waves into the ocean. The energy flux is calculated from an estimation of the loss of wave energy due to white capping waves. A white capping wave is one that appears white at its crest as it breaks, due to air being mixed into the water. When waves break in this way, there is a transfer of energy from the waves to the ocean. Such a flux is defined to be negative. The energy flux has units of Watts per metre squared, and this is normalised by being divided by the product of air density and the cube of the friction velocity.

This parameter is the normalised vertical flux of energy from wind into the ocean waves. A positive flux implies a flux into the waves. The energy flux has units of Watts per metre squared, and this is normalised by being divided by the product of air density and the cube of the friction velocity.

This parameter is the normalised surface stress, or momentum flux, from the air into the ocean due to turbulence at the air-sea interface and breaking waves. It does not include the flux used to generate waves. The ECMWF convention for vertical fluxes is positive downwards. The stress has units of Newtons per metre squared, and this is normalised by being divided by the product of air density and the square of the friction velocity.

This parameter is the direction from which the "neutral wind" blows, in degrees clockwise from true north, at a height of ten metres above the surface of the Earth. The neutral wind is calculated from the surface stress and roughness length by assuming that the air is neutrally stratified. The neutral wind is, by definition, in the direction of the surface stress. The size of the roughness length depends on the sea state. This parameter is the wind direction used to force the wave model, therefore it is only calculated over water bodies represented in the ocean wave model. It is interpolated from the atmospheric model's horizontal grid onto the horizontal grid used by the ocean wave model.

This parameter is the horizontal speed of the "neutral wind", at a height of ten metres above the surface of the Earth. The units of this parameter are metres per second. The neutral wind is calculated from the surface stress and roughness length by assuming that the air is neutrally stratified. The neutral wind is, by definition, in the direction of the surface stress. The size of the roughness length depends on the sea state. This parameter is the wind speed used to force the wave model, therefore it is only calculated over water bodies represented in the ocean wave model. It is interpolated from the atmospheric model's horizontal grid onto the horizontal grid used by the ocean wave model.

This parameter represents the period of the most energetic ocean waves generated by local winds and associated with swell. The wave period is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is calculated from the reciprocal of the frequency corresponding to the largest value (peak) of the frequency wave spectrum. The frequency wave spectrum is obtained by integrating the two-dimensional wave spectrum over all directions. The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both.

This parameter is the period of the expected highest individual wave within a 20-minute time window. It can be used as a guide to the characteristics of extreme or freak waves. Wave period is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point. Occasionally waves of different periods reinforce and interact non-linearly giving a wave height considerably larger than the significant wave height. If the maximum individual wave height is more than twice the significant wave height, then the wave is considered to be a freak wave. The significant wave height represents the average height of the highest third of surface ocean/sea waves, generated by local winds and associated with swell. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is derived statistically from the two-dimensional wave spectrum. The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both.

This parameter represents the average height of the highest third of surface ocean/sea waves generated by wind and swell. It represents the vertical distance between the wave crest and the wave trough. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both. More strictly, this parameter is four times the square root of the integral over all directions and all frequencies of the two-dimensional wave spectrum. This parameter can be used to assess sea state and swell. For example, engineers use significant wave height to calculate the load on structures in the open ocean, such as oil platforms, or in coastal applications.

This parameter represents the average height of the highest third of surface ocean/sea waves associated with swell. It represents the vertical distance between the wave crest and the wave trough. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of total swell only. More strictly, this parameter is four times the square root of the integral over all directions and all frequencies of the two-dimensional total swell spectrum. The total swell spectrum is obtained by only considering the components of the two-dimensional wave spectrum that are not under the influence of the local wind. This parameter can be used to assess swell. For example, engineers use significant wave height to calculate the load on structures in the open ocean, such as oil platforms, or in coastal applications.

This parameter represents the average height of the highest third of surface ocean/sea waves generated by the local wind. It represents the vertical distance between the wave crest and the wave trough. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of wind-sea waves only. More strictly, this parameter is four times the square root of the integral over all directions and all frequencies of the two-dimensional wind-sea wave spectrum. The wind-sea wave spectrum is obtained by only considering the components of the two-dimensional wave spectrum that are still under the influence of the local wind. This parameter can be used to assess wind-sea waves. For example, engineers use significant wave height to calculate the load on structures in the open ocean, such as oil platforms, or in coastal applications.

This parameter represents the average height of the highest third of surface ocean/sea waves associated with the first swell partition. Wave height represents the vertical distance between the wave crest and the wave trough. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. In many situations, swell can be made up of different swell systems, for example, from two distant and separate storms. To account for this, the swell spectrum is partitioned into up to three parts. The swell partitions are labelled first, second and third based on their respective wave height. Therefore, there is no guarantee of spatial coherence (the first might be from one system at one location and another system at the neighbouring location). More strictly, this parameter is four times the square root of the integral over all directions and all frequencies of the first swell partition of the two-dimensional swell spectrum. The swell spectrum is obtained by only considering the components of the two-dimensional wave spectrum that are not under the influence of the local wind. This parameter can be used to assess swell. For example, engineers use significant wave height to calculate the load on structures in the open ocean, such as oil platforms, or in coastal applications.

This parameter represents the average height of the highest third of surface ocean/sea waves associated with the second swell partition. Wave height represents the vertical distance between the wave crest and the wave trough. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. In many situations, swell can be made up of different swell systems, for example, from two distant and separate storms. To account for this, the swell spectrum is partitioned into up to three parts. The swell partitions are labelled first, second and third based on their respective wave height. Therefore, there is no guarantee of spatial coherence (the second might be from one system at one location and another system at the neighbouring location). More strictly, this parameter is four times the square root of the integral over all directions and all frequencies of the first swell partition of the two-dimensional swell spectrum. The swell spectrum is obtained by only considering the components of the two-dimensional wave spectrum that are not under the influence of the local wind. This parameter can be used to assess swell. For example, engineers use significant wave height to calculate the load on structures in the open ocean, such as oil platforms, or in coastal applications.

This parameter represents the average height of the highest third of surface ocean/sea waves associated with the third swell partition. Wave height represents the vertical distance between the wave crest and the wave trough. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. In many situations, swell can be made up of different swell systems, for example, from two distant and separate storms. To account for this, the swell spectrum is partitioned into up to three parts. The swell partitions are labelled first, second and third based on their respective wave height. Therefore, there is no guarantee of spatial coherence (the third might be from one system at one location and another system at the neighbouring location). More strictly, this parameter is four times the square root of the integral over all directions and all frequencies of the first swell partition of the two-dimensional swell spectrum. The swell spectrum is obtained by only considering the components of the two-dimensional wave spectrum that are not under the influence of the local wind. This parameter can be used to assess swell. For example, engineers use significant wave height to calculate the load on structures in the open ocean, such as oil platforms, or in coastal applications.

This parameter is one of four parameters (the others being standard deviation, slope and anisotropy) that describe the features of the orography that are too small to be resolved by the model grid. These four parameters are calculated for orographic features with horizontal scales comprised between 5 km and the model grid resolution, being derived from the height of valleys, hills and mountains at about 1 km resolution. They are used as input for the sub-grid orography scheme which represents low-level blocking and orographic gravity wave effects. The angle of the sub-grid scale orography characterises the geographical orientation of the terrain in the horizontal plane (from a bird's-eye view) relative to an eastwards axis. This parameter does not vary in time.

This parameter is one of four parameters (the others being standard deviation, slope and angle of sub-gridscale orography) that describe the features of the orography that are too small to be resolved by the model grid. These four parameters are calculated for orographic features with horizontal scales comprised between 5 km and the model grid resolution, being derived from the height of valleys, hills and mountains at about 1 km resolution. They are used as input for the sub-grid orography scheme which represents low-level blocking and orographic gravity wave effects. This parameter is a measure of how much the shape of the terrain in the horizontal plane (from a bird's-eye view) is distorted from a circle. A value of one is a circle, less than one an ellipse, and 0 is a ridge. In the case of a ridge, wind blowing parallel to it does not exert any drag on the flow, but wind blowing perpendicular to it exerts the maximum drag. This parameter does not vary in time.

This parameter is used to calculate the likelihood of freak ocean waves, which are waves that are higher than twice the mean height of the highest third of waves. Large values of this parameter (in practice of the order 1) indicate increased probability of the occurrence of freak waves. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is derived from the statistics of the two-dimensional wave spectrum. More precisely, it is the square of the ratio of the integral ocean wave steepness and the relative width of the frequency spectrum of the waves. Further information on the calculation of this parameter is given in Section 10.6 of the ECMWF Wave Model documentation.

This parameter is the accumulated conversion of kinetic energy in the mean flow into heat, over the whole atmospheric column, per unit area, that is due to the effects of stress associated with turbulent eddies near the surface and turbulent orographic form drag. It is calculated by the ECMWF Integrated Forecasting System's turbulent diffusion and turbulent orographic form drag schemes. The turbulent eddies near the surface are related to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km, which are specified from land surface data at about 1 km resolution. (The dissipation associated with orographic features with horizontal scales between 5 km and the model grid-scale is accounted for by the sub-grid orographic scheme.) This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time.

This parameter is the depth of air next to the Earth's surface which is most affected by the resistance to the transfer of momentum, heat or moisture across the surface. The boundary layer height can be as low as a few tens of metres, such as in cooling air at night, or as high as several kilometres over the desert in the middle of a hot sunny day. When the boundary layer height is low, higher concentrations of pollutants (emitted from the Earth's surface) can develop. The boundary layer height calculation is based on the bulk Richardson number (a measure of the atmospheric conditions) following the conclusions of a 2012 review.

This parameter accounts for increased aerodynamic roughness as wave heights grow due to increasing surface stress. It depends on the wind speed, wave age and other aspects of the sea state and is used to calculate how much the waves slow down the wind. When the atmospheric model is run without the ocean model, this parameter has a constant value of 0.018. When the atmospheric model is coupled to the ocean model, this parameter is calculated by the ECMWF Wave Model.

This is an indication of the instability (or stability) of the atmosphere and can be used to assess the potential for the development of convection, which can lead to heavy rainfall, thunderstorms and other severe weather. In the ECMWF Integrated Forecasting System (IFS), CAPE is calculated by considering parcels of air departing at different model levels below the 350 hPa level. If a parcel of air is more buoyant (warmer and/or with more moisture) than its surrounding environment, it will continue to rise (cooling as it rises) until it reaches a point where it no longer has positive buoyancy. CAPE is the potential energy represented by the total excess buoyancy. The maximum CAPE produced by the different parcels is the value retained. Large positive values of CAPE indicate that an air parcel would be much warmer than its surrounding environment and therefore, very buoyant. CAPE is related to the maximum potential vertical velocity of air within an updraft; thus, higher values indicate greater potential for severe weather. Observed values in thunderstorm environments often may exceed 1000 joules per kilogram (J kg^-1), and in extreme cases may exceed 5000 J kg^-1. The calculation of this parameter assumes: (i) the parcel of air does not mix with surrounding air; (ii) ascent is pseudo-adiabatic (all condensed water falls out) and (iii) other simplifications related to the mixed-phase condensational heating.

This parameter is a measure of the amount of energy required for convection to commence. If the value of this parameter is too high, then deep, moist convection is unlikely to occur even if the convective available potential energy or convective available potential energy shear are large. CIN values greater than 200 J kg^-1 would be considered high. An atmospheric layer where temperature increases with height (known as a temperature inversion) would inhibit convective uplift and is a situation in which convective inhibition would be large.

Duct base height as diagnosed from the vertical gradient of atmospheric refractivity.

Air flowing over a surface exerts a stress (drag) that transfers momentum to the surface and slows the wind. This parameter is the component of the accumulated surface stress in an eastward direction, associated with low-level, orographic blocking and orographic gravity waves. It is calculated by the ECMWF Integrated Forecasting System's sub-grid orography scheme, which represents stress due to unresolved valleys, hills and mountains with horizontal scales between 5 km and the model grid-scale. (The stress associated with orographic features with horizontal scales smaller than 5 km is accounted for by the turbulent orographic form drag scheme). Orographic gravity waves are oscillations in the flow maintained by the buoyancy of displaced air parcels, produced when air is deflected upwards by hills and mountains. This process can create stress on the atmosphere at the Earth's surface and at other levels in the atmosphere. Positive (negative) values indicate stress on the surface of the Earth in an eastward (westward) direction. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time.

Air flowing over a surface exerts a stress (drag) that transfers momentum to the surface and slows the wind. This parameter is the component of the accumulated surface stress in an eastward direction, associated with turbulent eddies near the surface and turbulent orographic form drag. It is calculated by the ECMWF Integrated Forecasting System's turbulent diffusion and turbulent orographic form drag schemes. The turbulent eddies near the surface are related to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km, which are specified from land surface data at about 1 km resolution. (The stress associated with orographic features with horizontal scales between 5 km and the model grid-scale is accounted for by the sub-grid orographic scheme.) Positive (negative) values indicate stress on the surface of the Earth in an eastward (westward) direction. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time.

This parameter is a measure of the reflectivity of the Earth's surface. It is the fraction of short-wave (solar) radiation reflected by the Earth's surface, for diffuse radiation, assuming a fixed spectrum of downward short-wave radiation at the surface. The values of this parameter vary between zero and one. Typically, snow and ice have high reflectivity with albedo values of 0.8 and above, land has intermediate values between about 0.1 and 0.4 and the ocean has low values of 0.1 or less. Short-wave radiation from the Sun is partly reflected back to space by clouds and particles in the atmosphere (aerosols) and some of it is absorbed. The remainder is incident on the Earth's surface, where some of it is reflected. The portion that is reflected by the Earth's surface depends on the albedo. In the ECMWF Integrated Forecasting System (IFS), a climatological background albedo (observed values averaged over a period of several years) is used, modified by the model over water, ice and snow. Albedo is often shown as a percentage (%).

This parameter is the aerodynamic roughness length in metres. It is a measure of the surface resistance. This parameter is used to determine the air to surface transfer of momentum. For given atmospheric conditions, a higher surface roughness causes a slower near-surface wind speed. Over ocean, surface roughness depends on the waves. Over land, surface roughness is derived from the vegetation type and snow cover.

Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. This parameter is a theoretical wind speed at the Earth's surface that expresses the magnitude of stress. It is calculated by dividing the surface stress by air density and taking its square root. For turbulent flow, the friction velocity is approximately constant in the lowest few metres of the atmosphere. This parameter increases with the roughness of the surface. It is used to calculate the way wind changes with height in the lowest levels of the atmosphere.

This parameter is the accumulated conversion of kinetic energy in the mean flow into heat, over the whole atmospheric column, per unit area, that is due to the effects of stress associated with low-level, orographic blocking and orographic gravity waves. It is calculated by the ECMWF Integrated Forecasting System's sub-grid orography scheme, which represents stress due to unresolved valleys, hills and mountains with horizontal scales between 5 km and the model grid-scale. (The dissipation associated with orographic features with horizontal scales smaller than 5 km is accounted for by the turbulent orographic form drag scheme). Orographic gravity waves are oscillations in the flow maintained by the buoyancy of displaced air parcels, produced when air is deflected upwards by hills and mountains. This process can create stress on the atmosphere at the Earth's surface and at other levels in the atmosphere. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time.

Air flowing over a surface exerts a stress (drag) that transfers momentum to the surface and slows the wind. This parameter is the component of the surface stress at the specified time, in an eastward direction, associated with turbulent eddies near the surface and turbulent orographic form drag. It is calculated by the ECMWF Integrated Forecasting System's turbulent diffusion and turbulent orographic form drag schemes. The turbulent eddies near the surface are related to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km, which are specified from land surface data at about 1 km resolution. (The stress associated with orographic features with horizontal scales between 5 km and the model grid-scale is accounted for by the sub-grid orographic scheme.) Positive (negative) values indicate stress on the surface of the Earth in an eastward (westward) direction.

This parameter is the net rate of moisture exchange between the land/ocean surface and the atmosphere, due to the processes of evaporation (including evapotranspiration) and condensation, at the specified time. By convention, downward fluxes are positive, which means that evaporation is represented by negative values and condensation by positive values.

Air flowing over a surface exerts a stress (drag) that transfers momentum to the surface and slows the wind. This parameter is the component of the surface stress at the specified time, in a northward direction, associated with turbulent eddies near the surface and turbulent orographic form drag. It is calculated by the ECMWF Integrated Forecasting System's turbulent diffusion and turbulent orographic form drag schemes. The turbulent eddies near the surface are related to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km, which are specified from land surface data at about 1 km resolution. (The stress associated with orographic features with horizontal scales between 5 km and the model grid-scale is accounted for by the sub-grid orographic scheme.) Positive (negative) values indicate stress on the surface of the Earth in a northward (southward) direction.

This parameter is a measure of the potential for a thunderstorm to develop, calculated from the temperature and dew point temperature in the lower part of the atmosphere. The calculation uses the temperature at 850, 700 and 500 hPa and dewpoint temperature at 850 and 700 hPa. Higher values of K indicate a higher potential for the development of thunderstorms. This parameter is related to the probability of occurrence of a thunderstorm: <20 K No thunderstorm, 20-25 K Isolated thunderstorms, 26-30 K Widely scattered thunderstorms, 31-35 K Scattered thunderstorms, >35 K Numerous thunderstorms.

This parameter is the proportion of land, as opposed to ocean or inland waters (lakes, reservoirs, rivers and coastal waters), in a grid box. This parameter has values ranging between zero and one and is dimensionless. In cycles of the ECMWF Integrated Forecasting System (IFS) from CY41R1 (introduced in May 2015) onwards, grid boxes where this parameter has a value above 0.5 can be comprised of a mixture of land and inland water but not ocean. Grid boxes with a value of 0.5 and below can only be comprised of a water surface. In the latter case, the lake cover is used to determine how much of the water surface is ocean or inland water. In cycles of the IFS before CY41R1, grid boxes where this parameter has a value above 0.5 can only be comprised of land and those grid boxes with a value of 0.5 and below can only be comprised of ocean. In these older model cycles, there is no differentiation between ocean and inland water. This parameter does not vary in time.

Mean vertical gradient of atmospheric refractivity inside the trapping layer.

Minimum vertical gradient of atmospheric refractivity inside the trapping layer.

Air flowing over a surface exerts a stress (drag) that transfers momentum to the surface and slows the wind. This parameter is the component of the accumulated surface stress in a northward direction, associated with low-level, orographic blocking and orographic gravity waves. It is calculated by the ECMWF Integrated Forecasting System's sub-grid orography scheme, which represents stress due to unresolved valleys, hills and mountains with horizontal scales between 5 km and the model grid-scale. (The stress associated with orographic features with horizontal scales smaller than 5 km is accounted for by the turbulent orographic form drag scheme). Orographic gravity waves are oscillations in the flow maintained by the buoyancy of displaced air parcels, produced when air is deflected upwards by hills and mountains. This process can create stress on the atmosphere at the Earth's surface and at other levels in the atmosphere. Positive (negative) values indicate stress on the surface of the Earth in a northward (southward) direction. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time.

Air flowing over a surface exerts a stress (drag) that transfers momentum to the surface and slows the wind. This parameter is the component of the accumulated surface stress in a northward direction, associated with turbulent eddies near the surface and turbulent orographic form drag. It is calculated by the ECMWF Integrated Forecasting System's turbulent diffusion and turbulent orographic form drag schemes. The turbulent eddies near the surface are related to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km, which are specified from land surface data at about 1 km resolution. (The stress associated with orographic features with horizontal scales between 5 km and the model grid-scale is accounted for by the sub-grid orographic scheme.) Positive (negative) values indicate stress on the surface of the Earth in a northward (southward) direction. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time.

This parameter is the fraction of a grid box which is covered by sea ice. Sea ice can only occur in a grid box which includes ocean or inland water according to the land-sea mask and lake cover, at the resolution being used. This parameter can be known as sea-ice (area) fraction, sea-ice concentration and more generally as sea-ice cover. In ERA5, sea-ice cover is given by two external providers. Before 1979 the HadISST2 dataset is used. From 1979 to August 2007 the OSI SAF (409a) dataset is used and from September 2007 the OSI SAF oper dataset is used. Sea ice is frozen sea water which floats on the surface of the ocean. Sea ice does not include ice which forms on land such as glaciers, icebergs and ice-sheets. It also excludes ice shelves which are anchored on land, but protrude out over the surface of the ocean. These phenomena are not modelled by the IFS. Long-term monitoring of sea ice is important for understanding climate change. Sea ice also affects shipping routes through the polar regions.

This parameter is the amount of water in the vegetation canopy and/or in a thin layer on the soil. It represents the amount of rain intercepted by foliage, and water from dew. The maximum amount of "skin reservoir content" a grid box can hold depends on the type of vegetation, and may be zero. Water leaves the "skin reservoir" by evaporation.

This parameter is one of four parameters (the others being standard deviation, angle and anisotropy) that describe the features of the orography that are too small to be resolved by the model grid. These four parameters are calculated for orographic features with horizontal scales comprised between 5 km and the model grid resolution, being derived from the height of valleys, hills and mountains at about 1 km resolution. They are used as input for the sub-grid orography scheme which represents low-level blocking and orographic gravity wave effects. This parameter represents the slope of the sub-grid valleys, hills and mountains. A flat surface has a value of 0, and a 45 degree slope has a value of 0.5. This parameter does not vary in time.

Climatological parameter (scales between approximately 3 and 22 km are included). This parameter does not vary in time.

This parameter is one of four parameters (the others being angle of sub-gridscale orography, slope and anisotropy) that describe the features of the orography that are too small to be resolved by the model grid. These four parameters are calculated for orographic features with horizontal scales comprised between 5 km and the model grid resolution, being derived from the height of valleys, hills and mountains at about 1 km resolution. They are used as input for the sub-grid orography scheme which represents low-level blocking and orographic gravity wave effects. This parameter represents the standard deviation of the height of the sub-grid valleys, hills and mountains within a grid box. This parameter does not vary in time.

This parameter is the total amount of ozone in a column of air extending from the surface of the Earth to the top of the atmosphere. This parameter can also be referred to as total ozone, or vertically integrated ozone. The values are dominated by ozone within the stratosphere. In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms. In the IFS, the units for total ozone are kilograms per square metre, but before 12/06/2001 dobson units were used. Dobson units (DU) are still used extensively for total column ozone. 1 DU = 2.1415E-5 kg m^-2

This parameter is the total amount of supercooled water in a column extending from the surface of the Earth to the top of the atmosphere. Supercooled water is water that exists in liquid form below 0oC. It is common in cold clouds and is important in the formation of precipitation. Also, supercooled water in clouds extending to the surface (ie, fog) can cause icing/riming of various structures. This parameter represents the area averaged value for a grid box. Clouds contain a continuum of different sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, conversion and aggregation are also highly simplified in the IFS.

This parameter is the sum of water vapour, liquid water, cloud ice, rain and snow in a column extending from the surface of the Earth to the top of the atmosphere. In old versions of the ECMWF model (IFS), rain and snow were not accounted for.

This parameter is the total amount of water vapour in a column extending from the surface of the Earth to the top of the atmosphere. This parameter represents the area averaged value for a grid box.

This parameter gives an indication of the probability of occurrence of a thunderstorm and its severity by using the vertical gradient of temperature and humidity. The values of this index indicate the following: <44 Thunderstorms not likely, 44-50 Thunderstorms likely, 51-52 Isolated severe thunderstorms, 53-56 Widely scattered severe thunderstorms, 56-60 Scattered severe thunderstorms more likely. The total totals index is the temperature difference between 850 hPa (near surface) and 500 hPa (mid-troposphere) (lapse rate) plus a measure of the moisture content between 850 hPa and 500 hPa. The probability of deep convection tends to increase with increasing lapse rate and atmospheric moisture content. There are a number of limitations to this index. Also, the interpretation of the index value varies with season and location.

Trapping layer base height as diagnosed from the vertical gradient of atmospheric refractivity.

Trapping layer top height as diagnosed from the vertical gradient of atmospheric refractivity.

This parameter is the eastward component of the surface Stokes drift. The Stokes drift is the net drift velocity due to surface wind waves. It is confined to the upper few metres of the ocean water column, with the largest value at the surface. For example, a fluid particle near the surface will slowly move in the direction of wave propagation.

This parameter is the northward component of the surface Stokes drift. The Stokes drift is the net drift velocity due to surface wind waves. It is confined to the upper few metres of the ocean water column, with the largest value at the surface. For example, a fluid particle near the surface will slowly move in the direction of wave propagation.

This parameter is the horizontal rate of flow of total energy in the northward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from south to north. Total atmospheric energy is made up of internal, potential, kinetic and latent energy. This parameter can be used to study the atmospheric energy budget.

This parameter is the horizontal rate of flow of water vapour, in the northward direction, per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Positive values indicate a flux from south to north.

This parameter is the mass weighted vertical integral of potential and internal energy for a column of air extending from the surface of the Earth to the top of the atmosphere. The potential energy of an air parcel is the amount of work that would have to be done, against the force of gravity, to lift the air to that location from mean sea level. Internal energy is the energy contained within a system ie, the microscopic energy of the air molecules, rather than the macroscopic energy associated with, for example, wind, or gravitational potential energy. This parameter can be used to study the atmospheric energy budget. Total atmospheric energy is made up of internal, potential, kinetic and latent energy.

This parameter is the mass weighted vertical integral of potential, internal and latent energy for a column of air extending from the surface of the Earth to the top of the atmosphere. The potential energy of an air parcel is the amount of work that would have to be done, against the force of gravity, to lift the air to that location from mean sea level. Internal energy is the energy contained within a system ie, the microscopic energy of the air molecules, rather than the macroscopic energy associated with, for example, wind, or gravitational potential energy. The latent energy refers to the energy associated with the water vapour in the atmosphere and is equal to the energy required to convert liquid water into water vapour. This parameter can be used to study the atmospheric energy budget. Total atmospheric energy is made up of internal, potential, kinetic and latent energy.

This parameter is the mass-weighted vertical integral of temperature for a column of air extending from the surface of the Earth to the top of the atmosphere. This parameter can be used to study the atmospheric energy budget.

This parameter is the mass-weighted vertical integral of thermal energy for a column of air extending from the surface of the Earth to the top of the atmosphere. Thermal energy is calculated from the product of temperature and the specific heat capacity of air at constant pressure. The thermal energy is equal to enthalpy, which is the sum of the internal energy and the energy associated with the pressure of the air on its surroundings. Internal energy is the energy contained within a system ie, the microscopic energy of the air molecules, rather than the macroscopic energy associated with, for example, wind, or gravitational potential energy. The energy associated with the pressure of the air on its surroundings is the energy required to make room for the system by displacing its surroundings and is calculated from the product of pressure and volume. This parameter can be used to study the atmospheric energy budget. Total atmospheric energy is made up of internal, potential, kinetic and latent energy.

This parameter is the vertical integral of total energy for a column of air extending from the surface of the Earth to the top of the atmosphere. Total atmospheric energy is made up of internal, potential, kinetic and latent energy. This parameter can be used to study the atmospheric energy budget.

The vertical integral of the moisture flux is the horizontal rate of flow of moisture (water vapour, cloud liquid and cloud ice), per metre across the flow, for a column of air extending from the surface of the Earth to the top of the atmosphere. Its horizontal divergence is the rate of moisture spreading outward from a point, per square metre. This parameter is accumulated over a particular time period which depends on the data extracted. For the reanalysis, the accumulation period is over the 1 hour ending at the validity date and time. For the ensemble members, ensemble mean and ensemble spread, the accumulation period is over the 3 hours ending at the validity date and time. This parameter is positive for moisture that is spreading out, or diverging, and negative for the opposite, for moisture that is concentrating, or converging (convergence). This parameter thus indicates whether atmospheric motions act to decrease (for divergence) or increase (for convergence) the vertical integral of moisture, over the time period. High negative values of this parameter (ie large moisture convergence) can be related to precipitation intensification and floods. 1 kg of water spread over 1 square metre of surface is 1 mm deep (neglecting the effects of temperature on the density of water), therefore the units are equivalent to mm.

This parameter is the volume of water in soil layer 1 (0 - 7cm, the surface is at 0cm). The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil: Layer 1: 0 - 7cm, Layer 2: 7 - 28cm, Layer 3: 28 - 100cm, Layer 4: 100 - 289cm. Soil water is defined over the whole globe, even over ocean. Regions with a water surface can be masked out by only considering grid points where the land-sea mask has a value greater than 0.5. The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.

This parameter is the volume of water in soil layer 2 (7 - 28cm, the surface is at 0cm). The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil: Layer 1: 0 - 7cm, Layer 2: 7 - 28cm, Layer 3: 28 - 100cm, Layer 4: 100 - 289cm. Soil water is defined over the whole globe, even over ocean. Regions with a water surface can be masked out by only considering grid points where the land-sea mask has a value greater than 0.5. The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.

This parameter is the volume of water in soil layer 3 (28 - 100cm, the surface is at 0cm). The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil: Layer 1: 0 - 7cm, Layer 2: 7 - 28cm, Layer 3: 28 - 100cm, Layer 4: 100 - 289cm. Soil water is defined over the whole globe, even over ocean. Regions with a water surface can be masked out by only considering grid points where the land-sea mask has a value greater than 0.5. The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.

This parameter is the volume of water in soil layer 4 (100 - 289cm, the surface is at 0cm). The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil: Layer 1: 0 - 7cm, Layer 2: 7 - 28cm, Layer 3: 28 - 100cm, Layer 4: 100 - 289cm. Soil water is defined over the whole globe, even over ocean. Regions with a water surface can be masked out by only considering grid points where the land-sea mask has a value greater than 0.5. The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.

This parameter indicates whether waves (generated by local winds and associated with swell) are coming from similar directions or from a wide range of directions. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). Many ECMWF wave parameters (such as the mean wave period) give information averaged over all wave frequencies and directions, so do not give any information about the distribution of wave energy across frequencies and directions. This parameter gives more information about the nature of the two-dimensional wave spectrum. This parameter is a measure of the range of wave directions for each frequency integrated across the two-dimensional spectrum. This parameter takes values between 0 and the square root of 2. Where 0 corresponds to a uni-directional spectrum (ie, all wave frequencies from the same direction) and the square root of 2 indicates a uniform spectrum (ie, all wave frequencies from a different direction).

This parameter indicates whether waves associated with swell are coming from similar directions or from a wide range of directions. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of all swell only. Many ECMWF wave parameters (such as the mean wave period) give information averaged over all wave frequencies and directions, so do not give any information about the distribution of wave energy across frequencies and directions. This parameter gives more information about the nature of the two-dimensional wave spectrum. This parameter is a measure of the range of wave directions for each frequency integrated across the two-dimensional spectrum. This parameter takes values between 0 and the square root of 2. Where 0 corresponds to a uni-directional spectrum (ie, all wave frequencies from the same direction) and the square root of 2 indicates a uniform spectrum (ie, all wave frequencies from a different direction).

This parameter indicates whether waves generated by the local wind are coming from similar directions or from a wide range of directions. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of wind-sea waves only. Many ECMWF wave parameters (such as the mean wave period) give information averaged over all wave frequencies and directions, so do not give any information about the distribution of wave energy across frequencies and directions. This parameter gives more information about the nature of the two-dimensional wave spectrum. This parameter is a measure of the range of wave directions for each frequency integrated across the two-dimensional spectrum. This parameter takes values between 0 and the square root of 2. Where 0 corresponds to a uni-directional spectrum (ie, all wave frequencies from the same direction) and the square root of 2 indicates a uniform spectrum (ie, all wave frequencies from a different direction).

This parameter is a statistical measure used to forecast extreme or freak ocean/sea waves. It describes the nature of the sea surface elevation and how it is affected by waves generated by local winds and associated with swell. Under typical conditions, the sea surface elevation, as described by its probability density function, has a near normal distribution in the statistical sense. However, under certain wave conditions the probability density function of the sea surface elevation can deviate considerably from normality, signalling increased probability of freak waves. This parameter gives one measure of the deviation from normality. It shows how much of the probability density function of the sea surface elevation exists in the tails of the distribution. So, a positive kurtosis (typical range 0.0 to 0.06) means more frequent occurrences of very extreme values (either above or below the mean), relative to a normal distribution.

This parameter is a statistical measure used to forecast extreme or freak waves. It is a measure of the relative width of the ocean/sea wave frequency spectrum (ie, whether the ocean/sea wave field is made up of a narrow or broad range of frequencies). The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). When the wave field is more focussed around a narrow range of frequencies, the probability of freak/extreme waves increases. This parameter is Goda's peakedness factor and is used to calculate the Benjamin-Feir Index (BFI). The BFI is in turn used to estimate the probability and nature of extreme/freak waves.

This parameter is a statistical measure used to forecast extreme or freak ocean/sea waves. It describes the nature of the sea surface elevation and how it is affected by waves generated by local winds and associated with swell. Under typical conditions, the sea surface elevation, as described by its probability density function, has a near normal distribution in the statistical sense. However, under certain wave conditions the probability density function of the sea surface elevation can deviate considerably from normality, signalling increased probability of freak waves. This parameter gives one measure of the deviation from normality. It is a measure of the asymmetry of the probability density function of the sea surface elevation. So, a positive/negative skewness (typical range -0.2 to 0.12) means more frequent occurrences of extreme values above/below the mean, relative to a normal distribution.

The height above the Earth's surface where the temperature passes from positive to negative values, corresponding to the top of a warm layer, at the specified time. This parameter can be used to help forecast snow. If more than one warm layer is encountered, then the zero degree level corresponds to the top of the second atmospheric layer. This parameter is set to zero when the temperature in the whole atmosphere is below 0°C.

Maximum 3 second wind at 10 m height as defined by WMO. Parametrization represents turbulence only before 01102008; thereafter effects of convection are included. The 3 s gust is computed every time step and and the maximum is kept since the last postprocessing.

This parameter is the gravitational potential energy of a unit mass, at a particular location at the surface of the Earth, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level. The (surface) geopotential height (orography) can be calculated by dividing the (surface) geopotential by the Earth's gravitational acceleration, g (=9.80665 ms^-2 ). This parameter does not vary in time.

This parameter is the highest temperature of air at 2m above the surface of land, sea or inland water since the parameter was last archived in a particular forecast. 2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions.

The total precipitation is calculated from the combined large-scale and convective rainfall and snowfall rates every time step and the maximum is kept since the last postprocessing.

This parameter is the lowest temperature of air at 2m above the surface of land, sea or inland waters since the parameter was last archived in a particular forecast. 2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.

The total precipitation is calculated from the combined large-scale and convective rainfall and snowfall rates every time step and the minimum is kept since the last postprocessing.

The divergence of the wind at the 500hPa pressure level.

The divergence of the wind at the 850hPa pressure level.

The fraction of cloud cover at the 500hPa pressure level.

The fraction of cloud cover at the 850hPa pressure level.

The mass mixing ratio of ozone at the 500hPa pressure level.

The mass mixing ratio of ozone at the 850hPa pressure level.

The potential vorticity at the 500hPa pressure level.

The potential vorticity at the 850hPa pressure level.

The relative humidity at the 500hPa pressure level.

The relative humidity at the 850hPa pressure level.

The specific cloud ice water content at the 500hPa pressure level.

The specific cloud ice water content at the 850hPa pressure level.

The specific cloud liquid water content at the 500hPa pressure level.

The specific cloud liquid water content at the 850hPa pressure level.

The specific humidity at the 500hPa pressure level.

The specific humidity at the 850hPa pressure level.

The specific rain water content at the 500hPa pressure level.

The specific rain water content at the 850hPa pressure level.

The specific snow water content at the 500hPa pressure level.

The specific snow water content at the 850hPa pressure level.

The temperature at the 500hPa pressure level.

The temperature at the 850hPa pressure level.

The eastward component of the wind at the 500hPa pressure level.

The eastward component of the wind at the 850hPa pressure level.

The northward component of the wind at the 500hPa pressure level.

The northward component of the wind at the 850hPa pressure level.

The vertical velocity at the 500hPa pressure level.

The vertical velocity at the 850hPa pressure level.

The vorticity of the wind at the 500hPa pressure level.

The vorticity of the wind at the 850hPa pressure level.

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