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The available CERRA-Land variables in the CDS are eitherinstantaneous, accumulated or static. The natural, urban and inland water fraction will be available in netCDF format only. This is specified for each of the variables listed in the tables below.

Overview of variables calculated as a mean value of a grib box

Table 1: Overview of variables calculated as a mean value of a grib box.

Albedo

The albedo [0-100%] is the total reflectance of downward solar radiation at the surface over the grid box. The albedo is the ratio of one hour time-integrated surface solar radiation upward by the one hour time-integrated surface solar radiation downward. Multiplying the albedo with the one hour accumulated downward solar radiation gives the one hour accumulated upward solar radiation.

Evaporation

Evaporation is the amount of water that has evaporated from the earth’s surface from the initial time of the forecast to the forecast time step. It is given as a mean for the grid area between the three surface types in the grid - inland water, natural land and urban. Hence, evaporation is represented by negative values and positive values represent condensation. By model convention downward fluxes are positive. It is an accumulated variable.

Total precipitation

The total precipitation is the amount of precipitation falling at the surface during the last 24-hours. It includes all kind of precipitation forms as convective precipitation, large scale precipitation, liquid and solid precipitation. The total precipitation is available only for the analyses at 06 UTC. It is an accumulated field from the previous day at 06 UTC to the present day at 06 UTC. The date in the metadata GRIB2 file represents the end of the accumulation period.

Skin temperature 

It represents the average air temperature at the surface of each grid box. The skin temperature is an average of temperatures given by the three surface types in the grid - inland water, natural land and urban. It is an instantaneous variable.

Surface latent heat flux

The surface latent heat flux is the accumulated exchange of latent heat (due to phase transitions - evaporation, condensation) with the surface (ground and water) through turbulent diffusion from the initial time of the forecast to the forecast time step. It is given as a mean for the grid area between the three surface types in the grid - inland water, natural land and urban. By model convention downward fluxes are positive. It is an accumulated variable.

Surface sensible heat flux

The surface sensible heat flux is the accumulated exchange of heat (no phase transition) with the surface (ground and water) through turbulent diffusion from the initial time of the forecast to the forecast time step. It is given as a mean for the grid area between the three surface types in the grid - inland water, natural land and urban. By model convention downward fluxes are positive. It is an accumulated variable.

Surface net solar radiation

The surface net solar radiation is the accumulated solar short-wave radiation that is absorbed at the surface from the initial time of the forecast to the forecast time step. It is calculated as the difference between the downward solar energy and the upward solar energy at the surface. By model convention downward fluxes are positive. It is an accumulated variable.

Surface solar radiation downwards

The surface solar radiation downward is the accumulated total (direct and diffuse) solar short-wave radiation reaching the surface from the initial time of the forecast to the forecast time step. By model convention downward fluxes are positive. It is an accumulated variable.

Surface net thermal radiation

The net thermal radiation at the surface is accumulated from the initial time of the forecast to the forecast time step. It is calculated as the difference between the thermal radiation downwards and the upward thermal radiation at the surface. By model convention downward fluxes are positive. It is an accumulated variable.

Surface thermal radiation downwards

The surface thermal radiation downward is the amount of thermal (long-wave) radiation reaching the surface accumulated from the initial time of the forecast to the forecast time step. By model convention downward fluxes are positive. It is an accumulated variable.

Soil heat flux 

The soil heat flux is the energy receive by the soil to heat it per unit of surface and time. The Soil heat flux is positive when the soil receives energy (warms) and negative when the soil loses energy (cools). It is an instantaneous variable.

Surface roughness 

The surface roughness describes the aerodynamic roughness length. It is given as a mean for the grid area between the three surface types in the grid (inland water, natural land and urban) and has missing values over the ocean. The roughness length of the surface is the height above the surface at which the wind profile is assumed to become zero. Each grid point has one value representing the mean over the grid point. The effective surface roughness is depending on the orographic component (constant part), the snow depth, the evolution of the Leaf Area Index and the fraction of vegetation, which is different for each month. It is an instantaneous variable.

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Overview of variables available for the natural land fraction

snow variables

The snow variables are related to natural land only. The fraction of snow cover represents the fraction of natural land which has snow on the ground. Snow on urban or lake fraction is not available.

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Table 2: Overview of variables available for the natural land fraction.

 Fraction of snow cover

It represents the fraction (0-1) occupied by snow for nature fraction only. It is an instantaneous variable.

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Melting of snow. This variable is accumulated from the beginning of the forecast time to the end of the forecast step. It is an accumulated variable.

Others surfaces variables

Percolation

The mass per unit area of water that drains below the deepest soil level in the model. The percolation (or drainage) is accumulated from the initial time of the forecast to the forecast time step. This variable is calculated for the natural land, including soil, vegetation and snow. (not for urban and water bodies fraction). It is an accumulated variable calculated for the natural land, including soil, vegetation and snow whereas.

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The mass per unit area of water at the surface when saturation occurs.  It is an accumulated variable calculated for the natural land, including soil, vegetation and snow.

Soil

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variables

The prognostic variables of soil temperature is provided for each soil layer. The SURFEXmodel has 14 soil layers. The vertical discretization (bottom depth of each layer in and soil moisture are represented in the model by a diffusive approach. Such a method proposes a discretization of the soil into 14 layers, resulting in a total depth of 12 m, with a fine description of the subsurface layers to capture the diurnal cycle. The vertical discretization (bottom depth of each layer in metres) is as follows: 0.01, 0.04, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 1.5, 2, 3, 5, 8, and 12 m. Soil temperature is an instantaneous variable.

Volumetric soil moisture 

12 m. Heat transfer is resolved over the total depth, while moisture transfer is resolved only over the depth of the roots, which depends on the type of vegetation and its geographical location.

Soil temperature

The soil temperature is provided for each soil layer. The SURFEXmodel has 14 soil layersThe volume concentration of liquid and ice water. The vertical discretization (bottom depth of each layer in metres) is as follows: 0.01, 0.04, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 1.5, 2, 3, 5, 8, and 12 m. The volumetric soil moisture is available for each soil layer. It is Soil temperature is an instantaneous variable.

Liquid volumetric soil moisture (non-frozen)

Volumetric soil moisture 

The It is the volume concentration of liquid and ice water only. The vertical discretization (bottom depth of each layer in metres) is as follows: 0.01, 0.04, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 1.5, 2, 3, 5, 8, and 12 m. A liquid The volumetric soil moisture is available for each soil layer. It is an instantaneous variable.

Table 3: Overview of variables available for the inland water fraction.

Liquid volumetric soil moisture (non-frozen)

It is the volume concentration of liquid water only. The vertical discretization (bottom depth of each layer in metres) is as follows: 0.01, 0.04, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 1.5, 2, 3, 5, 8, and 12 m. A liquid volumetric soil moisture is available for each soil layer. It is an instantaneous variable.

Overview of variables available for the inland water fraction.

Table 3: Overview of variables available for the inland water fraction.

Lake bottom temperature

Temperature of water at the bottom of inland water bodies (lakes). The model keeps lake depth and surface area (or fractional cover) constant in time. It is an instantaneous variable.

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Static variable do not change depending on the model initial time or the forecast length (in other words they are time-independent). These include the land-sea mask, that is the fraction of land in a given model grid box of 5.5 x 5.5 km² in units of %, and the orography in units of m. For each model grid box in CERRA-Land, 3 tile fractions are defined in units of %: (1) the fraction of inland water (lakes and rivers), (2) the fraction of urban areas, and (3) the fraction of nature, i.e. land areas that are not inland water or urban. There is no data available for the fraction of sea. The fraction data will be available directly from the climate data store website in netCDF format.

Table4: Static variable. The variables marked with * and labelled with TBD ("To Be Determined") do not have yet short

names in the WMO GRIB2 code definitions and have not been uploaded to the CDS in the first batch of released data.

Lake depth

Depth of inland water. It is defined for positive fractions only. It is a static field.

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This variable represents the fraction of natural land areas that are neither inland water nor urban in the grid-box. It takes values between 0 and 1.

Soil variables

The prognostic variables of soil temperature and soil moisture are represented in the model by a diffusive approach. Such a method proposes a discretization of the soil into 14 layers, resulting in a total depth of 12 m, with a fine description of the subsurface layers to capture the diurnal cycle. The vertical discretization (bottom depth of each layer in metres) is as follows: 0.01, 0.04, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 1.5, 2, 3, 5, 8, and 12 m. Heat transfer is resolved over the total depth, while moisture transfer is resolved only over the depth of the roots, which depends on the type of vegetation and its geographical location.

Accumulated surface fluxes

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