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Description of the data provided by climate models

Many different variables

State-of-the-art climate models produce enormous amounts of data, both in terms of the richness of different variables as well as the volume of data for each variable. To get a better overview of what is available, some databases group the variables. into different categories.

For example, the CMIP5 database of GCM data divides the variables into different realms: aerosols, atmosphere, land surface (vegetation and soil), land ice, ocean, ocean bio-geochemistry, and sea ice.

Another distrinction ís based more on the model components. The atmospheric component of a climate model, whether a GCM or an RCM, has a lowest model level of the grid at several tens of metres above the land surface. A specific surfare component of the model handles the interaction between the land surface, vegetation and atmosphere. Because of this, a distinction is often made between atmospheric variables that are derived from the grid representing the atmosphere, and surface variables that are produced by the surface model (surface scheme). Similarly, when an ocean model component is available a distinction is often made between ocean variables derived from the 3-d ocean grid and sea-ice variables from the sea-ice submodel.

‘Tiled’ land surface subdivision

Often the vegetation and landcover/landuse exhibits considerable local variation within one gridcell. To account for the different energy balances of these different environments some models' surface scheme have different tiles within a gridcell. In these each gridcell is divided into several tiles according to the percentage of a few broad vegetation/land cover classes. For example, there might be separate tiles for forests, lakes, urban area, open land, and so forth. The number of different tiles as well as the level of detail in the land cover classification differs between different models. The individual energy balances of each tile is then agggregated to a gridcell average.

 

 

The principle of a state-of-the-art land tiled land surface scheme. For each atmospheric gridbox there are different tiles for each principal landuse/landcover category. The area of each tile is proportional of the total area in each gridbox. In this particular example (the Surfex system) the tile "Nature" is further divided into patches of different vegetation sub-classes. Image source: CNRM/Météo France.

One of the uses of a tiled land surface gridcell is to improve the representation of the surface energy balance of an ‘open land’ land cover class. As standard meteorological stations are located in open areas, this land cover class may provide surface variables that are be more representative of meteorological observations than the variables related to some average land cover class.

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