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In the H-TESSEL
scheme (Hydrology-Tiled ECMWF Scheme for Surface Exchange over
Land) the main types of natural surfaces found over land are
represented by a "mosaic" approach. In other words, each
atmospheric model grid-box is in contact and exchanges energy and
water with up to 6 different types of parcel or "tile" on the
ground. These are: bare soil, low and high vegetation, water
intercepted by leaves, and shaded and exposed snow.
Each land-surface
tile has its own properties, describing the heat, water and
momentum exchanges with the atmosphere; particular attention is
paid to evaporation, as near-surface temperature and humidity are
very closely related to this process.
The soil (with its
four layers) and the snow-pack (with one layer) have dedicated
physical parametrizations, since they represent the main land
reservoirs that can store water and energy and release them into
the atmosphere in lagged mode.
Finally, the
vegetation seasonality is described by the leaf area index (LAI)
from climatalogical data. The LAI describes the growing, mature,
senescent and dormant phases of several vegetation types in
H-TESSEL (four types of forests and ten types of low
vegetation).
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