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The energy balance equation

The surface energy balance equation is the major interaction point between the LSS and the GCM. Solving it is the most important component of any land-surface scheme as it closes the energy balance at the lower boundary of the atmosphere and determines the temperature of the surface with which the atmosphere is in contact. Implicitly it also defines the surface with which the atmosphere interacts. This definition differs between LSSs and can be the surface of the ground (a ``layer'' of infinitesimal thickness at the surface/atmosphere interface) or some level within the canopy. In the following no assumptions are made on this definition, thus ensuring the generality of the discussion. In this section we will try and define the interface by discussing the elements of this equation.

The surface energy balance equation may be written for a ``layer'' at the surface in contact with the atmosphere as:

  equation63

Here tex2html_wrap_inline1117 is the temperature representative of the surface ``layer'' (Hereafter surface temperature), and tex2html_wrap_inline1119 the ``layer'' heat capacity per unit area. Note that the heat capacity may become very small as the thickness of the ``layer'' tends towards zero. tex2html_wrap_inline1121 is net long-wave radiation at the surface, tex2html_wrap_inline1123 net short-wave radiation at the surface, LE latent heat flux, H sensible heat flux and G the ground heat flux. All fluxes are positive downward. For each of these five fluxes we need to determine its relation to the atmosphere and which of its components need to be calculated by the land-surface scheme.



POLCHER Jan
Fri Mar 6 16:09:11 MET 1998