Some tests with a surface energy balance scheme, including a bulk parameterisation for vegetation, in a mesoscale model

Abstract

The problem of generating realistic boundary values of temperature and humidity in mesoscale models is discussed as well as the importance of allowing for non-linear interactions between the state of the surface and the atmosphere. An energy balance scheme, based on a bulk parameterisation of vegetation and simple prognostic equations for temperature and humidity of the soil interface, is presented. It is implemented in a hydrostatic, higher order closure model for the meso-γ-scale. Some tentative results are presented and critically evaluated. The presented parameterisation is very simple in its description of the interaction between plant and atmosphere, but shows the importance of such effects. Regarded as a building block in a mesoscale model, however, it is concluded that the present scheme is rather complicated. It is concluded that, although the results presented are realistic and show the importance of variable soil and vegetation types, it is highly doubtful if the presented parameterisation is useful in a wider perspective. Some of the parameterisations are less well founded from a physical point of view, and even if it were not so, the modeller will be hard put to specify all specifiable parameters and initialize all variables for any arbitrary area and event. It is thus concluded that this problem may still have to be dealt with in a simpler fashion. The question is raised if it should not be possible to obtain comparatively good results, similar to those in this paper, by simpler means.