Application of the concept of blending height to the calculation of surface fluxes in a mesoscale model

Abstract

The concept of blending height is implemented into the nonhydrostatic mesoscale transport and flow model METRAS for the calculation of grid averaged subgrid scale surface fluxes of momentum, heat and moisture over flat terrain with different land-use categories. Two-dimensional simulations including diurnal variations of the surface temperature and humidity are carried out for different horizontal resolutions of the model. Fine and coarse horizontal grid sizes are applied. The differences between the surface fluxes calculated with fine and coarse horizontal grid sizes are small for averages over the simulation domain, if convection is absent. However, for convective conditions the domain averaged surface fluxes are depending on the turbulence parameterization. If convection is inadequatly parameterized, the domain averaged surface fluxes vary with model resolution. In contrast, the application of the so-called "bottom-up/top-down"-parameterization results in mean surface fluxes independent on model resolution.

Keywords

• blending height
• nonhydrostatic
• turbulence parameterization
• horizontal grid sizes
• "bottom-up/top-down"-parameterization
• blendhöhe
• nichthydrostatisch
• turbulenzparameterisierung
• horizontalgitterweiten
• "bottom-up/top-down"-parameterisierung