Parameterization of Turbulent and Mesoscale Fluxes for Heterogeneous Surfaces

Abstract

Improved parameterizations for turbulent surface fluxes over inhomogeneous terrain at several scales of heterogeneity are developed, and mesoscale numerical model results are used to evaluate them. The extension to the mosaic method, which uses stability corrected logarithmic profiles to calculate local wind speed, air temperature, and specific humidity estimates at the reference level over each surface cover, gave promising results for the larger scales of surface heterogeneity. A simple temperature adjustment method is also proposed as an extension to the basic mosaic method. At smaller scales of heterogeneity, it was shown that further improvements for the parameterization of momentum transfer are needed. These are likely to be carried out by introducing mechanisms to incorporate the effects of form drag in conjunction with the ?three-resistance? model. Based on similarity theory, simple parameterization schemes for the mesoscale heat fluxes are proposed. The parameterizations are validated with several surface and atmospheric conditions, and they turn out to be quite robust.