To examine the potential use of climate models for the simulation of winter season precipitation, topography that is more highly resolved than commonly used for global climate models (about 200 km) is needed. Hahmann and Dickinson (2001) introduced a land surface model interface, the "fine-mesh model", which represents sub-grid scale land surface heterogeneity by a sub-mesh imposed on each atmospheric model grid. A water and energy-conserving scheme disaggregates atmospheric conditions to the fine-mesh model grid and aggregates surface fluxes back to the atmospheric grid. The fine-mesh model at a resolution of 0.5° is coupled to the NCAR Community Climate Model Version 3 (CCM3). The next step in the development of the fine-mesh model is to introduce physically based parameterizations that allow for non-uniform distribution of the atmospheric forcing. The impact of the introduction of topographic slopes and aspects in the fine-mesh model, in terms of their effect on surface radiative fluxes, is presented in this paper.

The American Southwest depends on seasonal alpine snowpacks for a significant fraction of its annual water needs. In addition, snowpacks over this region have been linked to the strength of the North American monsoon system and therefore summer precipitation over this region. The complex terrain of the western U.S. provides a natural testbed for studying the impact of the introduction of topographic characteristics in the simulation of its climate. Simulations using CCM3 coupled to the fine-mesh model (with and without the introduction of topographic slope and aspect) are evaluated in terms of their simulation of snow depth and cover, and in particular to the timing of springtime streamflows.