Abstract

The goal of our research is to investigate the roles of land-surface vegetation, soil moisture content and topography, in regional hydrologic cycle and its interannual variability using satellite-observed land-surface data in conjunction with global and regional atmospheric models interactively coupled with advanced land-surface models (LSMs). We will focus on the effects of land-surface processes on regional hydrologic cycles in the United States, especially in the southwestern region, by nesting a regioanl-scale atmospheric model within the UCLA-AGCM. The focus of regional study includes a possible link between winter precipitation and summer monsoon through snow cover and SMC, the effects of local land-surface forcing in shaping the regional circulation, and the role of significant terrain (the Sierra Nevada and the Sierra Madre) in low-level moisture transport, in the southwestern US.

We have analyzed a 20-year simulation performed with the UCLA AGCM in which climatological SSTs are used as the lower boundary condition. The precipitation difference pattern produced by the AGCM between wet and dry summer monsoons are similar in many aspects to the observed. However, the simulated amplitudes are much smaller than the observed. Another AGCM simulation using observed SSTs as lower boundary condition produces similar results. Those preliminary results imply a significant role for the land-surface, including sub-grid topography.

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