Simulation and Sensitivity in a Nested Modeling System for South America. Part I: Reanalyses Boundary Forcing

A regional climate model driven by reanalyzed atmospheric forcing is used to investigate 1) the large-scale circulation anomalies that were driven by sea surface temperatures (SSTs), which resulted in extreme rainfall anomalies during January–May 1983 (dry) and 1985 (wet) in tropical South America; 2) the effects of vegetation and soil moisture in the interior Amazon basin on regional circulations, moisture transport, and rainfall; and 3) the sensitivity of regional model results to domain size. Seasonal integrations demonstrated that by prescribing observed SSTs and applying reanalyses-derived forcing along the boundaries of the control domain, the regional climate model (RegCM) was able to simulate the dramatically different large-scale circulations in the two years, as well as the resulting rainfall differences. Thus, the large-scale forcing apparently has a first-order effect on the region. The regional model shows reduced rainfall in the western Amazon compared with observed estimates that a...