Diagnosing warm season precipitation over the GCIP region from a GCM and reanalysis

A 45-year simulation using a global general circulation model (GCM), the Na tional Center for Atmospheric Research (NCAR) Community Climate Model versi on 3 (CCM3), forced with observed sea surface temperatures (SST), and 39 ye ars of global National Centers for Environmental Prediction (NCEP) reanalys es were analyzed to determine Mississippi River basin warm season (May, Jun e, July or MJJ) wet and dry year composites in the water and energy budgets . Years that have increased MJJ soil moisture over the Global Energy and Wa ter Cycle Experiment (GEWEX) Continental-Scale International Project (GCIP) region also have high precipitation, lower surface temperature, decreased Bowen ratio, and reduced 500-hPa geopotential height (essentially reduced M JJ ridging). The reverse is true for years that have reduced MJJ soil moist ure. Wet years are also accompanied by a general increase in moisture trans port from the Gulf of Mexico into the central United States. There is some indication (though weaker) that soil moisture may then affect precipitation and other quantities and be affected in turn by 500-hPa geopotential heigh ts. The correlations are somewhat low, however, demonstrating the difficult y in providing definitive physical links between the remote and local effec ts. Analysis of two individual years with an extreme wet event (1993) and a n extreme dry event (1988) yields the same general relationships as with th e wet and dry composites. The composites from this study are currently serv ing as the basis for a series of experiments aimed at determining the predi ctability of the land surface and remote SST on the Mississippi River basin and other large-scale river basins.