A climatology and analysis of evaporative sources of rainfall over the Mississippi Basin

A quarter-century of hourly observed precipitation data, and NCEP reanalyses are being used to create a data set of the surface sources of moisture supplying rainfall during the spring and summer over the Mississippi River Basin. A quasi-isentropic back trajectory algorithm is used to determine the likely evaporative source regions. This work expands upon previous work which focused on only a few specific years. We can now describe the climatological evolution of sources and sinks in the atmospheric hydrologic cycle during the warm season, and examine interannual variability. The degree and variability of moisture recycling within the Mississippi Basin and several sub-basins is also being examined. Serial and cross correlation analysis are being performed among source regions in an effort to determine patterns and look for precursors to extreme hydrologic events. In addition, we are also examining how errors in the specification of surface evaporation, a poorly described quantity, affect the determination of source regions.