1Intercomparison of Water and Energy Budgets for Five Mississippi Sub-basins between ECMWF Reanalysis (ERA-40) and NASA-DAO fvGCM for 1990-1999.

Abstract. Using monthly means for 1990-1999, we assess the systematic biases in temperature and humidity, and the surface energy and water budgets of both ERA-40, and the climate of the NASA-DAO atmospheric finite-volume general circulation model (fvGCM) for five Mississippi sub-basins. We compare ERA-40 and the fvGCM with basin averages of surface observations of 2temperature, humidity and precipitation, the river basin estimates for the hydrological balance from Maurer et al. [2002], and the International Satellite Cloud Climatology Project (ISCCP) retrieved skin temperature and surface radiation fluxes. We show the role of the soil water analysis in ERA-40, which generally supplies water in summer and removes it in winter and spring. The ERA-40 snow analysis increments are a significant contribution to the (smaller) frozen water budget. Compared with National Climate Data Center (NCDC) observations of screen temperature, ERA-40 generally has a relatively small (1K) positive temperature bias in all seasons for the Mississippi basins, while the fvGCM has a large cold bias in temperature in winter. The ISCCP skin temperature estimate is generally high in winter and a little low in summer, compared to ERA-40 and the NCDC screen level temperature. For the western basins, summer precipitation is high in the fvGCM, while for the eastern basins it is high in ERA-40 (i