Influence of synoptic weather events on wintertime evaporation and surface energy budget over an open water surface in Mississippi, U.S.A

Using long-term eddy covariance measurements during two winters in 2007 and 2008, we will present an analysis of how synoptic weather events significantly affect wintertime evaporation and surface energy budget over an open water surface. The measurements were conducted in the Ross Barnett reservoir (32o26'N, 90o02'W), Mississippi, U.S.A. The fetch for the eddy covariance system exceeded 2 km in all directions and the water depth is about 4 m around the flux tower. Synoptic weather events determine large-scale meteorological properties of air masses passing over water. Cold and dry air masses promote sensible and latent heat exchange between the water surface and the atmosphere. Warm and wet air masses suppress the vertical temperature and humidity gradients and dampen exchange of sensible and latent heat exchange. Therefore, day-to-day variations in sensible and latent heat fluxes are strongly influenced by synoptic weather patterns in wintertime. Analysis of meteorological data and synoptic charts indicates that there were more cold front activities in the 2007 wintertime than in the 2008 wintertime. Our results indicate that sensible and latent heat fluxes in the 2007 winter are about 27% and 36% higher than those in the 2008 wintertime, respectively. These results suggest that future potential changes in cold front activities (intensity, frequency, and duration) may lead to substantial shifts in regional energy budget and hydrological balance in the southern regions with an abundance of open water bodies (e.g., lakes, reservoirs, swamps etc).