Environmental Controls on the Surface Energy Budget over a Large Southern Inland Water in the United States: An Analysis of One-Year Eddy Covariance Flux Data

Abstract

he authors analyzed the surface energy fluxes that were measured by an eddy covariance system over the Ross Barnett Reservoir in Mississippi for a 1-yr period in 2008. On a monthly basis over the course of the year, positive vertical temperature and vapor pressure differences were observed, though negative vertical temperature differences occurred occasionally during some short periods when overwater air masses were warmer than the water surface. Consequently, the unstable atmospheric surface layer (ASL) and sufficient mechanical mixing led to positive sensible H and latent ?E heat fluxes. The quantities H and ?E were distinctively out of phase with the net radiation Rn. The H and ?E from the water to the ASL was still substantial on nights with a negative Rn and in winter when Rn was very small. From February to August, approximately 60%?91% of the Rn was used for H and ?E, with the remainder being stored in the water. Fueled by the previously stored heat in the water, H and ?E exceeded Rn by almost 3 times from September to January. Nighttime evaporation represented a large loss of water (i.e., ?E = 82.8 W m?2 at night versus 91.4 W m?2 during the daytime). Intraseasonal and seasonal variations in H and ?E were strongly affected by frequent passages of large-scale air masses that were brought in by different synoptic weather systems (e.g., cyclones or anticyclones). The authors? analysis suggested that this southern reservoir responded to atmospheric forcings on both diurnal and seasonal scales in the same ways as northern lakes of comparable sizes and depths.