Effect of atmospheric stability on evaporation over a large reservoir

Abstract:

Water reservoir loses water through evaporation. Atmospheric stability promotes or suppresses turbulence and energy exchange between the water surface and the atmosphere and could affect evaporation rates. We analyzed the datasets collected from an eddy covariance station at the all-year ice-free Ross Barnett Reservoir, Mississippi from August 2007 to March 2008 to uncover the effect of atmospheric stability on evaporation. Results indicate key parameters that affect evaporation (latent heat flux, LE, proportional to evaporation) are (in sequence of significance) 1) presence of cold fronts (dry and cold northern winds), 2) water vapor pressure difference between the water surface and the atmosphere, 3) mean wind speed, and 4) atmospheric stability. Generally, LE is small in stable atmosphere and increases steadily when transitioning to unstable atmosphere. Within either unstable or stable subcategories, trends of LE become less obvious, with increasing to decreasing trends with more stable or unstable conditions. Vapor pressure difference plays an important role to LE in this case in contrast to wind speeds. Insurgence of cold fronts - synoptic weather processes - substantially alters turbulence and heat exchanges between water and atmosphere, masking the effect of stability on evaporation.