Downward Flux of Moisture over the Ocean

Over the world's oceans a large fraction of the energy sun's energy reaching the surface is consumed by evaporation. In general, the molecular and turbulent transport of the resulting water vapor (i.e., the latent heat flux) is directed from the ocean to the atmosphere. The moisture flux and turbulent transport are complementary processes since the moistening of the near surface air provides a mechanism for the buoyant production of turbulent kinetic energy. However, the analysis of several buoy-based data sets taken in coastal regions predict a flux of moisture from atmosphere to ocean based on fluxes derived using bulk formula (Beardsley et al., 1997). This type of situation occurs when warm, moist air is advected over cooler water resulting in a specific humidity aloft that is greater than its surface value. For example, these conditions are commonly found at the northern edge of the Gulf stream in southeasterly flows, which carry warm moist air over the cooler shelf waters. This abstract presents several data sets where direct covariance flux estimates show a downward flux of water vapor under these conditions. It compares these estimates with bulk derived fluxes and shows that the bulk estimates tend to overestimate the flux in these conditions. The abstract explores several hypotheses to explain this discrepancy, and improve the bulk parameterization of the flux.