Wind bursts and enhanced evaporation in the tropical and subtropical Atlantic Ocean

Satellite-derived estimates of weekly latent heat flux for the tropical and subtropical Atlantic Ocean (40°S to 40°N) were calculated for a one-year period from September 30, 1996 to September 28, 1997 (52 weeks). The oceanic variables required to estimate evaporation (sea surface temperature, surface wind speed, and surface air humidity) were obtained from sensors on several polar-orbiting satellites including the European Remote Sensing satellite 2 (ERS-2), the NASA scatterometer (NSCAT), and the Special Sensor Microwave/Imager (SSM/I). During this period, high values of the weekly satellite estimates of wind speed and latent heat flux were found over the northeast and southeast trade wind regions. In these regions, the 52-week average fields showed wind speeds greater than about 7 m s1 and associated evaporation rates greater than 120 W m2. The annual cycle dominates the temporal evolution of sea surface temperature but is hardly noticeable in wind speed and latent heat flux, which are dominated by large 3-4 week fluctuations. The most significant event during our period of study was a strong northeast trade wind burst that originated near the northwest African coast in early February 1997. It persisted for five weeks as it crossed the North Atlantic Ocean and finally dissipated in the Caribbean Sea in early March 1997. In the southeast trade region, a similar but less intense period of higher flux was observed during July 1997. These large-scale wind bursts illustrate the strong role that the Atlantic trade winds play in enhancing evaporation.