Observations of East Coast upwelling conditions in Synthetic Aperture Radar imagery

Seasonal coastal upwelling in the U.S. Mid-Atlantic coastal ocean normally occurs during the summer months because of generally alongshore southerly w ind episodes. Southerly winds force an offshore surface Ekman flow over the inner continental shelf. Colder and nutrient-rich waters from below upwell toward the surface replacing offshore-homing surface waters. Synthetic Ape rture Radar (SAR) observations from the European Remote Sensing (ERS) satel lite ERS-2 before and after upwelling-favorable mind episodes in early summ er 1996 along the New Jersey coast are presented here. Lower backscatter co nditions appearing in the SAR imagery after the onset of upwelling demonstr ate the influence of the upwelling regime on the sea surface roughness. Sat ellite sea surface temperature (SST) observations and in-situ sea temperatu re vertical profiles confirm upwelling conditions, Three key mechanisms are suggested to explain the lower radar returns observed under upwelling cond itions, an increase in the atmospheric marine boundary layer stability, an increase in the viscosity of surface waters, and the presence of biogenic s urfactants in the upwelling region.