East Coast upwelling signatures in synthetic aperture radar imagery

Seasonal coastal upwelling in the U.S. Mid-Atlantic region occurs normally during the summer months because of generally northward alongshore wind episodes. These winds force an Ekman offshore surface flow over the inner continental shelf. Colder and nutrient-rich waters from below move toward the surface replacing the offshore flowing surface waters. ERS-2 synthetic aperture radar (SAR) observations before and after upwelling favorable winds along the coast of New Jersey in early summer 1996 are presented. Upwelling conditions are confirmed from both in-situ and sea surface temperature satellite data. The appearance of a low backscatter region on the SAR imagery suggests the influence of the upwelling regime on the sea surface roughness. In particular, the abundance of surface slicks observed by SAR along the coast is consistent with enhanced biological activity resulting from enhanced nutrient availability in the upwelled waters.