Response of South Carolina continental shelf waters to wind and Gulf Stream forcing during winter of 1986

The South Carolina shelf water response to strong winter atmospheric forcing and Gulf Stream variations over the slope is discussed with the aid of a comprehensive set of atmospheric and oceanic observations made during project GALE (Genesis of Atlantic Lows Experiment). A mixed response is observed to wind and Gulf Stream forcing. Subtidal variability of inner and middle shelf waters is primarily a barotropic, forced response to coherent, synoptic scale, alongshore winds. This response is not trapped over the shelf, as has been found for other wide, non‐equatorial shelves, but is also significant at the shelf edge, possibly because of the comparable widths of the shelf and slope. The outer shelf also shows a significant Gulf Stream influence. The Gulf Stream appears to have two preferred position modes, either onshore, with the stream flowing over the Charleston bump and along the shelf break, or offshore, when the stream can be located up to 100 km east of the shelf break; transition between the two states is rapid. Subtidal variability in the outer shelf is dominated by weekly period frontal eddies and meanders when the stream is in an onshore mode, and by persistent southward flow when the stream is offshore. This southward flow is produced by enlarged cyclonic eddies with upwelled centers located over the slope between the offshore Stream and the shelf edge, sometimes referred to as the Charleston gyre. Positive mean alongshore sea level slopes at the shelf edge, due to the persistence of the cyclonic gyres, are geostrophically balanced by mean onshore flow, which transports upwelled waters onto the shelf, enhancing the biological productivity of the area relative to other regions of the South Atlantic Bight.