Upper-slope jets and gulf stream filaments inshore of the Charleston Bump during winter 2012

Abstract

A 3-month-long field program conducted in winter 2012 inshore of the seaward deflection of the Gulf Stream at the Charleston Bump observed several 7-21-day periods of strong (> 0.5ms-1) equatorward alongshelf flow over the upper continental slope. In sea surface temperature images, these phenomena resemble and appear linked to warm filaments, features known to be associated with meanders of the Gulf Stream as it traverses the southeast coast of North America. However, the character of these upper-slope features differs from previous descriptions of filaments, hence we describe them as ''upper-slope jets.'' We document the characteristics of the jets, which are approximately 30 km in width, centered on the 200-m isobath, with a maximum temperature variation at depth, and reasonably long-lived. Southwestward flow within the jet extends to 200m and is in approximate thermal wind balance below a surface mixed layer. Maximum transport is estimated to be about 2.0 Sv (1 Sv ≡ 106m3 s-1), driving a net equatorward along-shelf velocity over the deployment period. For this time period, at least, the jets form the equatorward flow of the shoreward flank of the Charleston Gyre. We suggest the features resemble the Pinocchio's Nose Intrusion recently described by Zhang and Gawarkiewicz. Large-amplitude meander crests with sufficiently strong curvature vorticity are a plausible source of initiation of the upper-slope jets.