Properties of flow and pressure over Georges Bank as observed with near-surface drifters

Abstract

During the 1995-1999 Northwest Atlantic GLOBEC project, 203 drifters drogued at nominally 10 m were deployed on or near Georges Bank. The objectives of the deployments were to characterize flow patterns and residence time properties. During all seasons, there was a tendency for clockwise flow around the bank, and this flow, along with the residence time, increased during the summer. Residence times ranged from typically 40 days during the winter to 90 days during the summer. The seasonal change in mean flow implies a role for processes beyond simple barotropic tidal rectification to be important in the dynamics. Regional subtidal frequency pressure patterns (estimated using the drifter data) dominate the sea level variability, but they play less of a role in the subtidal current variability. Instead, current variations seem to be more dominated by shorter-scale patterns and (during winter) by flow associated with the surface Ekman layer. At 10 m depth, net current variability does not change much on a seasonal basis. A few events with particularly good drifter coverage are used to illustrate the effects of a Warm Core Ring south of the bank, and of strong winter and spring storms. Copyright 2003 by the American Geophysical Union.