On the geographic and seasonal patterns of the near-surface circulation on Georges Bank — from real and simulated drifters

Abstract

We examine the near-surface circulation on Georges Bank by comparing data collected from satellite-tracked drifters in the real ocean and data computed for simulated drifters in a virtual ocean. The observed trajectory data set was obtained from drifters drogued at 10 m during the 1995–1997 US GLOBEC Northwest Atlantic/Georges Bank field program. The simulated drifter trajectories were computed based upon the seasonal circulation as predicted by the Dartmouth Circulation Model, using bimonthly climatological forcing. The observed and simulated drifter patterns indicate well-organized anticyclonic around-bank flow on the northern flank, Northeast Peak, and southern flank throughout the year. The key to recirculation around the Bank is the seasonality of the northward flow in the Great South Channel. Winter months are characterized by little northward flow, while there is significant northward flow in the Great South Channel in summer. In late summer, both observed and numerical drifters indicate a minimum recirculation time on Georges Bank of roughly 40 days. The simulated drifter trajectories generally predict a seasonal climate consistent with the observed drifters, though the effects of weather events on the observed drifters are not captured by the numerical simulations.