Drifter Event D.

A succession of three strong winter storms passed Georges Bank during
February 25 though March 10, 1996.  The first storm caused sustained
winds (0.2-0.6 N/m^2) towards the southeast during January 25-28, and
was followed by two days of weaker southeast winds (0.1-0.4 N/m^2).  The
second storm produced sustained winds (0.2-0.8 N/m^2) towards the
eastnortheast during March 2-6.  The third storm produced southwest to
southeast winds (0.2-0.6 N/m^2) during March 7-10.

During this 14-day period, seven drifters initally located within the
60-m isobath on Georges Bank were advected to the south and southeast
into deeper water over the outer shelf and slope on the southern flank
(Figure D1).  An eigth drifter starting on the northwest flank was
carried across the southwestern crest of the bank to almost the 60-m
isobath on the southern flank. Seven of these eight drifters continued
towards the southwest along the southern flank, while the drifter that
started at the 60-m isobath on the southern flank was carried offbank
and shortly entrained in a warm-core ring.  The drifter starting on the
Northeast Peak was also carried eastward offbank into the slope water
and lost to the bank.

This example illustrates three features of the near-surface Lagrangian
flow on the bank during weak stratification.  First, a short sequence of
strong southeast and eastward wind events can move water over the crest
to the southern flank (deeper than the 60-m isobath), with some of the
crest water being carried offbank into the slope water.  (This example
is similar to the January-February 1995 already described.)  Second,
during strong sustained winds, the near-surface flow over much of the
bank is spatially coherent, i.e., the flow is roughly in the same
direction with similar speeds during the strongest wind forcing.  Third,
the near-surface flow over the southern flank can be reversed, i.e,
directed towards the east and northeast during strong eastward wind
forcing.

Fig. D1. Drifter tracks and wind stress for February 25 - March 16,
1996. Each panel shows drifter tracks over a 5-day period, starting on
February 25.  The 5-day average wind stress vector is shown in the upper
right of each panel. For comparison, a 0.2 N/m^2 east wind stress vector
is shown in the lower right of each panel.

[use gb_plotD to make figure]