(Woods Hole Oceanographic Institution, 1978-07)
Saunders, Peter M.
Employing one million ship reports gathered in the years 1941-72 seasonal averages of the wind stress
and its standard deviation have been computed for the shelf region of the eastern North American continent
(out to a depth of 200 m). A drag coefficient is assumed which increases with wind speed, from
l.OXl0- 3 at 5 m s-1 to 2.3Xl0-3 at 25 m s-1. Atmospheric stratification is taken into account but its
effect is shown to be small.
In the summer season the 32-year climatological wind stress is toward the northeast, having a magnitude
close to 0.25 dyn cm-2 throughout the entire shelf region. In the three other seasons the stress is
directed toward the south and east being strongest in winter (1-1.5 dyn cm-2) and weakest in fall
(0.25-0.5 dyn cm-2). In addition to the expected increase in magnitude with increasing latitude remarkable
small-scale variability occurs. An offshore increase in stress is widespread and dominates the mid-Atlantic
Bight; in winter the stress there increases from 0.5 to 1.0 dyn cm-2 in going 200 km offshore.
In the Gulf of Maine and especially in the Gulf of St. Lawrence local maxima occur; the tail of the Grand
Banks 500 km from shore shows a minimum. Probably much of this variation is associated with the
intensity (and frequency) of cyclonic activity rather than directly with changes in friction at the underlying
surface. Some oceanographic consequences are commented on but the computations are principally
intended as a data source for further research