Jy. Sheng et Kr. Thompson, SUMMER SURFACE CIRCULATION ON THE NEWFOUNDLAND SHELF AND GRAND-BANKS - THE ROLES OF LOCAL-DENSITY GRADIENTS AND REMOTE FORCING, Atmosphere-ocean, 34(2), 1996, pp. 257-284
Summer surface circulation on the Newfoundland Shelf and Grand Banks i
s diagnosed from observed density profiles using the method proposed r
ecently by Sheng and Thompson (unpublished manuscript). To assess the
accuracy of the predictions they are compared against all available ne
ar-surface current measurements for the region. In accord with earlier
studies, local density gradients alone cannot account for the summer
surface circulation in this region. The surface currents diagnosed fro
m the density field are much weaker than the observations, particularl
y near the shelf break. To explain the discrepancy we use a simple inv
erse method to infer the optimal inflow boundary conditions for a baro
tropic model from the differences between the observed and diagnosed c
urrents. The surface circulation is then modelled as the sum of the di
agnosed baroclinic component and the remotely-forced barotropic compon
ent Overall the predicted circulation pattern agrees reasonably well w
ith the current observations and maps of the mean surface circulation
based on a variety of data sources. The predicted circulation pattern
has identifiable inshore and offshore branches of the Labrador Current
that split and merge as they encounter the main banks and saddles of
the region. The mean square of the observed currents (J(obs)) is reduc
ed by 52% on removal of the combined effect of local density gradients
and remote forcing. Removing the baroclinic component alone reduces J
(obs) by 40%. Our conclusion is that both remote-forcing and local den
sity gradients make significant contributions to the circulation in th
is region. For example the strong shelf-break flow on the northeast Ne
wfoundland Shelf appears to be due mainly to remote-forcing while the
circulation over Flemish Cap, and the narrow coastal jet off southeast
Newfoundland are due mainly to local density gradients.