Journal of Physical Oceanography, 34,
2, 513-525., 2004
Sverdrup Balance and the Cyclonic Gyre in the Sea of Okhotsk
K. I. Ohshima, D. Shimizu, M. Itoh, G. Mizuta, Y. Fukamachi, S. C. Riser, and M. Wakatsuchi
It is proposed that the cyclonic gyre over the northern
half-basin of the Okhotsk Sea is driven by the wind stress curl and that a major
part of the East Sakhalin Current (ESC) can be regarded as its western boundary
current. Both from the high-resolution ECMWF and Comprehensive Ocean–Atmosphere
Dataset (COADS) data, the annual mean wind stress curl is positive over the sea.
When the Sverdrup streamfunction is calculated by excluding the shallow shelves,
the streamfunction shows a cyclonic pattern over the central basin, which is
roughly consistent with the geopotential anomaly distribution from all the
available hydrographic data. Profiling floats suggest that the cyclonic gyre
extends to at least a depth of 500 m: a relatively intense southward flow (ESC)
with an average speed of approximately 10 cm s−1 near the western
boundary and slow northward flow with an average speed of approximately 2 cm s−1
in the east. Climatological data show that along zonal sections at 50°–53°N
isopycnal surfaces gradually rise from the east to west and sharply drop near
the western boundary, suggesting the Sverdrup balance. This feature persists
throughout the year. The integrated northward baroclinic transport of 3.5 Sv
along 53°N is comparable to the Sverdrup transport of 3.7 Sv, calculated from
the annual mean wind stress. Sverdrup balance appears to hold roughly in the
baroclinic field in 50°–53°N. A flat-bottom numerical model forced by realistic
wind stress reproduces well the cyclonic gyre, with the observed baroclinic
features. In the south, the anticyclonic circulation in the Kuril Basin cannot
be explained by the wind stress curl inside the Okhotsk Sea in this simplified
model.