On Steady Response of a Ventilated
Thermocline to Enhanced Ekman Pumping
Atsushi Kubokawa and Shang-Ping Xie
Graduate School of Environmental Earth
Science, Hokkaido University, Sapporo, Japan
J. Oceanography, 58, 565-575.
Abstract. Steady response of the ventilated thermocline
to an increase in Ekman pumping is investigated, with a focus on the effect of
the mixed layer depth distribution on the subsurface density anomaly. The mixed layer is assumed to be deep in the
northwest and shallow elsewhere with a narrow transition zone separating the
deep and shallow mixed layer regions.
At the intersection of this narrow transition zone and the outcrop line,
low potential vorticity fluid is subducted and ventilated into the
thermocline. In such a situation, an
enhancement of the Ekman pumping confined to the northern subtropical gyre
leads to pronounced subsurface cold anomalies in the southern subtropics that
is free of anomalous forcing. These
density anomalies are much greater than those when either the mixed layer depth
is zonally uniform or the Ekman pumping is enhanced in the whole subtropical
gyre. They are caused by anomalous changes
in the trajectory of the low potential vorticity fluid in response to anomalous
Sverdrup flow.