Miller, A. J., D. R. Cayan and W. B. White, 1998:
A westward-intensified
decadal change in the North Pacific thermocline and gyre-scale
circulation
Journal of Climate, 11, 3112-3127.
Abstract.
From the early 1970's to the mid-1980's,
the main thermocline of
the subarctic gyre of the North Pacific Ocean
shoaled
with temperatures at 200-400m depth cooling by 1-4$^{\circ}C$
over the region.
The gyre-scale structure of the shoaling is quasi-stationary
and intensified
in the western part of the basin north of 30N, suggesting
concurrent changes in gyre-scale transport.
A similar quasi-stationary cooling in the subtropical gyre
south of 25N is also observed but lags the subpolar
change by several years.
To explore the physics of these changes, we examine
an ocean model forced by observed wind stress and heat flux
anomalies from 1970-1988 in which we find similar changes in
gyre-scale thermocline
structure.
The model current fields reveal that the North Pacific subpolar
and subtropical gyres
strengthened by roughly 10\% from the 1970s to the 1980s.
The bulk of the eastward flow of the
model Kuroshio/Oyashio Extension returned westward via the
subpolar gyre circuit, while
the subtropical gyre return flow along 20N lags the subpolar
changes by several years.
We demonstrate that the model thermocline cooling and increased
transport
occurred in response to decadal-scale
changes in basin-scale wind stress curl
with the quasi-stationary oceanic response
being in a time-dependent quasi-Sverdrup balance over much of
the basin east of the dateline.
This wind-stress curl driven response is quasi-stationary
but occurs in conjunction with a propagating temperature anomaly associated
with subduction in the central North Pacific
that links the subpolar and subtropical gyre stationary
changes
and gives the appearance of circumgyre propagation.
Different physics evidently controls
the decadal subsurface temperature
signal in different parts of the extratropical North Pacific.
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