Jl. Wilkin et al., PACIFIC-OCEAN HEAT-TRANSPORT AT 24-DEGREES-N IN A HIGH-RESOLUTION GLOBAL-MODEL, Journal of physical oceanography, 25(10), 1995, pp. 2204-2214
Meridional heat transport in the North Pacific Ocean in a seasonally f
orced high-resolution global ocean general circulation model is compar
ed to observations. At 24 degrees N, annual mean heat transport in the
model of 0.37 X 10(15) W is half the most recent direct estimate of 0
.76 +/- 0.3 x 10(15) W from hydrographic data. The model value is low
because the model ocean loses too little heat in the region of the Kur
oshio Current Extension. The water ventilated in this region returns s
outhward across 24 degrees N at depth between 200 m and 500 m approxim
ately 2 degrees-4 degrees C too warm. if the model surface temperature
were relaxed to a temperature adjusted for the influence of persisten
t atmospheric cooling in this region, rather than relaxed to climatolo
gical sea surface temperature, the model heat transport would improve.
Assumptions inherent in estimating meridional heat transport from hyd
rographic sections are tested by examining the model. Rather than the
abyssal circulation being steady, the model's deep western boundary cu
rrents vary seasonally to balance the seasonal cycle of Ekman transpor
t, producing a larger seasonal variation in heat transport than is gen
erally supposed for direct heat flux calculations. But the variability
is such that there is no net contribution to the mean heat transport
through a seasonal correlation between winds and surface temperature.
The use of surface temperature observed during a single hydrographic s
ection can seasonally bias an estimate of the wind-driven component of
the heat transport, so a modification is proposed to the procedure by
which compensation is made for seasonal variability in direct heat tr
ansport calculations. The most recent direct estimate was based on a s
pringtime section, for which the model heat transport would be underes
timated by about 0.05 X 10(15) W. Interannual timescale correlations i
n the transport and temperature of the Kuroshio Current contribute a n
et southward transport of some 0.07 X 10(15) W. The role of simulated
mesoscale eddies is minor. Given the comparable order of the southward
interannual heat transport and the northward seasonal bias, this pres
ent study does not suggest any significant revision to the latest dire
ct heat transport estimate for 24 degrees N in the Pacific. Other feat
ures of the model general circulation are noted, including a Kuroshio
Current transport that is stronger than observed and the persistence o
f a branch of the Kuroshio that does not separate at 35 degrees N but
continues close to the coast forming unrealistically deep mixed layers
through intense surface cooling.