PACIFIC-OCEAN HEAT-TRANSPORT AT 24-DEGREES-N IN A HIGH-RESOLUTION GLOBAL-MODEL

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.