SEASONAL TRANSPORT VARIATIONS OF THE KUROSHIO - AN OGCM SIMULATION

Numerical simulation is performed using a high-resolution ocean genera l circulation model to investigate seasonal variations of the Kuroshio transport. The simulated velocity profiles of the Kuroshio agree surp risingly well with ADCP observations and dynamic calculations. The ann ual mean of the model Kuroshio transport relative to 700 m across the PN line near the Nansei (Ryukyu) Islands is about 25 Sv (Sv = 10(6) m( 3) s(-1)), which is almost the same with the estimate based on the lon g-term hydrographic observations. The model transport variations acros s the PN line are also almost the same as the observation; the transpo rt shows a weak maximum in summer and a weak minimum in winter. Althou gh the Sverdrup balance is valid in the broad interior of the basin, i t fails to predict the variations as well as the transport of the Kuro shio south of Japan due to existence of the Kuroshio recirculation. Th e above discrepancy between the Sverdrup theory and the model (observa tions, as well) is studied in detail by analyzing the torque balance. In winter the Kuroshio transport across the PN line is much smaller th an expected from the Sverdrup theory because the topographic control p revents the western boundary current from intruding west of the contin ental slope near the Nansei Islands. The current over the slope legion changes its direction from winter to summer due to anticyclonic eddy activity related to the joint effect of baroclinicity and bottom topog raphy. The deep northeastward current over the slope in winter is canc eled in summer by the eddy activity so that the interaction between th e continental slope and the current is much reduced. Since the same ed dy activity intensifies the Kuroshio recirculation, the Kuroshio trans port across the PN line in the East China Sea is increased in summer. The present study demonstrates that comparing model results with obser vations requires a model resolution suitable enough to resolve locatio ns of observations as well as essential dynamics related to the intera ction between baroclinic ocean currents and bottom topography.