SEASONAL AND INTERANNUAL VARIABILITY OF THE NORTH EQUATORIAL CURRENT,THE MINDANAO CURRENT, AND THE KUROSHIO ALONG THE PACIFIC WESTERN BOUNDARY

Along the Philippine coast in the western Pacific, the North Equatoria l Current (NEC) bifurcates into the northward flowing Kuroshio and the southward flowing Mindanao Current. Using both tile linear, time-depe ndent Sverdrup theory and a high-resolution, nonlinear reduced-gravity model, this study investigated the changes in the NEC-Mindanao Curren t-Kuroshio (NMK) system induced by large-scale surface wind forcings.: Using the Florida State University monthly wind ., stress data from 1 961 through 1992, we show that the seasonal bifurcation of the NEC occ urs at the northernmost position in October and the southernmost posit ion in February. While the meridional migration of the basin-wide trad e wind has a relatively small effect in shifting the bifurcation latit ude (by about 100 km), the monsoonal wind along the low-latitude weste rn Pacific is effective in inducing a large northward excursion of the NEC's bifurcation in the fall season. On the interannual timescale, t he positive wind stress curl of the trade wind tends to intensify and shifts the zero wind stress curl line northward prior to El Nino-South ern Oscillation (ENSO) events. With a lag of about 1 year this shift i nduces the bifurcation of the NEC to occur at a higher latitude. Durin g the La Nina years the NEC generally bifurcates at a lower latitude. No significant seasonal fluctuations are found in the transport of the NEC near the Philippine coast. Seasonal changes in the Mindanao Curre nt and the Kuroshio are, however, significant, and their transports te nd to fluctuate 180 degrees out of phase, due to the different speeds of the baroclinic Rossby waves at their respective latitudes. The Kuro shio (the Mindanao Current) has a seasonal minimum (maximum) transport in fall when the NEC bifurcates at the seasonally northernmost latitu de. The interannual changes in the inflow NEC are largely controlled b y the basin-wide, wind stress curl anomalies. While the quasi-biennial changes are confined only to the southern limb of the NMK system, sig nals with ENSO timescales are found to influence the midlatitude, subt ropical circulation via the Kuroshio.