Seasonal And Interannual Variabilities Of The North Equatorial Current Bifurcation And The Indonesian Throughflow And Their Correlation

Based on monthly mean Simple Ocean Data Assimilation (SODA) product (1958-2007), the major features, seasonal and interannual variabilities of the North Equatorial Current (NEC) bifurcation and the Indonesian Throughflow (ITF) volume transport are systematically studied. And In this premise condition, the seasonal and interannual variabilities correlation between the NEC bifurcation latitude and ITF transport are further discussed by the canonical correlation analysis method.The seasonal variabilities of the NEC bifurcation latitude (upper465meters), NEC-Kuroshio-Mindanao Current (NKM) system volume transport and ITF volume transport show that:the annual mean latitude of the NEC bifurcation occurs at about14.33°N, the southernmost latitude of the NEC bifurcation at upper465m is about13.8°N in June, and the northernmost latitude is about15°N in December. The NEC and Mindanao Current (MC) both have a seasonal maximum (minimum) volume transport in May (September). The seasonal variation of ITF volume transport occurs at the maximum in the northern hemisphere summer and the minimum in winter, and the Makassar Strait as the most important in flow channel of the ITF, its maximum (minimum) volume transport is about10.09Sv (4.83Sv) in August (December), the annual average of the volume transport is about7.75Sv.Canonical correlation analysis among the seasonal variabilities of the NEC bifurcation latitude, NEC volume transport and the ITF volume transport suggest that: when the NEC bifurcation moves to the south, the ITF volume transport increases, and vice versa. The seasonal variabilities of the NEC bifurcation latitude are negatively correlated with those of the NEC volume transport, and their negative correlation coefficient reached the maximum of-0.92when the NEC volume transport led the NEC bifurcation latitude by2months. With a lag of about3months, the NEC volume transport is positively correlated with the ITF volume transport, and their correlation coefficient reached the maximum of0.93. The seasonal variabilities of the NEC bifurcation latitude are negatively correlated with those of the ITF volume transport, and their negative correlation coefficient reached the maximum of-0.86when the NEC bifurcation latitude led the ITF volume transport by1month. The50years SODA product is used to investigate the interannual variabilities of the NEC bifurcation latitude (upper465meters), NKM system volume transport and ITF volume transport. The correlations among the ITF volume transport, the El Nino-Southern Oscillation (ENSO) events and the Indian Ocean Dipole (IOD) events show that:The interannual variabilities periods of the NEC bifurcation latitude and the ITF volume transport are about2-7years, and their periods before1979are smaller than those after1979. During the El Nino years the NEC generally bifurcates at a lower latitude, the volume transport of the NEC, the MC and the ITF are decreased; However during the subsequent La Nina years, the NEC generally bifurcates at a higher latitude, the volume transport of the NEC, the MC and the ITF are increased, the change of Kuroshio volume transport is less significant than those of the NEC, the MC and the ITF. Interannual variabilities of the ITF transport are mainly under the influences of the Pacific ENSO signal, however, during some special years (for example,1994), IOD signal is more significant than other factors which affect the ITF volume transport.Through the canonical correlation analysis between the interannual variabilities of the NEC bifurcation latitude and the ITF volume transport, the calculation results suggest that:In the first decades (1958-1978), the interannual variabilities of the NEC bifurcation latitude are negatively correlated with those of the ITF volume transport, and their negative correlation coefficient reached the maximum of-0.36when the NEC bifurcation latitude led the ITF volume transport by1month. From1979-2007, the interannual variabilities of the NEC bifurcation latitude are negatively correlated with those of the ITF volume transport, and their negative correlation coefficient reached the maximum of-0.65when the NEC bifurcation latitude led the ITF volume transport by10month. Overall, the interannual variabilities of the ITF volume transport lag the variabilities of the NEC bifurcation latitude, moreover, in recent30years, their negative correlations are more remarkable than before.