The Seasonal And Interannual Variation Of The Upper Kuroshio Circulation In The East China Sea And Its Relationship With Local Wind Stress

The Kuroshio is a main branch of the western boundary current in the North Pacific. It not only influences the global climate variation, but also plays an important role in regional climate of the East Asia. There are many factors influencing the Kuroshio, but the wind stress obviously is an importance one. Although the local wind stress isn't the crucial factor influencing the Kuroshio, it has importance influence on the seasonal and interannual variation of the Kuroshio currents (especially its upper circulation). In this paper based on the SODA dataset, the seasonal and interannual variation of the upper Kuroshio circulation and the local wind stress in the East China Sea (ECS) are analyzed, and the relationship between them is also detailed discussed. The following conclusions can be deduces from the results:(1) Based on GEK and CTD dataset, Ii is found that the Kuroshio in the ECS is stronger in spring and summer than in autumn and winter. There is counter current on the right of Kuroshio in the ECS. Compared the mean surface velocity of the GEK data and the temperature and salt of the CTD data with the SODA data's, the results based on SODA dataset to simulate the Kuroshio's basic pattern in the ECS is acceptable.(2) The depth of upper circulation in the ECS Kuroshio directly influenced by the local wind stress is 100m.Based on current data in the SODA dataset, the upper Kuroshio volume transport (100m) cross three sections are calculated. The transport in the ECS has certain regional difference. Compared with the transport across the three sections, it is the largest cross the PN section; secondly cross the A section (East of Taiwan Island); the smallest cross the B section (the Tokara Strait). The correlation coefficient between the interannual transport anomalies cross the PN section and the B section is larger than cross the PN section and the A section. As an example, the seasonal and interannual variation of the transport cross the PN section is studied: The transport is larger in spring and summer than in autumn and winter. The wavelet analysis shows that the primary interannual period of the transport is 2-4 years. Before the late 1970s, lower frequency period is about 20 years, but it is only about 8 years after the late 1970s.(3) Through vector EOF analysis of the wind stress in the ECS, the total contributions of the first 3 EOF modes are above 80%, so they can represent the original wind stress. The spatial distributions of the first mode indicates the variation of meridional wind stress in the ECS, the spatial distributions of the second mode indicates the variation of zonal wind stress in the ECS, the spatial distributions of the third mode indicates the anti-cyclone variation of wind stress in the ECS. But the variation of meridional wind stress is dominated. The variation of the wind stress in the ECS not only has prominent seasonal variation, but also has interannual period for 3-4 years. On the interannual scale, the variation of the wind stress in the ECS lags the variation of ENSO for 3 months. So the meridional wind stress in the ECS Kuroshio area is calculated. Its seasonal variation is very similar with the upper transport across the PN section. The wavelet analysis shows that the dominated interannual period is also 2-4 years and the decadal period is about 20 years.(4) The seasonal variation of the upper Kuroshio velocity is about 10cm/s and lags the seasonal variation of the local wind stress for 1 month. The seasonal variation of the lower Kuroshio velocity is small. The interannual variation of the upper Kuroshio velocity is about 20cm/s. The local wind stress has a close relationship with the upper Kuroshio transport cross the PN section. Its seasonal variation is very similar with the upper transport, but the lower transport cross the PN section hasn't the similarity. In monthly sequences of the correlations of the innterannual variation between the upper transport anomalies and the local wind stress anomalies the coefficient in spring and summer is larger than in autumn and winter. The wavelet analysis shows that the primary interannual period of the wind stress curl in the North Pacific is also 2-4 years, the same as the upper Kuroshio transport cross the PN section and the local wind stress. On the interannual scale, the upper transport cross the PN section lags the local meridional wind stress for 1 month and lags the wind stress curl in the North Pacific for 7 months. The correlation coefficient is about 41% and 30% respectively.