Spatiotemporal variations of the surface Kuroshio east of Taiwan Island derived from satellite altimetry data

Spatiotemporal variation of the surface Kuroshio east of Taiwan Island is investigated by quantitatively analyzing 23-year(1993–2015)sea surface Absolute Dynamic Topography data.The annual mean state of the Kuroshio is shown,with a flow width ~136 km and surface transport ~7.75×10~4 m^2/s.The corresponding standard deviations of these are 28 km and 2.14×10~4 m^2/s.Results of power spectrum analysis indicate that the primary periods of Kuroshio surface transport east of Taiwan Island are 1 and 2.8 years,respectively.Spatially,the Kuroshio surface transport southeast of Taiwan Island has greater variability than that to its northeast.That transport showed strong seasonality,with a maximum 8.8×104 m^2/s in summer and minimum 7.5×10~4 m^2/s in winter,which was mainly caused by local monsoon winds.A linear long-term upward trend of Kuroshio surface transport during 1993–2015 was found,during which the mean,southeast,and northeast of the Kuroshio east of Taiwan Island increased by 0.30×10~4,0.22×10~4 and 0.36×104 m^2/s,respectively.Correlation and composite analysis show that the Philippines-Taiwan Oscillation(PTO)is important in the interannual variability of the Kuroshio.PTO-induced relative intensity of anticyclonic and cyclonic eddies is the dominant influence on the interannual variability of the Kuroshio east of Taiwan Island.

Three-dimensional numerical calculations of currents east of Taiwan Island in December 1997

Based on the wind and hydrographic data obtained from the cruise of China - Japan Cooper- ative Research on Subtropical Gyre during December 1997, the Kuroshio east of Taiwan Island and the currents southeast of the Ryukyu-gunto are computed by using three-dimensional diagnostic, semidiag- nostic and prognostic models in the a coordinate. The computed results show that: (1 ) The density and velocity fields have been adjusted when time is about 15 d, namely, the solution of semidiagnostic calcu- lation is obtained. The quasi-steady state solution has been reached after 300 d, thus and the results of prognostic calculation got. (2) From the diagnostic calculation, the following main results can be obtained-1) There is a stronger cyclonic eddy with tongue-shaped in the region south of Taiwan Island, and the Kuroshio is located east of this cyclonic eddy. Compared with the results in July 1997, the position of the main axis of the Kuroshio moves eastward. 2) There is an anticyclonic eddy south of Miyako- jima, and there is a cyclonic eddy near the middle of the southern computational boundary. 3) The upwelling dominates in an area of the Kuroshio near Taiwan Island. (3) Comparing the results of diagnostic calculation with those of semidiagnotic and prognostic calculations indicates that the hortizontal velocity fields agree qualitatively, and there is a little difference between them in quantity. For example, the maximun horizontal velocities of the Kuroshio at the sea surface at t = 0 d (diagnostic), 15 d (semiaiagnostic) and 300 d (prognostic) are 88. 6, 98. 0 and 97. 0 cm/s, respectively. As to the distributions of vertical components of velocity, there are some differences between them, which shows that the semidiagnostic and porognostic results can coincide with better the salinity and temperature distributions.