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 Cooperative Research on Subtropical Gyre during December 1997,the Kuroshio east of Taiwan Island and the currents southeast of the Ryūkyū-guntō are computed by using three-dimensional diagnostic,semidiagnostic and prognostic models in the σ 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 calculation 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 obrained-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 Miyakojima,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 horizontal velocity fields agree qualitatively,and there is a little difference between them in quantity.For example,the maximum horizontal velocities of the Kuroshio at the sea surface at t=0d (diagnostic),15 d (semidiagnostic) and 300 d (prgnostic) 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 semidi-agnostic and prognostic results can coincide with better the salinity and temperature distributions.