Three dimensional diagnostic, semidiagnostic and prognostic calculations of current in the East China Sea in April of 1994

Three dimensional diagnostic, semidiagnostic and prognostic models in the a-coordinate are used to compute the current in the Fast China Sea with wind and hydrographic data obtained from the investigation of ocean fluxes in the East China Sea during the cruise of April 1994.The computed results show that:the density and velocity fields and so on have been adjusted when time t≈23 d, i.e., the solution of semidiagnostic calculation has been obtained.The quasi-steady state solution also has been reached after about 60 d.Comparing the results of diagnostic calculation with those of semidiagnostic and prognostic calculations, it is found that they agree qualitatively For example, they all show that:(1) The Kuroshio flows along the shelf break of 200~1 000m isobaths; (2) In the southeastern part of the computational region there is a stronger counter-current with an anticyclonic eddy; (3) The volume transport through Section lPN is about 30×10⁶m³/s and so on.However there are some quantitative differences between them.For example, (1) For the semidiagnostic results the Kuroshio current is stronger and clearer than that for diagnostic results and the Kuroshio width is more narrow than that for diagnostic results.This shows that the semidiagnostic calculation can better reflect the topography effect; (2) In most computed region the vertical component of velocity intensifies for semidiagnostic result, especially on the shelf break.Comparing the results of semidiagnostic calculation with those of prognostic calculation, they agree qualitatively, and also agree quantitatively in the middle of computed region.