An Investigation Of Frontal Processes In The Taiwan Strait During Winter And Spring

In cold seasons(winter and spring),a density front in the Taiwan Strait is formed as the southward-flowing,cold and fresh China Coastal Current interfaces with the northward-flowing,warm and saline Taiwan Warm Current which is mixed with South China Sea Warm Current extension and Kuroshio.According to the observation data,the formation of the front lags its main forcing factor,the northeast monsoon,by 2~3 months.The evolution of horizontal and vertical structures of the Zhe-Min coastal front both experience obvious seasonal variation,but are not synchronized.The front is formed on the surface first and subsequently in the subsurface.There are also obvious seasonal differences in the corss-fontal structure.In winter and spring seasons,the west side of the front is cold and fresh,while the east side is warm and salty.Therefore,temperature and salinity are mostly compensated over the entire cross-front section except the frontal zone.In addition,the short-time scale variation 0(1 d)of the vertical structure and location of the front is due to wind and tides.Submesoscale characteristics are also examined for different types of the front in terms of the vertical structure.Despite the individual dynamical features,the probability density functions of vorticity,divergence and horizontal strain rate at the frontal area are generally close to a normal distribution for all types of the front.On the east side of the front,the water mass tends to be unstable,whereas the instability mainly occurs on the surface or at the bottom on the west side.There is indication of symmetry instability occuring in the frontal zone.