Seasonal Variability And Its Mechanisms Of Kuroshio Intrusion Into The Taiwan Strait Using The Lagrangian Method

The high temperature and high salinity of the Kuroshio water has an important influence on the circulation structure and ecosystem of the Taiwan Strait.The Kuroshio intrusion to the Taiwan Strait has attracted wide attention both at home and abroad.Most of studies on the Kuroshio intrusion into the Taiwan Strait are the analysis based on water temperature and salinity by Eulerian method,but the analysis by Lagrange method is less.In addition,the existing studies only pay attention to the possibility of the Kuroshio intrusion from the southern Taiwan Strait and never consider the possibility of the intrusion from the northern Taiwan Strait.The purpose of this paper is to explore the possibility of the Kuroshio intrusion from the northern Taiwan Strait and the seasonal variations of the Kuroshio intrusion into the Taiwan Strait in various ways,using the satellite-tracked sea surface drifter trajectory data and tracer particle test results by LTRANS(Lagrangian Transport model).According to the test results,we select the typical process of the Kuroshio intrusion into the Taiwan Strait,and then we analyze the role of wind field in the Kuroshio intrusion into the Taiwan Strait,combining with the long time series of HYCOM+NCODA Reanalysis data and ERA-Interim wind field data.Based on the statistical analysis of the sea surface drifters entering the Taiwan Strait during 1989 to 2015,we find some phenomena.In spring,the eastern Taiwan Strait is occupied by northward flow.The Kuroshio intrusion is mainly along the eastern Taiwan Strait and the intrusion by looping path is less than other seasons.There is no Kuroshio intrusion from the northern Taiwan Strait.In summer,the south and north of Taiwan Strait are both not intruded by Kuroshio.The Taiwan Strait is occupied by the South China Sea water and some water from the South China Sea can enter the western edge of the Kuroshio.The south and north of Taiwan Strait are affected by the Kuroshio water both in autumn and winter.In autumn,a large number of drifters from the Luzon Strait invaded the Taiwan Strait from south to north.The Kuroshio water invaded into the continental shelf of the East China Sea in the northeastern of Taiwan Island and the Kuroshio flows along the coast of China from north to south into the Taiwan Strait.Compared with autumn,the Kuroshio intrusion from the south of Taiwan Strait increases significantly,but the Kuroshio water are blocked in Penghu channel.In the northeast of Taiwan Island,the trajectory of the Kuroshio intrusion is closer to the north shore of Taiwan Island and then the Kuroshio water intrude from north to south along the eastern Taiwan Strait.We initially obtain the seasonal characteristics of the Kuroshio intrusion into the Taiwan Strait from the statistical analysis of drifters trajectory.But in order to further explore the seasonal characteristics of the different paths of the Kuroshio intrusion into the Taiwan Strait,we simulate the Kuroshio intrusion from the south and north of Taiwan Strait by LTRANS.The results confirm that the Kuroshio water can both intrude from the south and north of Taiwan Strait.Both intrusions have obviously seasonal difference.There are three main paths of the intrusion from the south of Taiwan Strait.And the three different intrusion paths can occur in any season.In spring,with the decay of the northeast monsoon,the Kuroshio mainly intrude along the eastern Taiwan Strait by s-path I.In summer,with the enhancement of the South China Sea warm current,the Kuroshio mainly influence the southeastern Taiwan Strait by looping path(s-path II).In winter,the Kuroshio intrusion into the Taiwan Strait enhance,but most Kuroshio water is limited to the Penghu channel.The characteristics of autumn and winter are similar,and the proportion of the three paths is similar.The Kuroshio intrusion from the northern Taiwan Strait is only 2%of the total intrusion.97.8%of the intrusion from the northern Taiwan Strait occur in autumn and winter and the intrusion in winter is about three times that in autumn.There are two main paths of the intrusion from the northern Taiwan Strait.The n-path? is the main path in autumn,while n-path I in winter.In order to investigate the influence of the wind field on the Kuroshio intrusion into the Taiwan Strait,some cases are analyzed in this paper.The results show that the seasonal wind field in the Taiwan Strait affects the flow field in the channel and then influences the Kuroshio intrusion into the Taiwan strait.In addition,the typhoon can chang the direction of the Taiwan Strait northward transport temporarily and cause the Kuroshio intrusion temporarily.