The Statistical Characters Of The Mesoscale Eddies On The East Of The Luzon Strait And The Influence To The Kuroshio Current

The Luzon Strait works as an important gap connecting the Northwest Pacific and the South China Sea. The eastern region of the Luzon Strait locates at the Subtropical Countercurrent (STCC) which is the second richest in mesoscale eddies inferior to the Kuroshio Extension. The area of (120°E～140°E,17°N～25°N) is chosen to be researched as its position is close to Luzon Strait. In the paper two eddy identification methods (SSHA closed isoline method and Okubo-Weiss parameter method) are used to identify eddies and trace them. The spatial and temporal statistical characters and the kinetic characters of eddies have been achieved.The results are as follows. In the researching region 36 to 40 eddies processes appear every year with lasting time of about two months and speed of 0.6 to 0.7 longitudinal or latitudinal degrees per week. The cyclonic eddies processes with longer lasting time and faster speed is more than the anticyclonic eddies processes. The westward propagating eddies from the outer eastern ocean are the mainly source of the researching area. Eddies end their trajectories at a longitudinal band area near 122°E which proves that eddies can't go through the Luzon Strait to reach the South China. Eddies propagate mainly westward and has smaller meridianal deflection. Anticyclonic eddies is more likely to propagate equatorward and propagate more equatorward with longer lasting time. Eddies appear more frequent during the period of 1995 to 1997 and the period after 2003, meanwhile eddies propagate faster in the same period. Eddies number also changes with the different months. May is the richest month in eddies and eddies in October is the fewest in one year. Eddies distribute mainly along two latitudinal band areas comparted by the bar of 21°N to 22°N. And the eddies appearing in north beach is more frequent than the south beach.On the east of the Luzon Strait Kuroshio Current flows across whose flowing status is affected by many factors and eddies is one of the factors. This paper tries to analyze how the eddies impact on the mean current on the base of identified eddies. The analyses method is to composite the current field according to the eddies in the reference area of 124°E～126°E,20°N-22°N. We also discuss the influence of eddies' position by changing the position of the reference area.The results show that the current field of eddies is double rings structure. In detail, the cyclonic eddies with a low water level center increase its water level from inner to outer and the responding geostrophic current is anticlockwise, while the water level increase to a certain high level it turns to decrease and the responding geostrophic current changes to clockwise. For the double ring structure of eddies when cyclonic eddy approaches to the mean current it produces a northward velocity anomaly to the current firstly and then with the eddy's farther approaching to the mean flow the velocity anomaly turns to southward. The anticyclonic eddies' condition can be resemble to the cyclonic eddies. The width of the current is also be influenced by the eddies. Cyclonic eddies make the current width narrower and the anticyclonic eddies make it wider. We need to pay attention to that the eddies'impact to mean flow we discussed is linear process and the nonlinear part hasn't been discussed in this paper.