Optimal estimation of absolute geostrophic velocity field in vicinity of the Luzon Strait using variational data assimilation technique

A P-vector method is optimized using the variational data assimilation technique(VDAT).The absolute geostrophic velocity fields in the vicinity of the Luzon Strait (LS) are calculated,the spatial structures and seasonal variations of the absolute geostrophic velocity field are investigated.Our results show that the Kuroshio enters the South China Sea (SCS) in the south and middle of the Luzon Strait and flows out in the north,so the Kuroshio makes a slight clockwise curve in the Luzon Strait,and the curve is strong in winter and weak in summer.During the winter,a westward current appears in the surface,and locates at the west of the Luzon Strait.It is the north part of a cyclonic gyre which exits in the northeast of the SCS; an anticyclonic gyre occurs on the intermediate level,and it exits in the northeast of the SCS,and an eastward current exits in the southeast of the anti-cyclonic gyre.