Two Branches of the Eastward Countercurrent in the Subtropical Region of the North Pacific
北太平洋副热带海区的两支东向逆流

The upper\|layer eastward countercurrents in the subtropical region of the North Pacific is presented in the Simple Ocean Data Assimilation (SODA) data set. The countercurrents comprise two branches in climatology, i e., the east branch and the west branch. The east branch locates at the middle Pacific with its east limit to the west of Hawaiian Islands and a somewhat lower latitude than the other. The velocity of the east branch has an annual variation with its maximum occurs in the summer while the minimum in the spring. The Ekman pumping deduced by the curl of wind stress accounts mainly for the formation of the east branch. The west branch is seen over the western Pacific and has a larger intensity in both seasons of the spring and the summer. The cause of the formation, as well as the annual variation, of the west branch is explained by the convergence of subtropical mode water.