The Kuroshio intrusion into the SCS through the Luzon Strait is an important process. Because of the intrusion, an eddy is located northwest of Luzon Island. Many papers reported the eddy. However, the eddy was claimed to be either cyclonic or anticyclonic. Based on the P-Vector inverse method, the circulation field is calculated from the GDEM data, and the eddy is identified as cyclonic in the upper layer and as anticyclonic in the lower layer. The results suggest that the anticyclonic eddy originates from Kuroshio intrusion, and the cyclonic eddy is due to the South China Sea Warm Current.
The South China Sea (SCS) is a large marginal sea located between the Asian landmass to the north and west, the Philippine Islands to the east, Borneo to the southeast, and Indonesia to the south. The SCS is a partly enclosed ocean basin with connections to the surrounding waters through straits. In the northeast, it joins the Pacific Ocean via the wide and deep Luzon Strait between Taiwan Island and Luzon Island. The Luzon Strait with >3000m maximum depth is the principal passage for water exchange between the SCS and the Western Pacific (Fig. 1). The Kuroshio, the western boundary current of the North Pacific Ocean, flows northward east of Luzon and Taiwan islands. While it goes northward, the Kuroshio will pass through the Luzon Strait and intrude into the SCS. Because of the Kuroshio intrusion, an eddy is located northwest of Luzon Island. Many papers reported the eddy. However, the eddy was claimed to be either cold-core cyclonic or warm-core anti-cyclonic. Nitani (1970) used limited data to identify this eddy as cold-core cyclonic, occurring in the summer. Xu, Qiu and Chen (l982) used historical (l92l--l970) hydrographic data to identify this eddy as cold-core cyclonic, occurringin the winter.
