A model study of Luzon cold eddies in the northern South China Sea

A variable-grid global ocean circulation model (MITgcm) was employed to study the effects of wind and Kuroshio intrusion on the Luzon cold eddies (LCEs) in the northern South China Sea (SCS). Study findings showed that there are two cold eddies northwest of the Luzon Island. The cold eddies above 300 m and below 500 m depth are referred to as the upper and lower layer LCE, respectively, based on their different generation sites, properties and dynamic mechanisms in these layers. In this study, the upper layer LCE was mainly induced by the winter wind stress curl in the SCS and generated northwest of the Luzon Island in late November, but it may have been weakened by the Kuroshio intrusion. It moved northwestward and decayed at about (115°E, 20°N) in late June. The center of the upper layer LCE tilted westward with increasing depth until March. The vorticity intensity of the upper layer LCE peaked in December to January and generally decreased with depth. The contributions of both wind stress curl and Kuroshio intrusion to the generation of the lower layer LCE were roughly equal. The lower layer LCE originated from a cold eddy, which moved westward from the Luzon Strait in August through October and then intensified by wind stress curl. Subsequently, it moved westward with a slight southward migration and finally decayed near the Xisha Islands in April to May. Its amplitude and radius reached a maximum around December, while the vorticity intensity peaked in January to February.