An initial note on quasi-stationary, cold-core Lanyu eddies southeast off Taiwan Island

Abstract

Drifting buoys, satellite altimetry and satellite-derived sea surface thermal images are used to identify the existence of a large cold-core, cyclonic Kuroshio frontal eddy between Hengchun Peninsula and Lanyu, southeast off Taiwan Island around March 1996. The cold eddy accompanies an offshore meander of the Kuroshio near Lanyu, about 70 km and 100 km in horizontal zonal and meridional scales, respectively. The cold eddy is different from normal Kuroshio frontal eddies for its persisting of about 2 months near Lanyu. Supporting evidence suggests that the Kuroshio intruded into the South China Sea (SCS, hereafter) forming a loop-like structure during the persisting period of the cold eddy and that similar eddies occur occasionally in the same location. Compared with the corresponding studies in the Gulf of Mexico, it is suggested that Lanyu cold eddies are SCS analogues of Tortugas eddies found in the southern Straits of Florida. Overshooting of the meandering Kuroshio when it leaves the SCS and effects from conservation of potential vorticity are the possible mechanism of eddy genesis.