Mechanism of weakening of west Luzon eddy during La Niña years

Multi-satellite sea level anomalies from January 1993 to December 2004 are used to investigate the variability of sea surface features in the South China Sea (SCS). Applying empirical orthogonal function (EOF) analysis, the dominant spatial features and corresponding temporal variability are revealed. The most remarkable characteristic of variability on an interannual time scale is the abnormal weakening of meso-scale eddy off west Luzon (west Luzon eddy, WLE) during 1998-2001. The possible mechanism inducing the weakening is found to be associated with a large-scale forcing over the Pacific intruding into the northern SCS along the northern coast of Luzon. Moreover, the tight correlation between the Niño3.4 sea surface temperature index and the interannual variability of large-scale forcing indicates that La Niña events may modulate the west Pacific water entering the northern SCS which contributes to the weakening of the WLE eventually.