Impacts of ENSO on the upper ocean in the northern South China Sea during winter

Yu-heng Tseng, National Taiwan University, Taipei, Taiwan and Yi-chun Kuo, National Taiwan University, Institute of Oceanography, Taipei, Taiwan
This study uses a high-resolution air-sea coupled model to clarify the upper ocean response to ENSO phenomenon in the northern South China Sea. In general, the basin-scale wind curl anomalies in the western North Pacific associated with El Niño events create a larger intrusion of Kuroshio into the Luzon Strait during winter than those associated with La Niña events. This steady state condition results from the balance between vorticity input by wind curl, flux of planetary vorticity and the frictional dissipation along the western boundary; known as the island rule. However, the actual Kuroshio pattern is significantly affected by mesoscale eddies and local wind forcing. Our sensitivity experiments show that the anomalous winds in the north western Pacific during El Niño favor the formation of mesoscale eddies due to the increase of the baroclinic instability in the STCC/NCE region regardless of cyclonic or anti-cyclonic eddies. Furthermore, the vorticity stretching effect contributed by the local wind stresses and wind curl anomalies during La Niña favors the formation of a cyclonic eddy off southeastern coast of Taiwan.