Decadal Variation of the Kuroshio Intrusion Into the South China Sea During 1992-2016

Decadal variation of the Kuroshio intrusion into the South China Sea (KIS) during 1992-2016 is investigated using high-resolution Hybrid Coordinate Ocean Model reanalysis data. The results indicate that both the yearly occurrence frequency of the Kuroshio intrusion and Luzon Strait transport show significant decadal variations and were generally high in approximately 1993, 2003-2004, and 2015-2016 and low in 1998-1999 and 2009-2010. The KIS is closely connected to the decadal oscillation of the meridional sea surface height anomaly (SSHA) gradient west of the Luzon Strait (LS). Further analyses reveal that large-scale wind forcing in the western tropical Pacific Ocean is a major factor regulating decadal variation of the KIS, while local wind forcing has little impact. Cyclonic wind stress curl anomalies (WSCAs) over the western tropical Pacific Ocean induce negative SSHAs that propagate westward to the eastern coast of the Philippines via upwelling Rossby waves, weakening the Kuroshio transport and consequently enhancing the KIS. In addition, signals of negative SSHAs can propagate clockwise along the Philippines as coastal Kelvin waves and hence strengthen the northward SSHA gradient west of the LS, eventually leading to a stronger KIS. The situation is reversed when anticyclonic WSCAs prevail in the western tropical Pacific Ocean. The Philippines-Taiwan Oscillation is linked to decadal WSCAs over the western tropical Pacific Ocean and hence regulates the decadal KIS.