Interannual mode of sea level in the South China Sea and the roles of El Ni隳 and El Ni隳 Modoki

Abstract

ENSO-scale variation of the summer ocean circulation in the South China Sea (SCS) is investigated. The interannual mode of SSH features a north-south dipole pattern that modulates the cold jet off Vietnam. During the summers before and after the El Nin˜o, the mode has opposite signs of extrema. Strengthened circulations couple with the cold SSTAs during the El Nin˜o developing summers; weakened circulations accompany the warm SSTAs during the decaying summers. Heat advection by the basin circulation modulates the SST variation. The impact of the 1997 El Nin˜o on the SCS circulation contrasting that of 1994 and 2002 El Nin˜o Modoki is assessed. With moderate SST warming but further westward shift of the low-level convergence of the atmosphere in the equatorial Pacific, the El Nin˜o Modoki phenomenon enhanced the western North Pacific summer monsoon inside the SCS, driving stronger circulations in both the summers of 1994 and 2002.