The Correlation Between Southern Indian Ocean Dipole And ENSO And Its Impact On The South China Sea Summer Monsoon

Based on the Hadley Center monthly sea surface temperature data and the NCEP/NCAR daily and monthly sea level pressure data from 1950 to 2014, the characteristics of Southern Indian Ocean Dipole (SIOD) variation and its relationships with ENSO and its impact on the South China Sea summer monsoon are investigated. The results showed that(1) SIOD event is characterized by occurrence of a cold(warm) S ST anomaly in the northeast Indian Ocean and a warm(cold) SST anomaly in the southwest.SIOD are seasonal phase-locked,it develops from October to December,reaches a mature phase in following January to March, and decays from April to June. The location and intensity variation of Mascarene High and Australian High(Low)contributes to the sea surface wind anomalies,this results SST anomalies,and then becomes the SIOD.(2) The SIOD event is significantly and negatively correlated with ENSO,most positive SIOD events occur after La Nina events and most negative SIOD events occur after El Nino events. The anomalous vertical motion and anomalous tropical zonal wind, which are induced by ENSO, can affect the evolution of the eastern and western pole of SIOD, respectively. Furthermore, SIOD can also occur in isolation with a short life span, in other words,ENSO was not the cause of the SIOD,and the occurrence of the negative SIOD events is one month earlier than that of the positive SIOD events.(3 ) SIOD is the key factor affecting the date of the South China Sea Summer Monsoon(SCSSM). Corresponding to the negative(positive) phase of the SIOD, the west of Mascarene High is strong(weak) and the east is weak(strong), this help to strengthen(weaken) the Somali cross-equatorial flow and the low-level westerlies across the equatorial Indian Ocean, the West Pacific subtropical high is strong(weak)and extends eastward rapidly(slowly), thereby causing a early(late) SCSSM onset.