The Characteristics And Evolution Of Southern Indian Ocean Dipole And Its Correlation Relationships With ENSO

Southern Indian Ocean Dipole is significant dipolelike sea sueface temperature (SST) pattern in the Southern Indian Ocean. It is robust in the interannual and interdecadal time scale, and distinguished difference from the SST dipole in the tropical Indian Ocean. However, most previous researches focused on dipole in the tropical region of Indian Ocean, seldom work paid attention to the Southern region. Using monthly OISST、ERSST and NCEP2reanalysis, the characteristics and evolution of SIOD, and its interdecadal variations and correlation with ENSO are investigated in this study. The mainly results are as follows:(1)The variance analysis of the Indian Ocean sea surface temperature (SST) indicates that a strong dipole oscillation occurs in the Southern Indian Ocean, so called Southern Indian Ocean Dipole(SIOD). Usually, SIOD develops in November, peaks in February and decays in April-June of the next year. Wind, latent heat flux and shortwave radiation flux play an important role in the formation of SIOD. Besides, the change of the mixed layer depth contributes to the formation of SIOD. Further study indicated that the formation of SIOD is associated with the Antarctic Circumpolar process. Moreover, SIOD as well as the corresponding sea level pressure,500hPa geopotential height field and850hPa wind field over Southern Indian Ocean can be regarded as part of the southern hemisphere circumpolar modes of coupled ocean-atmosphere.(2)In recent three decades, SIOD are phase-locked to the austral summer season, preceding the El Nino signal by9toll months. Furthermore, El Nino events usually occur after positive SIOD (PSIOD), while La Nina events occur after negative SIOD (NSIOD).When PSIOD events occur in January to March and at the same time La Nina events occur in the previous winter, the two poles of SIOD will be exceptionally northerly. Particularly the location of the cold center will deflect obviously to north-west than other years, the southeast wind anomalies stronger, and westerly anomalies will propagate eastward in the equatorial Indian Ocean, Vice versa the situation of NSIOD occur in January to March and at the same time El Nino events occur in the previous winter. ENSO events will exert a certain impact on the strength and location of SIOD.(3)SIOD exhibits interdecadal variations in the longer time-scale. The intensities of SIOD are strongest in the1960s and1970s, but it’s relationship with ENSO is enhanced after mid1970s, the inter-decadal abrupt climate change. This enhance may be related to the Pacific Decadal Oscillation (PDO) and global warming. The east pole and Nino3.4NDJ index presents the inverse correlation. Furthermore, the relationship between SIOD and IOD also increase correspondingly because of the relationship of ENSO and IOD enhanced after the mid-1970s. It is worth noting that the east pole of SIOD splits into two centers after the end of1980s, resulting in three poles distribution of SIOD.