Roles of atmospheric variabilities in the formation of the Indian Ocean Dipole

Roles of atmospheric variabilities in the formation of Indian Ocean Dipole (IOD) were investigated using an ocean general circulation model and different atmospheric forcing datasets. Simulated IODs indicated that IOD amplitude decreased without intraseasonal variability and the sea surface temperature anomaly (SSTA) peaks moved northward, resulting in unrealistic SSTA patterns. Analysis on the tendencies contributing to forming the SSTA of IODs revealed that the oceanic vertical processes were mainly influenced by seasonal variability, which was related to El Nino (La Nina) through anticyclonic (cyclonic) surface wind circulation and equatorial Kelvin waves in the Indian Ocean. Madden-Julian oscillations (MJOs) were found to have large impacts on the change in latent heat flux and surface wind anomaly that controlled the SSTA. In the wake region of MJOs, surface easterly (westerly) wind anomalies were magnified due to the suppressed (enhanced) convection phase of the MJO, whereas the effect of the opposite phase was weakened by the preceding anticyclonic (cyclonic) sea level pressure for positive IODs (negative IODs). Further, the MJO modulated meridional gradient of sea level pressure anomaly, and the resulting effect changed the locations of SSTAs.