Strengthened Relationship Between Tropical Indian Ocean Dipole and Subtropical Indian Ocean Dipole After the Late 2000s

This study identifies a strengthened relationship between the subtropical Indian Ocean dipole (SIOD) during January-February-March (JFM) and the following autumn Indian Ocean dipole (IOD) after the late 2000s. Following the positive SIOD, the northwesterly wind anomalies help to maintain positive sea surface temperature (SST) anomalies in the southwestern tropical Indian Ocean by wind-evaporation-SST (WES) feedback during June-July-August (JJA). The anomalous northwesterly winds and the sustained positive SST anomalies promote the development of the zonal wavenumber-3 pattern (ZW3P) and induce low-level convergence in the mid-latitude central southern Indian Ocean, leading to the anticyclone circulation over the northern Indian Ocean by the local Hadley circulation during JJA. The accompanying central equatorial easterly wind anomalies appear in JJA, which is the key to trigger a positive IOD event through Bjerknes feedback. This mechanism for the enhanced SIOD-IOD relationship is independent from the El Nino-Southern Oscillation (ENSO).

Automated summary

This study reveals a strengthened relationship between the subtropical Indian Ocean dipole (SIOD) during January-February-March and the following autumn Indian Ocean dipole (IOD) after the late 2000s. The positive SIOD leads to northwesterly wind anomalies during June-July-August, maintaining positive sea surface temperature anomalies in the southwestern tropical Indian Ocean. These anomalies promote the development of the zonal wavenumber-3 pattern (ZW3P) and induce low-level convergence in the mid-latitude central southern Indian Ocean.