Impacts of Different Types of ENSO Events on Thermocline Variability in the Southern Tropical Indian Ocean

Abstract

Remarkable interannual variability in the thermocline depth in the southern tropical Indian Ocean (STIO) is analyzed using reanalysis data during 1980–2017. Previous studies have shown that the El Niño-Southern Oscillation (ENSO) has a significant relationship with thermocline depth anomalies in this region. We find that both the eastern-Pacific (EP) and central-Pacific (CP) ENSO have important impacts on the STIO thermocline variation. The positive and negative phases of thermocline anomalies in the STIO are induced by asymmetric forcings from the two phases of ENSO. EP-El Niño and CP-La Niña events tend to induce larger thermocline depth anomalies in the STIO. Equatorial westerly and STIO anticyclonic winds during EP-El Niño events can induce downwelling Rossby waves that extend far toward the western Indian Ocean, which dominates the westward propagation of thermocline anomalies, while upwelling Rossby waves during CP-La Niña events cannot extend that far west.