Interannual variability of the thermocline depth in the south-central Indian Ocean: Respective influences of IOD and ENSO

The respective influences of the Indian Ocean dipole (IOD) and El Nino-Southern Oscillation (ENSO) on the thermocline depth (represented by the 20 degrees C isotherm depth, D20) variability in the south-central Indian Ocean (SCIO) are investigated for the period of 1960-2020. The results show that pronounced interannual variations in D20 mainly occur in the SCIO and display a close relationship with the two tropical climate modes, with positive (negative) phase being associated with SCIO D20 deepening (shoaling). The D20 anomalies (D20A) induced by IOD and ENSO events have the same intensities but present different spatial-temporal features, as demonstrated by partial regression analysis. The IOD-related D20A occurs during the mature phase of the event and behaves as a local response to anomalous wind stress curl induced by IOD, while the ENSO signature, dominated by the westward-propagating oceanic Rossby waves, lasts much longer and extends further west.