Impact of the Interdecadal Pacific Oscillation on tropical Indian Ocean sea surface height: An assessment from CMIP6 models

This study examined the sea level (SL) changes on the interdecadal timescale in the tropical Indian Ocean (TIO) in response to the Interdecadal Pacific Oscillation (IPO) in 20 Coupled Model Intercomparison Project Phase 6 (CMIP6) models. The analysis suggests that the interdecadal sea level pattern variation in the Thermocline Ridge of the Indian Ocean (TRIO) area coincides with the IPO phases and is mainly caused by fluctuations of surface forcing over the TIO. Changes in tropical wind stress curl (WSC) mainly induce the SL variability on the interdecadal timescale associated with IPO in the TRIO region in both observations and models. The stochastic wind forcing and its interaction with the ocean's internal variability produce significant interdecadal SL fluctuation in the southeast Indian Ocean. We evaluated the ability of 20 CMIP6 models to capture interdecadal variations in sea level teleconnections. We found that about 75% of models reproduce decadal fluctuations related to IPO pretty well. The interdecadal variations of the SL in the western TIO emerge primarily in response to westward propagating downwelling Rossby waves induced by the WSC in the central-south TIO in MMM, and models as in observations. Pacific IPO-related anomalies primarily spread through the oceanic pathways of the Maritime Continent in the eastern Indian Ocean. Further, the IPO induces changes in the western Indian Ocean WSC through atmospheric pathways, which in turn causes Rossby waves to move westward, affecting the southwest Indian SL. Almost all the models and MMM show interdecadal SL variations in TIO associated with IPO. This study is beneficial as interdecadal prediction research on SL has a significant societal need.