Origin of underestimated Indian Ocean Dipole teleconnections to Australia in CMIP6 models

Abstract

The Indian Ocean Dipole (IOD) significantly modulates the Australian climate via extratropical Rossby wave teleconnections. However, current Coupled Model Intercomparison Project Phase 6 models generally overestimate the IOD amplitude while underestimating its remote impacts on Australian precipitation and surface air temperature. This historical underestimation stems from a deficient atmospheric response over the western tropical Indian Ocean. Due to the overly strong and westward-extending eastern pole of the IOD, models fail to generate sufficient diabatic heating and upper-level divergence in the west. The western basin is the key upstream region capable of bypassing the reflective waveguide barrier of the Southern Hemisphere subtropical jet. This discrepancy impacts the Rossby wave source to build the equivalent-barotropic dynamic bridge to Australia. Because this historical teleconnection pathway is flawed, future projections are highly uncertain. While models project intensified IOD impacts under high-emission scenarios, this amplification may be related to background jet changes rather than a robust IOD response. Correcting spatial biases in tropical diabatic heating is thus essential for reliable regional climate predictions.