Impacts of the atmospheric mean state on austral early-winter Indian Ocean teleconnections with Chile in CMIP5/CMIP6 models

This study investigates the impacts of atmospheric mean state biases on the Indian Ocean teleconnection with Chile, using ERA5 reanalysis and CMIP5/CMIP6 models. During austral early-winter (May-June), Indian Ocean heating anomalies trigger a dipole of increased (reduced) precipitation over central (southern) Chile. The dipole is driven by cyclonic circulation anomalies induced by a zonal wavenumber-3 Rossby wave train originating from South Australia. Models that fail to simulate this rainfall dipole consistently exhibit an equatorward shift of the Southern Hemispheric eddy-driven jet stream. The associated waveguide weakening displaces the refraction location of zonal wavenumber-3 waves westward, thus shifting anticyclonic anomalies from the Amundsen Sea toward Chile. Consequently, the dry signal associated with the Indian Ocean teleconnection moves from southern to central Chile. This waveguide bias likely stems from a reduced meridional gradient of surface temperature, linked to an underestimated Antarctic Sea ice cover. For this reason, accurately simulating Antarctic Sea ice cover is crucial for a better representation of the Indian Ocean teleconnection to Chilean rainfall.