CMIP6 Models Underestimate ENSO Teleconnections in the Southern Hemisphere

This study evaluates the capability of the Coupled Model Intercomparison Project Phase 6 (CMIP6) models to simulate El Ni & ntilde;o-Southern Oscillation teleconnections in the Southern Hemisphere during austral summer. The wave trains from the tropical Pacific to the Amundsen Sea are underestimated and too far westward in CMIP6 simulations. However, Atmospheric Model Intercomparison Project Phase 6 (AMIP6) experiments well capture the observed location and amplitude of the teleconnection. El Ni & ntilde;o and La Ni & ntilde;a-related tropical precipitation anomalies are underestimated in CMIP6 and have their maximum amplitude too far westward, while the precipitation responses in AMIP6 simulations are similar to those observed. The weaker precipitation response in CMIP6 likely arises from a cold bias in climatological-mean SST, which reduces the sensitivity of precipitation to SST anomalies. Increased resolution in coupled experiments eradicates the westward bias in the El Ni & ntilde;o and La Ni & ntilde;a-related circulation anomalies over the Amundsen Sea, but not their insufficient amplitude. Abnormally warm and cold sea surface temperatures (SST) in the tropical Pacific during El Ni & ntilde;o and La Ni & ntilde;a events, respectively, generate atmospheric circulation anomalies that propagate across the Southern Hemisphere toward the Amundsen Sea, where they influence west Antarctic climate. In this study, we evaluate how well state-of-the-art climate models simulate these El Ni & ntilde;o and La Ni & ntilde;a-related teleconnections. We find that free-running models simulate teleconnections that are too weak and too far westward. When models are provided with realistic SST however, they well simulate the teleconnection location and amplitude. The errors in free-running models likely occur because the models are too cold in the tropical Pacific, and this reduces the sensitivity of simulated rainfall to SST anomalies; and the SST anomalies are too far westward. Increased ocean resolution eradicates the error in the location of the El Ni & ntilde;o and La Ni & ntilde;a teleconnections but does not substantially improve their strength. CMIP6 models underestimate the intensity of observed ENSO teleconnection to the Amundsen Sea and simulate a westward bias in the wave train Experiments prescribed with historical global SST and sea ice, closely match the location and strength of observed ENSO-related wave train Increased ocean resolution eliminates the westward bias in the wave train responses to ENSO, but not their insufficient amplitudes