Teleconnection and the Antarctic response to the Indian Ocean Dipole in CMIP5 and CMIP6 models

Tropical-Antarctic teleconnections are known to have large impacts on Antarctic climate variability at multiple timescales. Anomalous tropical convection triggers upper-level quasistationary Rossby waves, which propagate to high southern latitudes and impact the local environment. Here the teleconnection between the Indian Ocean Dipole (IOD) and Antarctica was examined using daily gridded reanalysis data and the Linear Response Theory Method (LRTM) during September–November of 1980–2015. The individual contribution of the IOD over the Antarctic climate is challenging to quantify as positive IOD events often co-occur with El Nino events. However, using the LRTM, the extratropical response due to a positive IOD was successfully extracted from the combined signal in the composite map of anomalous 250-hPa geopotential height. Applying the method to a set of models from phase 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6), significant differences were observed in the extratropical response to the IOD among the models due to bias in Rossby waveguide and IOD precipitation pattern. The LRTM was then applied to evaluate the extratropical response of the 850-hPa temperature, wind anomalies, and sea ice concentration anomalies in observation data, and models that adequately represented both the IOD precipitation and the extratropical waveguide. The IOD-induced cold southerly flow over the west of the Ross Sea, the Weddell Sea, and the Antarctic Peninsula, causing cold surface temperature anomalies and the increase of sea ice, and warm northerly flow over the east of the Ross Sea and the Amundsen Sea, causing warm surface temperature anomalies and the decrease of sea ice. We recommend the LRTM as a complementary method to standard analysis of climate variability from observations and global climate models.