ENSO teleconnections with the NAE sector during December in CMIP5/CMIP6 models: impacts of the atmospheric mean state

This study investigates how the atmospheric mean state influences the El Niño-Southern Oscillation (ENSO) teleconnections with the North Atlantic-European (NAE) region, using ERA5 and CMIP5/CMIP6 models. By isolating the contributions of heating anomalies in the Niño 3.4 and Tropical Western-Eastern Indian Ocean (TWEIO) regions, we find that in November, the Niño 3.4 teleconnection dominates, projecting onto the positive phase of the North Atlantic Oscillation (NAO). In December, the TWEIO teleconnection prevails, reinforcing the positive NAO via a zonal wavenumber-3 Rossby wave train originating from SouthEast Asia (SEA). Models that fail to simulate the December ENSO teleconnection with the NAE exhibit a weak Rossby wave source in SEA and overly strong subtropical Pacific and Atlantic jet streams, which trap Rossby waves at lower latitudes, affecting the remote atmospheric response over the NAE. This waveguide bias is likely driven by a cold bias in the northern Pacific and Atlantic, a common mean-state error in climate models.