Asymmetries between Phases of Atlantic Multi-Decadal Variability in the CMIP6 Multi Models

The asymmetry in the two opposite phases of Atlantic Multi-decadal Variability is investigated across different models using preindustrial control experiments from 46 Coupled Model Intercomparison Project 6 models. The phasal asymmetry in the relative strength of the Tropical Atlantic sea surface temperature anomalies compared to the subpolar Atlantic SST anomalies is found to vary widely across the models. One group of models exhibits a stronger tropical response during the positive phase of AMV, while another group shows a stronger tropical response during the negative phase of AMV.

In addition to the Wind-Evaporation-SST feedback, the role of the Wind-upwelling-SST feedback associated with equatorial convergence further intensifies the asymmetry in the AMV SST anomalies in the Tropical North Atlantic. While the previously reported model's preference for negative AMV was shown with limited involvement of the dynamic ocean (Beak, 2021), the newly revealed diversity in simulating AMV asymmetry calls for a more thorough investigation of the fully coupled mechanisms controlling AMV variability and underlying model biases.