May 28th, 2019
Key Findings
- Observed AMV exhibits strong coherent variability that is unique to the Atlantic after removal of the signal regressed on global mean SST.
- The CMIP5 multi-model mean forced AMV, after removal of the signal regressed on global mean SST, shows little resemblance to observed AMV.
- This study includes a novel multivariate AMV analysis and suggests that the observed AMV is not dominated by external forcing.
Xiaoqin Yan, Rong Zhang, and Thomas R. Knutson. Geophysical Research Letters. DOI: 10.1029/2019GL082787
The Atlantic Multidecadal Variability (AMV) has profound climate impacts. Improvement of our understanding of the AMV mechanisms is crucial for successful future prediction of AMV and associated climate impacts, with enormous social and economic implications.
Observed AMV is a multivariate phenomenon and has climate impacts at global and regional scales. Understanding its driving mechanism and identifying the discrepancies between observed and simulated, externally forced AMV is important to resolve the ongoing debate about AMV mechanisms. From a multivariate perspective, this study shows that the simulated externally forced AMV in coupled climate model simulations disagrees strongly with that observed, and emphasizes the need to remove the signal associated with global mean sea surface temperature to accurately derive AMV. The results suggest that the observed AMV is not dominated by external forcing, but is unique to the Atlantic and is linked to multidecadal variations of the Atlantic Meridional Overturning Circulation.
The authors used both observations and simulations from multiple models of the Coupled Model Intercomparison Project Phase 5 (CMIP5), to define a multivariate AMV index (MAI) to understand the mechanism of the observed AMV and resolve the ongoing debate about AMV.
