Presenter: Josh Studholme (Yale University)

Description:
The causal origin of Atlantic Multidecadal Variability (AMV), and specifically its connection to the Atlantic meridional Overturning Circulation (AMOC), remains intensely debated. Many studies have found that in various coupled climate GCMs intrinsic AMV, i.e., variability not forced by anthropogenic or volcanic activity, is largely dominated by oscillations in oceanic overturning. However, it has also been shown that AMV may be produced without active ocean dynamics in slab-ocean models. Moreover, simulated AMV/AMOC linkages vary widely across climate models - maximum temporal correlations between the two phenomena vary in the CMIP6 pre-industrial control runs from 0.3 to 0.8. Here we use coupled climate models, idealised model sensitivity analysis, first-principle physics and observations, to quantify, explain, and constrain the wide diversity in simulated linkages between AMOC and AMV. We detail the physical mechanism governing the jet stream’s influence over the relative strength of deep convection in the Labrador/Irminger Seas versus the Nordic Seas. We then show how these processes influence AMOC strength and structure in such a way as to regulate AMOC links to AMV. Using atmospheric reanalysis, we further show that average climate models may underestimate the AMOC-AMV linkage and thereby underestimate seasonal-to-decadal climate predictability. Intriguingly, we also find that the mechanisms that control AMOC-AMV linkage also regulate high latitude northern climate change – influencing the degree of Artic Amplification by nearly 5ºC and modulating the strength of the North Atlantic “warming hole”.