Atlantic Multidecadal Variability driven by the western current warming–eastern low cloud reduction mechanism

The Atlantic Multidecadal Variability (AMV) is a prominent mode of low-frequency climate variability, characterized by basin-scale sea surface temperature (SST) variations in the North Atlantic and strong global impacts. AMV can be forced externally by surface radiative fluxes or internally generated. The latter generation mechanism is commonly attributed to variations in the Atlantic Meridional Overturning Circulation (AMOC). Here we show that a robust AMV can arise and be sustained by large-scale atmosphere–ocean interactions, even in the absence of a dominant role for AMOC variations, in a fully coupled model—the Department of Energy’s Energy Exascale Earth System Model version 2 (E3SMv2). The simulated AMV is driven primarily by surface shortwave and turbulent heat fluxes across the North Atlantic. Essentially, an initial warming over the Gulf Stream region strengthens and spreads by reducing low cloud cover and enhancing surface shortwave radiation. This mechanism is enabled by the relatively narrow width of the North Atlantic, compared to the North Pacific. Our results broaden the conceptual understanding of AMV physics and underscore the importance of atmosphere–ocean interactions in sustaining it.