PNNL

Abstract

The relative roles of the ocean and the atmosphere in driving the Atlantic Multi-decadal Oscillation (AMO) are investigated by isolating the AMO components forced by anomalous surface heat fluxes and ocean dynamics in a fully- and partially-coupled experiments. The impact of the ocean-dynamics-forced SST on air-sea interaction is disabled in the partially-coupled experiment in order to isolate the atmosphere-forced variability. In the partially-coupled experiment, the ocean-forced AMO component exhibits a strong multi-decadal variability (25- to 50-yr periods), while the atmosphere-forced component has weak multi-decadal variability. This ocean-forced variability is imprinted on the fully-coupled surface heat fluxes, which however, damp the ocean-forced SST variability inducing them, so that the fully-coupled AMO multi-decadal power is only slightly stronger than that forced by the atmosphere alone. Our results suggest that the multi-decadal variability of the AMO is largely driven by ocean dynamics, but its power is also determined by the strength air-sea coupling.