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Abstract:
The Atlantic Meridional Overturning Circulation (AMOC) trends on decadal time scales and larger are often masked by large interannual and seasonal variability. This variability and thus uncertainty in AMOC estimates on these scales comes from atmospheric synoptic eddies and mesoscale processes. In this study, we investigate AMOC sensitivity to synoptic and higher frequency variability in atmospheric winds. We performed the suite of sensitivity experiments with 1/12° regional configuration of MITgcm where we apply low-pass filtering to surface winds to extract variability lower than 2 days and 10 days thus capturing the impact of mesoscale variability and atmospheric cyclones respectively on the circulation in the subpolar North Atlantic. Larger magnitude of the surface winds primarily has local effects on the ocean state enhancing ocean heat loss, decreasing upper ocean temperatures, strengthening subpolar gyre, deepening the mixed layer in the Labrador Sea, and increasing the magnitude of AMOC in the lower limb. When we apply scaling factor to filtered winds so the overall time integrated energy input into every grid cell is the same as in our control experiment and the only things that changes is wind variability, we see both local and remote effects on the oceanic circulation. Larger variability of surface winds leads to weaker subpolar gyre and reduced heat loss in the Labrador Sea that later leads to the warming of surface waters in the Irminger Sea. We also further separate these effects into the ones coming from the impact of winds on buoyancy and momentum fluxes.
