GFI/BCCR Seminar: Reconstructing recent Atlantic overturning from surface forcing

Helen Johnson (Department of Earth Sciences, University of Oxford, UK):

Reconstructing recent Atlantic overturning from surface forcing

Abstract
The Atlantic Meridional Overturning Circulation (AMOC) transports a substantial amount of heat poleward in the North Atlantic and is projected to weaken over the next century in response to greenhouse gas emissions, with implications for the North Atlantic storm track, European climate, hurricane statistics and other climate metrics. The AMOC is believed to be a key driver of multidecadal variations in North Atlantic sea surface temperatures and a potential source of regional climate predicability.

The strength of the AMOC at 26N has been continuously monitored since 2004 and exhibits large variability on all time scales. Here we investigate how much of the recent AMOC variability can be reconstructed by projecting observed surface forcing onto model-based estimates of AMOC sensitivity to surface wind, thermal and freshwater forcing over the preceding 15 years. We find that local, contemporaneous, wind forcing dominates the AMOC variability on short time scales, whereas subpolar heat fluxes dominate on interannual- to-decadal time scales. The reconstructed AMOC is able to reproduce most of the interannual variability observed by the RAPID-MOCHA array at 26N, but not the decadal trend which is driven by subpolar heat fluxes over at least the past two decades.