AMOC Dynamics

Abstract

This study examines the applicability of the Gnanadesikan four-box model of the Atlantic Meridional Overturning Circulation to a global earth system model. The Community Earth System Model 2 (CESM2) is used to quantify the extent to which pycnocline depth and AMOC strength as predicted by the four-box model from regional densities and Southern Ocean fluxes match CESM2 values. The dynamics of a reduced meridional density difference driving a deepening pycnocline and weakening AMOC are qualitatively matched between the 4-box model and CESM2. We will quantify the fraction of variability in the CESM2 Large Ensemble of historical and SSP3-7.0 runs that is explained by the 4-box model; initial results suggest about two-thirds of the variability in AMOC is explained and over 90% of the variability in the pycnocline depth. This analysis may be repeated for any CMIP6 model, and a comparison of SSP5-8.5 across a handful of models is included as a demonstration.