Decomposition of Adiabatic and Diabatic Components in the Global Meridional Overturning Circulation 

Abstract: 

The Global Meridional Overturning Circulation (GMOC) plays an important role in the redistribution of heat, freshwater, carbon, and nutrients within the global ocean, and is therefore closely linked to climate variability. Previous studies of the GMOC have largely relied on velocity data from single section to compute overturning circulation. Although these estimates are useful for describing the mean structure and overall strength of the overturning circulation, the physical mechanisms explaining GMOC’s spatiotemporal variability remains insufficiently understood. In this study, we use the ECCO V4r4 ocean state estimate for the period 1992–2017 to diagnose GMOC variability on monthly time scale by decomposing it into adiabatic and diabatic components. In the tropical regions, both the Pacific and Atlantic are controlled by adiabatic components in response to seasonal shifts of zonal winds. With increasing depth, the adiabatic component becomes more prominent at subpolar latitudes while its importance diminishes across tropical and subtropical regions in both basins. In the subpolar regions, the diabatic components show increasing importance. The diabatic and adiabatic components exhibit opposing monthly trends and jointly modulate the overturning variability. Ongoing work aims at understanding the connection of these dynamic components across latitudes and between major basins.   

Key words: GMOC; adiabatic component; diabatic component; advection;