Hemispheric energy balance from an ocean perspective

Although the Earth's energy balance has been studied for many decades, a number of challenges still remain in quantifying it globally and in understanding its behavior regionally. The recent advances in satellite-based radiation products allow to estimate the top-of-atmosphere (TOA) energy budget with unprecedented accuracy. In contrast, no equivalent data record exists for the energy balance at the surface with associated uncertainties being much larger than the small imbalance of 0.6 Wm-2 inferred from changes in ocean heat content. Recent studies combine the total and atmospheric heat budgets derived from satellite-based TOA irradiances and atmospheric reanalysis to infer the hemispheric surface heat budget as their residual. Here, we propose an approach that takes the perspective of the ocean, deriving the multi-annual surface net heat flux as the residual of the hemispheric ocean heat storage (OHS) and cross-equatorial ocean heat transport (OHT). The latter is taken from ocean model solutions (i.e. ECCOv4), while the OHS is derived from in-situ temperature profiles covering the ARGO period 2005-2015. Notable features of the hemispheric energy balance portrayed here are the dominance of the Southern hemispheric oceans in taking up heat (0.9 Wm-2) and the slight inter-hemispheric energy imbalance that leads to a net cross-equatorial heat transport from the Southern to the Northern hemisphere. This is achieved by the oceans transporting about 0.45 PW northward across the equator, accompanied by a southward transport of heat by the atmosphere (0.2-0.3 PW). The hemispheric turbulent heat fluxes, calculated as the residual of the net balance at the surface and satellite-derived surface radiative flux (CERES EBAF), differ by about 3 Wm-2, which is largely in line with the hemispheric contrast in precipitation according to GPCP data.