Why is there net surface heating over the Antarctic Circumpolar Current?
Using a combination of atmospheric reanalysis data, climate model outputs and a simple model, key mechanisms controlling net surface heating over the Southern Ocean are identified. All data sources used suggest that, in a streamline-averaged view, net surface heating over the Antarctic Circumpolar Current (ACC) is a result of net accumulation of solar radiation rather than a result of heat gain through turbulent fluxes (the latter systematically cool the upper ocean). It is proposed that the fraction of this net radiative heat gain realized as net ACC heating is set by two factors. First, the sea surface temperature at the southern edge of the ACC. Second, the relative strength of the negative heatflux feedbacks associated with evaporation at the sea surface and advection of heat by the residual flow in the oceanic mixed layer. A large advective feedback and a weak evaporative feedback maximize net ACC heating. It is shown that the present Southern Ocean and its circumpolar current are in this heating regime.
KeywordsAntarctic Circumpolar Current Air-sea heat flux negative feedback
Discussions with Aaron Donohoe (MIT) and David Ferreira (Reading University) helped greatly in the preparation of this manuscript. David Ferreira also kindly provided the MITgcm outputs. JM acknowledges support from NSF’s ‘Frontiers in Earth System Dynamics’ program. Finally, both authors would like to thank Richard Greatbatch for countless discussions and enjoyable encounters over many years. It is a pleasure to dedicate this study to Richard’s 60th birthday.
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