Mechanisms controlling net air-sea heatflux over the Southern Ocean

The role of large-scale atmospheric eddies and the mean meridional circulation (the Ferrell cell) in explaining the observed net heating of the ocean in the latitude band of the Antarctic Circumpolar Current (ACC) is examined in the NCEP-NCAR reanalyses. Emphasis is placed on processes limiting evaporative cooling rather than on on those promoting radiative heat gain. It is found that the moistening and drying of low levels induced by eddy and Ferrell cell moisture transports is small (' 0.1 − 0.2Sv, 1Sv = 109kgs−1) in comparison of the moistening caused by surface evaporation (' 1.5Sv). As a result, it is suggested that evaporative cooling over the ACC is controlled by vertical moisture exchange between the free-troposphere and the boundary layer rather than by lateral moisture fluxes. From the perspective of large scaIe ocean atmosphere interactions, it is argued that a warm and moist midlatitude jet and the dynamical oceanic response to the associated surface windstress (inducing upwelling of cold water on the poleward flank of the ACC and its subsequent equatorward advection) are the two key ingredients required to explained net ocean heat gain over the ACC.