A clearer view of Southern Ocean air–sea interaction using surface heat flux asymmetry

Abstract

Progress in understanding Southern Ocean heat exchange and wind forcing is discussed and new results presented. These include a metric of the zonal asymmetry between surface ocean heat gain in the Atlantic/Indian sector and heat loss in the Pacific sector. The asymmetry arises from an intersector variation in the humidity gradient between the sea surface and near-surface atmosphere. This gradient increases by 60% in the Pacific sector enabling a 20 Wm −2 stronger latent heat loss compared with the Atlantic/Indian sector. The new metric is used for intercomparison of atmospheric reanalyses and CMIP6 climate simulations. CMIP6 has weaker Atlantic/Indian sector heat gain compared with the reanalyses primarily due to Indian Ocean sector differences. The potential for surface flux buoys to provide an observation-based counterpart to the asymmetry metric is explored. Over the past decade, flux buoys have been deployed at two sites (south of Tasmania and upstream of Drake Passage). The data record provided by these moorings is assessed and an argument developed for a third buoy to sample the Atlantic/Indian sector of the asymmetry metric. To close, we assess evidence that the main westerly wind belt has strengthened and moved southward in recent decades using the ERA5 reanalysis. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

Cloud Properties and Boundary Layer Stability Above Southern Ocean Sea Ice and Coastal Antarctica

“…We examined ERA5 surface sensible and latent heat fluxes around the ship as a function of both latitude (Figure S7 in Supporting Information S1) and surface type (Figure S8 in Supporting Information S1). ERA5 yields heat flux results in line with those produced by the foremost ocean reanalysis for the SO and uses a resolution of 0.25°× 0.25°, which is high relative to the global reanalysis standard (Josey et al, 2023). Average surface heat fluxes during the MARCUS campaign were generally negative, denoting a consistent loss of heat from the ocean to the atmosphere through both direct heat exchange (sensible) and phase changes such as condensation and evaporation (latent).…”

Southern Ocean deep mixing band emerges from a competition between winter buoyancy loss and upper stratification strength

“…This is due to large radiative heat fluxes compared to small sensible heat fluxes (Czaja and Marshall, 2015). Thus, heat fluxes are not zonally constant in the ACC (Song, 2020;Josey et al, 2023). Overall, in both the Indian and Pacific sectors of the SO, the DMB is surrounded by annual heat gain in the north and south.…”

Southern ocean carbon and heat impact on climate

“…The Southern Ocean provides a preferential pathway for ventilation, with more than 60% of the world’s ocean waters having their last contact with the atmosphere in this region [ 23 ]. Carbon and heat ventilation involves two main steps: (i) fluxes through the ocean surface [ 24 ] and (ii) transfer from the surface boundary layer to the deeper ocean, where such tracers are isolated from the atmosphere. The transfer from the surface boundary layer of the Southern Ocean to deeper waters can take place either in the open seas through mixing and subduction [ 25 , 26 ], or along Antarctic margins through the formation and export of dense bottom waters [ 27 ].…”