Using zonal surface heat flux asymmetry to reveal new features of Southern Ocean air-sea interaction

New results on Southern Ocean heat exchange and wind forcing are presented with a focus on 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 to the Atlantic/Indian sector. A new zonal asymmetry metric is used for intercomparison of atmospheric reanalyses and CMIP6 climate simulations. CMIP6 has weaker Atlantic/Indian sector heat gain compared to 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. In addition, we assess evidence that the main westerly wind belt has strengthened and moved southward in recent decades using the ERA5 reanalysis. We find only marginal evidence of a southward broadening of the belt in the Atlantic /Indian sector and northward broadening in the Pacific sector and that the latitude of maximum wind speed remains essentially unchanged.