The Southern Ocean air-sea buoyancy flux obtained from the Southern Ocean State Estimate

The Southern ocean plays a fundamental role in the global overturning circulation and in setting global climate, but detailed understanding of air-sea buoyancy fluxes in the SO is limited due to the sparseness of both conventional and remotely sensed atmospheric and oceanic observations. In the last several years the number of oceanic observations has greatly increased, which raises the question: can oceanic observations provide a valuable constraint on the atmospheric state?

We have carried out a comparison of the Southern Ocean air-sea heat and freshwater flux estimates for years 2005-2007 from the eddy-permitting "Southern Ocean State Estimate" (SOSE) by Mazloff et al. (2010) and five other widely used air-sea flux estimates. SOSE is a general ocean circulation model constrained to a large set of oceanic observations. Our goal is to assess the accuracy of SOSE fluxes, to identify the main weaknesses of the SOSE solution, and to determine how the SOSE solution could be improved. The differences between both heat and freshwater flux estimates by the six products considered here are large reaching the largest values over the strong ocean currents where mesoscale activity is heightened (e.g. the Antarctic Circumpolar Current and western boundary currents), emphasizing the importance of a two-way atmosphere-ocean feedback and resolving mesoscale oceanic features. The large differences between both heat and freshwater flux estimates by the six products considered here clearly indicate that significant uncertainties remain, and highlight the need for high-quality in-situ observations. Our results suggest that these observations need not strictly be of atmospheric variables, as ocean observations provide a valuable constraint on the atmospheric state.