The radiation and energy budget over Antarctic Sea Ice: Insights from the SURFEIT Project

The Antarctic Peninsula has undergone exceptional warming, triggering major changes in sea ice extent in the Bellingshausen and Weddell Seas and modifying the regional radiation and atmospheric energy balance. Understanding and representing air-sea-ice interaction processes remains a fundamental requirement for reliably projecting future climate change in the ice-covered Southern Ocean and its implications beyond the polar regions. As part of the SURFEIT (Surface Fluxes in Antarctica) project, airborne observations of turbulent fluxes, long and shortwave radiation, and surface characteristics are analysed to assess the role of sea ice, leads, and coastal polynyas in shaping the Antarctic atmospheric boundary layer and its radiation and energy balance. The analysis shows that variations in sea ice parameters, including albedo, temperature, and ice concentration, significantly influence both the surface energy budget and atmospheric boundary layer development. In austral summer conditions, radiative terms dominate the surface energy balance in sea-ice-covered regions, with turbulent sensible and latent heat fluxes playing a secondary role. Under warm air advection and Föhn events in the Weddell Sea, leads and polynyas exhibit an oasis effect marked by a negative Bowen ratio, consistent with enhanced snow and ice melting. Conversely, cold air advection results in positive Bowen ratio and sea ice production. The sum of sensible and latent heat fluxes (compensation fluxes) alternates between positive and negative values. In cold-air situations, variability in net radiation is compensated by turbulent fluxes, revealing a negative feedback mechanism, while such compensation breaks down under warm-air conditions. Using the observational data, we evaluated parameterizations of energy budget components and surface albedo, deriving effective atmospheric parameters needed for bulk-flux parameterisations in numerical models and for the validation of satellite and model outputs.