A study of surface heat fluxes in the Ross Sea (Antarctica)

Abstract

In the polar regions, dynamical and thermodynamical interactions between atmosphere and ocean are strongly influenced by the presence or absence of the ice cover, which forms an insulating layer over the ocean, hindering sensible heat fluxes and forming an effective barrier to evaporation and thus preventing latent heat loss. In the framework of the CLIMA (Climatic Long-term Interactions for the Mass-balance in Antarctica) project of the Italian PNRA (National Program for Antarctic Research) we focused our attention on the evaluation of the heat fluxes between the ocean and the atmosphere in the Ross Sea, where the ice covers the sea for many months of the year. Wherever the ice cover is absent all year round, such as in leads or polynyas, the air-sea fluxes can be very large, especially in winter when the air-sea temperature differences are strong. In this work heat exchanges between sea and atmosphere, whether ice cover was present or not, were calculated from climatological data obtained from the European Centre for Medium Range Weather Forecasts, while sea ice data were collected from the US National Ice Center and National Climatic Data Center. Each of the terms in the sea surface heat budget were computed for 1994 with a temporal resolution of six hours and a spatial resolution of 0.5° using bulk formulae and obtaining monthly averaged horizontal distributions. The surface heat budget is dominated in November, December, January and February by shortwave radiation, while for the other months the turbulent and conductive heat fluxes dominate the heat exchange between the atmosphere and the sea surface. The annual total heat loss at the surface in 1994 has been estimated at about −90 W m−2 with the highest heat loss occurring close to the coast; the maximum heat loss occurred in May (−217 W m−2) while in January the heat gain by the ocean was 196 W m−2. In addition, weekly averaged values over the whole Ross Sea from 1994 to 1997 were calculated with the same parameterisation in order to study the temporal variability in this basin of each individual component and of the total surface heat budget. For this purpose only the data inside the continental shelf of the Ross Sea were considered in calculating the averaged fluxes. The 1994–97 total heat budget ranges from −87 to −107 W m−2with an average of −96 W m−2; this amount of heat loss was supposed to be compensated for by the heat advected by the Circumpolar Deep Water and its transport was estimated at about 2.9 Sv.