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

In the polar regions, dynamical and thermodynamical interactions between at mosphere and ocean are strongly influenced by the presence or absence of th e ice cover, which forms an insulating layer over the ocean, hindering sens ible heat fluxes and forming an effective barrier to evaporation and thus p reventing latent heat loss. In the framework of the CLIMA (Climatic Long-te rm 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 t he Ross Sea, where the ice covers the sea for many months of the year. Wher ever 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 se a and atmosphere, whether ice cover was present or not, were calculated fro m climatological data obtained from the European Centre for Medium Range We ather 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 sur face heat budget were computed for 1994 with a temporal resolution of six h ours and a spatial resolution of 0.5 degrees using bulk formulae and obtain ing monthly averaged horizontal distributions. The surface heat budget is d ominated in November, December, January and February by shortwave radiation , while for the other months the turbulent and conductive heat fluxes domin ate the heat exchange between the atmosphere and the sea surface. The annua l 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 who le Ross Sea from 1994 to 1997 were calculated with the same parameterisatio n in order to study the temporal variability in this basin of each individu al component and of the total surface heat budget. For this purpose only th e data inside the continental shelf of the Ross Sea were considered in calc ulating the averaged fluxes. The 1994-97 total heat budget ranges from -87 to -107 W m(-2) with an average of -96 W m(-2); this amount of heat loss wa s supposed to be compensated for by the heat advected by the Circumpolar De ep Water and its transport was estimated at about 2.9 Sv.