INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 21: 21–36 (2001) THE INFLUENCE OF LARGE-SCALE ATMOSPHERIC CIRCULATION ON THE SURFACE ENERGY BALANCE OF THE KING GEORGE ISLAND ICE CAP MATTHIAS BRAUN a, *, HELMUT SAURER a , STEFFEN VOGT a , JEFFERSON CARDIA SIMO  ES b and HERMANN GOßMANN a a Institut fu ¨r Physische Geographie, Uniersita ¨t Freiburg, Werderring 4, D-79085 Freiburg, Germany b Laborato ´rio de Pesquisas Anta ´rticas e Glaciolo ´gicas, Departamento de Geografia, Uniersidade Federal do Rio Grande do Sul, A. Bento Gonc ¸ales 9500, 91501 -970 Porto Alegre, Brazil Receied 28 October 1999 Reised 7 March 2000 Accepted 8 March 2000 ABSTRACT During the austral summer 1997 – 1998 three automatic weather stations were operated at different altitudes on the sub-Antarctic ice cap of King George Island (South Shetland Islands). Snowmelt was derived from energy balance computations. Turbulent heat fluxes were calculated from meteorological measurements using the bulk aerodynamic approach, with net radiation being measured directly. Modelled ablation rates were compared with readings at ablation stakes and continuously measured snow height at a reference site. Snow depletion and daily snowmelt cycles could be well reproduced by the model. Generally, radiation balance provided the major energy input for snowmelt at all altitudes, whereas sensible heat flux was a second heat source only in lower elevations. The average latent heat flux was negligible over the entire measuring period. A strong altitudinal gradient of available energy for snowmelt was observed. Sensible heat flux as well as latent heat flux decreased with altitude. The measurements showed a strong dependence of surface energy fluxes and ablation rates on large-scale atmospheric conditions. Synoptic weather situations were analysed based on AVHRR infrared quicklook composite images and surface pressure charts. Maximum melt rates of up to 20 mm per day were recorded during a northwesterly advection event with meridional air mass transport. During this northwesterly advection, the contribution of turbulent heat fluxes to the energy available for snowmelt exceeded that of the radiation balance. For easterly and southerly flows, continentally toned, cold dry air masses dominated surface energy balance terms and did not significantly contribute to ablation. The link between synoptic situations and ablation is especially valuable, as observed climatic changes along the Antarctic Peninsula are attributed to changes in the atmospheric circulation. Therefore, the combination of energy balance calculations and the analysis of synoptic-scale weather patterns could improve the prediction of ablation rates for climate change scenarios. Copyright © 2001 Royal Meteorological Society. KEY WORDS: ablation; Antarctica; climatic change; King George Island; snowmelt; South Shetland Islands; surface energy balance; synoptic climatology 1. INTRODUCTION Large-scale weather systems are the main cause of energy exchange in the atmosphere between the mid and high latitudes. Air masses of different origins are transported over ocean or land surfaces, resulting in variable air temperature and humidity. Therefore, energy fluxes near the surface are strongly influenced by synoptic conditions. Neal and Fitzharris (1997) have pointed out that little is known about the interrelationship between large-scale atmospheric processes on the one hand, and energy exchange between atmosphere and snow and ice surfaces on the other. This knowledge, however, is a prerequisite for the downscaling and validation of general circulation models (GCMs), as well as for the estimation and prediction of possible consequences of climatic change. * Correspondence to: Institut fu ¨ r Physische Geographie, Universita ¨t Freiburg, Werderring 4, D-79085 Freiburg, Germany; e-mail: mabra@ipg.uni-freiburg.de Copyright © 2001 Royal Meteorological Society http://onlinelibrary.wiley.com/doi/10.1002/joc.563/pdf