The regional climate model HIRHAM has been applied to Antarctica driven at the lateral and lower boundaries by European Reanalysis data ERA-40 for the period 1958–1998. Simulations over 4 decades, carried out with a horizontal resolution of 50？km, deliver a realistic simulation of the Antarctic atmospheric circulation, synoptic-scale pressure systems, and the spatial distribution of precipitation minus sublimation (P-E) structures. The simulated P-E pattern is in qualitative agreement with glaciological estimates. The estimated (P-E) trends demonstrate surfacemass accumulation increase at the West Antarctic coasts and reductions in parts of East Antarctica. The influence of the Antarctic Oscillation (AAO) on the near-surface climate and the surface mass accumulation over Antarctica have been investigated on the basis of ERA-40 data and HIRHAM simulations. It is shown that the regional accumulation changes are largely driven by changes in the transient activity around the Antarctic coasts due to the varying AAO phases. During positive AAO, more transient pressure systems travelling towards the continent, and Western Antarctica and parts of South-Eastern Antarctica gain more precipitation and mass. Over central Antarctica the prevailing anticyclone causes a strengthening of polar desertification connected with a reduced surface mass balance in the northern part of East Antarctica. 1. Introduction Antarctica responds to regional and global climate forcing factors. Doran et al. [1] observed a rapid surface warming on the Antarctic Peninsula and evidence of cooling elsewhere on the continent by analyzing station data from 1966 to 2000. Controversially Steig et al. [2] reported a significant warming, which extends well beyond the Antarctic Peninsula and covers most of West Antarctica. Jacobs and Comiso [3] documented declining sea ice extent in the mid and late 20th century around the Antarctic as a whole and regionally in the Amundsen and Bellingshausen Seas. Vaughan et al. [4] discussed the insufficient current knowledge of the mechanisms and spatial distribution of climate change and showed that only large-scale variations can be predicted with some degree of confidence. Connolley and O'Farrell [5] explained that with coarse resolution and simplified physics, the current generation of Global Climate Models (GCMs) do not capture regional climate change with high skill. Although GCMs constitute the primary tool for capturing the behaviour of Earth’s climate system, Regional Climate Model (RCM) systems with higher spatial and temporal resolutions can add
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