Reassessment of the Antarctic surface mass balance using calibrated output of a regional atmospheric climate model

A detailed comparison of model-simulated and observed Antarctic surface mass balance (SMB) is presented, using output of a regional atmospheric climate model (RACMO2/ANT) for the period 1980 to 2004. All available SMB observations from Antarctica (N = 1900) are used for the comparison, except clearly erroneous observations and data which are in areas where dominant SMB patterns occur on scales smaller than the model resolution. A high correlation is found (r = 0.82), while the regression slope (1.2) indicates that the model slightly overemphasizes SMB gradients. Comparing the model SMB with the latest SMB compilation, a similarly high correlation is found (r = 0.79), but the regression slope is much too steep because model-simulated SMB agrees less with the compilation in data-sparse regions. Model-simulated SMB resembles the observed SMB as a function of elevation very well. This is used to calibrate model-simulated SMB to reassess the contemporary Antarctic SMB. Compared to the latest SMB compilation, calibrated model-simulated SMB is up to 1 m yr(-1) higher in the coastal zones of East and West Antarctica, which are without exception in areas with few observations. As a result, the SMB integrated over the grounded ice sheet (171 +/- 3 mm yr(-1)) exceeds previous estimates by as much as 15%. Support or falsification of this model result can only be found in new SMB observations from high accumulation regions.