The surface mass balance and near-surface climate of the Antarctic ice sheet in RACMO2.4p1

This study presents a new near-surface climate and surface mass balance (SMB) product for Antarctica for the historical period 1960-2023 using the updated version of the Regional Atmospheric Climate Model (RACMO), version 2.4p1 (R24). We study the impact of the major updates implemented in R24 on the climate of Antarctica and show that the SMB, surface energy budget, albedo, pressure, temperature, and wind speed compare well with observations. Compared to preceding RACMO versions, the advection of snow hydrometeors and alterations in the blowing snow parameterization affect the SMB, resulting in more precipitation in the mountains of West Antarctica and the Antarctic Peninsula and an alternating pattern of SMB changes in the coastal zones of East Antarctica. Integrated over the ice sheet, including ice shelves, the modeled SMB is 2546 Gt yr-1, with an inter-annual variability of 133 Gt yr-1. Melt fluxes are small in Antarctica, at 124 Gt yr-1 and with an inter-annual variability of 31 Gt yr-1, but can be significant on ice shelves, locally exceeding 500 mm water equivalent yr-1. The presence of melt water in snow compares remarkably well with remote sensing observations and has improved compared to the previous operational RACMO version, 2.3p2. Temperature, upward and downward shortwave radiative fluxes, and albedo are modeled well compared to in situ observations. The longwave downward radiative and turbulent fluxes, however, require further model developments.