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. The Antarctic ice sheet mass balance is a major component of the sea levelbudget and results from the difference of two fluxes of a similar magnitude:ice flow discharging in the ocean and net snow accumulation on the ice sheetsurface, i.e. the surface mass balance (SMB). Separately modelling icedynamics and SMB is the only way to project future trends.In addition, mass balance studies frequently use regional climate models(RCMs) outputs as an alternative to observed fields because SMB observationsare particularly scarce on the ice sheet. Here we evaluate new simulations ofthe polar RCM MAR forced by three reanalyses, ERA-Interim, JRA-55, and MERRA-2,for the period 1979–2015, and we compare MAR results to the last outputs ofthe RCM RACMO2 forced by ERA-Interim. We show that MAR and RACMO2 performsimilarly well in simulating coast-to-plateau SMB gradients, and we find nosignificant differences in their simulated SMB when integrated over the icesheet or its major basins. More importantly, we outline and quantify missingor underestimated processes in both RCMs. Along stake transects, we show thatboth models accumulate too much snow on crests, and not enough snow invalleys, as a result of drifting snow transport fluxes not included in MARand probably underestimated in RACMO2 by a factor of 3. Our results tendto confirm that drifting snow transport and sublimation fluxes are muchlarger than previous model-based estimates and need to be better resolved andconstrained in climate models. Sublimation of precipitating particles inlow-level atmospheric layers is responsible for the significantly lowersnowfall rates in MAR than in RACMO2 in katabatic channels at the ice sheetmargins. Atmospheric sublimation in MAR represents 363  Gt yr−1 over the grounded ice sheet for the year 2015, which is 16 %of the simulated snowfall loaded at the ground. This estimate is consistentwith a recent study based on precipitation radar observations and is morethan twice as much as simulated in RACMO2 because of different timeresidence of precipitating particles in the atmosphere. The remaining spatialdifferences in snowfall between MAR and RACMO2 are attributed to differencesin advection of precipitation with snowfall particles being likely advected toofar inland in MAR.

Estimation of the Antarctic surface mass balance using the regional climate model MAR (1979–2015) and identification of dominant processes