Land ice loss from Antarctica is a significant and accelerating contribution to global sea-level rise; however, Antarctic mass-balance estimates are complicated by insufficient knowledge of surface mass-balance processes such as snow accumulation. These variables are challenging to observe on a continental scale and in situ data are sparse, so we largely rely on estimates from atmospheric models. Here, we employ a novel method, GPS interferometric reflectometry (GPS-IR), to measure upper (<2 m) firn-column thickness changes across a 23-station GPS array in West Antarctica. We compare the results with antenna heights measured in situ to establish the method's daily uncertainty (0.06 m) and with output from two atmospheric reanalysis products to categorize spatial and temporal variability of near-surface processes. GPS-IR is an effective method for monitoring surface mass-balance processes that can be applied to both historic GPS datasets and future experiments to provide critical in situ observations of processes driving surface-height evolution.

This study evaluates the impact of a recent upgrade in the physics package of the regional atmospheric climate model RACMO2 on the simulated surface mass balance (SMB) of the Antarctic ice sheet. The modelled SMB increases, in particular over the grounded ice sheet of East Antarctica (+44Gt a-1), with a small change in West Antarctica. This mainly results from an increase in precipitation, which is explained by changes in the cloud microphysics, including a new parameterization for ice cloud supersaturation, and changes in large-scale circulation patterns, which alter topographically forced precipitation. The spatial changes in SMB are evaluated using 3234 in situ SMB observations and ice-balance velocities, and the temporal variability using GRACE satellite retrievals. The in situ observations and balance velocities show a clear improvement of the spatial representation of the SMB in the interior of East Antarctica, which has become considerably wetter. No improvements are seen for West Antarctica and the coastal regions. A comparison of model SMB temporal variability with GRACE satellite retrievals shows no significant change in performance.