Abstract. The study of the recent variability and the future projections of the poles’ climate currently relies on polar-oriented Regional Climate Models (RCMs). However, RCMs are subject to biases and systematic errors that impact the results of their simulations. Remote Sensing (RS) data can help to reduce these ambiguities by providing indirect observations to the modeled estimates. Using the behavior of radiofrequency signals with regard to the presence of water in a snowpack, passive and active microwave instruments such as AMSR2, ASCAT, and Sentinel-1 are used to detect melt at the surface of the snowpack. In this paper, we investigate the sensitivity of the RCM “Modèle Atmosphérique Régional” (MAR) to the assimilation of surface melt occurrence estimated by RS datasets. The assimilation is performed by nudging the MAR snowpack temperature to match the observed melt state by satellite. The sensitivity is tested by modifying parameters of the assimilation: (i) the depth to which MAR snowpack is warmed up or cooled down (corresponding to the penetration depth of the satellites) to match with satellite, and (ii) the quantity of water required into the snowpack to qualify a MAR pixel as melting or not, and (iii) by assimilating multiple RS datasets. The data assimilation is performed over the Antarctic Peninsula for the 2019-2021 period. The results show an increase in the melt production (+66.7 % on average, or +95 Gt) going along with a small decrease in surface mass balance (SMB) (-4.5 % on average, or -20 Gt) for the 2019–2020 melt season. The model is sensitive to the three parameters tested but with different orders of magnitude. The sensitivity to the assimilated dataset is reduced by using multiple datasets during the assimilation and discarding the remote observations that are not coherent. For the other two parameters, the penetration depth has more impact on the assimilation than the quantity of liquid water used as melt threshold. The first one is especially sensitive for the sensors with a shorter penetration depth. In the first centimeters, a densification due to a refreeze can impact the melt production and cause an overestimation of the melt production. For the second threshold, the impact is more important on the number of melt days rather than the melt production itself. The values tested for the quantity of liquid water required into the snowpack to qualify a MAR pixel as melting or not (0.1 or 0.2 % of the snowpack mass being water) are lower than during typical melt days (~1.2 %) and impact results mainly at the beginning and end of the melt period when lower values are reached. Such an assimilation will allow an uncertainty estimation of MAR’s melt production, as well as identifying potential issues at the snowpack surface processes.

<p>Some of the highest specific mass change rates in Antarctica are reported for the Antarctic Peninsula. However, the existing estimates for the northern Antarctic Peninsula (<70°S) are either spatially limited or are affected by considerable uncertainties. Within this study, the first assessment of the geodetic mass balance throughout the ice sheet of the northern Antarctic Peninsula is carried out employing bi-static SAR data from the TanDEM-X satellite mission. Repeat coverages from austral-winters 2013 and 2017 are employed. An overall coverage of 96.4% of the study area by surface elevation change measurements is revealed. The spatial distribution of the surface elevation and mass changes points out, that the former ice shelf tributary glaciers of the Prince-Gustav-Channel, Larsen-A&B, and Wordie ice shelves are the hotpots of ice loss in the study area, and highlights the long-lasting dynamic glacier adjustments after the ice shelf break-up events. The highest mass change rate is revealed for the Airy-Seller-Fleming glacier system and the highest average surface elevation change rate is observed at Drygalski Glacier. The comparison of the ice mass budget with anomalies in the climatic mass balance indicates, that for wide parts of the southern section of the study area the mass changes can be partly attributed to changes in the climatic mass balance. The previously reported connection between mid-ocean warming along the southern section of the west coast and increased frontal glacier recession does n</p>

Abstract. Some of the highest specific mass change rates in Antarctica are reported for the Antarctic Peninsula. However, the existing estimates for the northern Antarctic Peninsula (< 70° S) are either spatially limited or are affected by considerable uncertainties. The complex topography, frequent cloud cover, limitations in ice thickness information, boundary effects, and uncertain glacial-isostatic adjustment estimates affect the ice sheet mass change estimates using altimetry, gravimetry, or the input-output method. Within this study, the first assessment of the geodetic mass balance throughout the ice sheet of the northern Antarctic Peninsula is carried out employing bi-static SAR data from the TanDEM-X satellite mission. Repeat coverages from austral-winters 2013 and 2017 are employed. An overall coverage of 96.4 % of the study area by surface elevation change measurements and a total mass budget of −24.1 ± 2.8 Gt/a is revealed. The spatial distribution of the surface elevation and mass changes points out, that the former ice shelf tributary glaciers of the Prince-Gustav-Channel, Larsen-A&amp;B, and Wordie ice shelves are the hotpots of ice loss in the study area, and highlights the long-lasting dynamic glacier adjustments after the ice shelf break-up events. The highest mass change rate is revealed for the Airy-Seller-Fleming glacier system of −4.9 ± 0.6 Gt/a and the highest average surface elevation change rate of −2.30 ± 0.03 m/a is observed at Drygalski Glacier. The comparison of the ice mass budget with anomalies in the climatic mass balance indicates, that for wide parts of the southern section of the study area, the mass changes can be partly attributed to changes in the climatic mass balance. However, imbalanced high ice discharge drives the overall ice loss. The previously reported connection between mid-ocean warming along the southern section of the west coast and increased frontal glacier recession does not repeat in the pattern of the observed glacier mass losses, excluding Wordie Bay. The obtained results provide information on ice surface elevation and mass changes for the entire northern Antarctic Peninsula on unprecedented spatially detailed scales and high precision and will be beneficial for subsequent analysis and modeling.

Figure S 1. Cumulated surface melt production (Gt) for the 2020-2021 melt season as modeled by MAR without assimilation (M AR ref in light red), with data assimilation (Assim member in dashed lines), and their averaged value (Assimmean in blue). Shaded areas represent the range of the assimilations.

Antarctica is the largest potential contributor to sea-level rise and needs to be monitored. It is also one of the first victims of global warming. However, it is often difficult to obtain high-resolution data on this vast and distant continent. Thanks to the Copernicus space program providing free and open access to high-quality data, this paper aims to show the complementarity between Sentinel-1 images and Modèle Atmosphérique régional (MAR) data over Antarctica. This study is conducted over Roi Baudouin Ice Shelf. The complementarity between the two datasets is established by a quantitative, temporal, and spatial comparison of the amplitude information of the radar signal and several variables modelled by MAR. Comparisons show strong spatial correlations between MAR variables representing melt and the backscatter coefficient recorded by the satellite. While temporal and quantitative analyses also give impressive results, further investigations are required to explain contrasting behaviors in other different areas of the ice shelf.