Snowfall in Antarctica is a key term of the ice sheet mass budget that influences the sea level at global scale. Over the continental margins, persistent katabatic winds blow all year long and supply the lower troposphere with unsaturated air. We show that this dry air leads to significant low-level sublimation of snowfall. We found using unprecedented data collected over 1 year on the coast of Adélie Land and simulations from different atmospheric models that low-level sublimation accounts for a 17% reduction of total snowfall over the continent and up to 35% on the margins of East Antarctica, significantly affecting satellite-based estimations close to the ground. Our findings suggest that, as climate warming progresses, this process will be enhanced and will limit expected precipitation increases at the ground level.Antarctica | precipitation sublimation | katabatic wind P recipitation in Antarctica falls almost exclusively as snowfall (1). As the dominant input term, precipitation is a key component in the ice sheet mass balance, and changes to this balance can directly affect the sea level at the global scale (2-5). Over Antarctica, snowfall is still not well-quantified and less documented than elsewhere. This is partly because of the lack of measurements covering the processes from precipitation formation to ground deposition. After the recent momentum of atmospheric research in the polar regions (6) and thanks to the latest technological advances in the field of remote sensing, such measurements are starting to be regularly collected in various locations of the continent (7-9).The challenges affecting in situ snowfall observations are the extremely low temperatures and snowfall rates in the interior and the wind regime close to the coasts. Over the continental margins, persistent katabatic winds blow all year long (10, 11). They originate from the cold and dry inner continent and therefore, supply the lower troposphere with large masses of unsaturated air. Surface temperature inversion and the absence of orographic barriers allow katabatic winds to develop into some of the strongest, most persistent, and most directional near-surface winds on Earth (10-12). The effect of these winds on the transport and sublimation of snow after deposition at the surface has been studied, modeled, and quantified (13,14). This process turned out to be of primary importance for the ice sheet mass balance (3), in particular in the eastern part of the continent. The interaction of katabatic winds with snowfall, however, remains unknown, despite the importance of precipitation for the ice sheet mass balance.From November of 2015 to November of 2016, we conducted a field campaign dedicated to the monitoring of precipitation (9) at the Dumont d'Urville (DDU) station on the coast of East Antarctica (66.6628 S, 140.0014 E). We obtained unprecedented weather radar measurements of precipitation in Adélie Land by means of a scanning X-band polarimetric radar (deployed from December of 2015 to January of 2016) and a K-band vertically ...

Abstract. The first results of a campaign of intensive

Abstract. Polarimetric radar-based hydrometeor classification is the procedure of identifying different types of hydrometeors by exploiting polarimetric radar observations. The main drawback of the existing supervised classification methods, mostly based on fuzzy logic, is a significant dependency on a presumed electromagnetic behaviour of different hydrometeor types. Namely, the results of the classification largely rely upon the quality of scattering simulations. When it comes to the unsupervised approach, it lacks the constraints related to the hydrometeor microphysics. The idea of the proposed method is to compensate for these drawbacks by combining the two approaches in a way that microphysical hypotheses can, to a degree, adjust the content of the classes obtained statistically from the observations. This is done by means of an iterative approach, performed offline, which, in a statistical framework, examines clustered representative polarimetric observations by comparing them to the presumed polarimetric properties of each hydrometeor class. Aside from comparing, a routine alters the content of clusters by encouraging further statistical clustering in case of non-identification. By merging all identified clusters, the multi-dimensional polarimetric signatures of various hydrometeor types are obtained for each of the studied representative datasets, i.e. for each radar system of interest. These are depicted by sets of centroids which are then employed in operational labelling of different hydrometeors. The method has been applied on three C-band datasets, each acquired by different operational radar from the MeteoSwiss Rad4Alp network, as well as on two X-band datasets acquired by two research mobile radars. The results are discussed through a comparative analysis which includes a corresponding supervised and unsupervised approach, emphasising the operational potential of the proposed method.

Abstract. This study investigates the microphysics of winter alpine snowfall occurring in mixed-phase clouds in an inner-Alpine valley during January and February 2014. The available observations include high-resolution polarimetric radar and in situ measurements of the ice-phase and liquidphase components of clouds and precipitation. Radar-based hydrometeor classification suggests that riming is an important factor to favor an efficient growth of the precipitating mass and correlates with snow accumulation rates at ground level. The time steps during which rimed precipitation is dominant are analyzed in terms of temporal evolution and vertical structure. Snowfall identified as rimed often appears after a short time period during which the atmospheric conditions favor wind gusts and updrafts and supercooled liquid water (SLW) is available. When a turbulent atmospheric layer persists for several hours and ensures continuous SLW generation, riming can be sustained longer and large accumulations of snow at ground level can be generated. The microphysical interpretation and the meteorological situation associated with one such event are detailed in the paper. The vertical structure of polarimetric radar observations during intense snowfall classified as rimed shows a peculiar maximum of specific differential phase shift K dp , associated with large number concentrations and riming of anisotropic crystals. Below this K dp peak there is usually an enhancement in radar reflectivity Z H , proportional to the K dp enhancement and interpreted as aggregation of ice crystals. These signatures seem to be recurring during intense snowfall.