Quantitative precipitation estimation in Antarctica using different ZE-SR relationships based on snowfall classification combining ground observations by radar and disdrometer

The Antarctic Ice Sheet plays a major role in regional and global climate variability and represents, probably, the most critical factor of future sea-level rise. Snow and solid precipitation more broadly have been recognized as primary mass input for ice sheet. However, despite its fundamental role in the surface mass balance estimation, precipitation over Polar region and in the Antarctica particularly, remains largely unknown, being not well assessed by numerical weather/climate models, by ground observations and satellite measurements as well. More accurate estimations of precipitation in the Antarctic continent are desirable not only in understanding the behavior of the Antarctic Ice Sheet, but also in validating global climate and numerical weather prediction models and also in order to constrain measurements from space during validation/calibration satellite campaigns.

Recently, several observatories in Antarctica have been equipped with equipment for cloud and precipitation measurements, such as the two Italian stations “Mario Zucchelli”, Terra Nova Bay, and Concordia, in the Antarctic Plateau. At “Mario Zucchelli”, instrumentation includes 24-GHz vertical pointing radar Micro Rain Radar (MRR) and optical disdrometer. The synergetic use of such set of instruments allows for characterizing and quantifying precipitation, even if quantitative estimate of precipitation from radar is extremely demanding, especially in snowfall, because of variability microphysical features of hydrometeors.

Usually precipitation estimation methods with weather radar are based on relationships between radar equivalent reflectivity factor (Ze) and liquid equivalent snowfall rate (SR). Several relationships are reported in literature, derived from comparison between radar and ground sensors but very few are suitable for the Antarctic continent and none also considers the microphysical characterization of hydrometeors.

This work shows quantitative estimate of the Antarctic precipitation for several snow episodes at the Mario Zucchelli station using specific ZE-SR relationships also taking into account the snowfall classification according to dominating hydrometeor type (e.g. pristine, aggregate, dendrite, plate). Microphysical properties of precipitation are inferred by comparing radar measurements with simulations obtained from disdrometer measurements in terms of reflectivity factor. Specifically, the Ze directly derived by radar has been compared with the Ze calculated by disdrometer observations coupling particle size distributions and NASA database of hydrometeor backscattering values based on the Discrete Dipole Approximation. More challenging are estimations at Concordia, where ice particles have very small sizes and are hardly detectable by laser disdrometer, and where MRR lacks of adequate sensitivity.