On the fine vertical structure of the low troposphere over the coastal margins of East Antarctica

Abstract

Abstract. In this study, 8\xa0years of high-resolution radiosonde data at nine Antarctic\nstations are analysed to provide the first large-scale characterization of\nthe fine vertical structure of the low troposphere up to 3\u2009km altitude over\nthe coastal margins of East Antarctica. Radiosonde data show a large spatial\nvariability of wind, temperature and humidity profiles, with different\nfeatures between stations in katabatic regions (e.g., Dumont d Urville and\nMawson stations), stations over two ice shelves (Neumayer and Halley\nstations) and regions with complex orography (e.g., McMurdo). At the Dumont\nd Urville, Mawson and Davis stations, the yearly median wind speed profiles\nexhibit a clear low-level katabatic jet. During precipitation events, the\nlow-level flow generally remains of continental origin and its speed is even\nreinforced due to the increase in the continent–ocean pressure gradient.\nMeanwhile, the relative humidity profiles show a dry low troposphere,\nsuggesting the occurrence of low-level sublimation of precipitation in\nkatabatic regions but such a phenomenon does not appreciably occur over the\nice shelves near Halley and Neumayer. Although ERA-Interim and ERA5\nreanalyses assimilate radiosoundings at most stations considered here,\nsubstantial – and sometimes large – low-level wind and humidity biases are\nrevealed but ERA5 shows overall better performance. A free simulation with\nthe regional polar version of the Weather Research and Forecasting model\n(Polar WRF) (at a 35\u2009km resolution) over the entire continent shows\ntoo-strong and too-shallow near-surface jets in katabatic regions especially\nin winter. This may be a consequence of an underestimated coastal cold air\nbump and associated sea–continent pressure gradient force due to the coarse\n35\u2009km resolution of the Polar WRF simulation. Beyond documenting the\nvertical structure of the low troposphere over coastal East Antarctica, this\nstudy gives insights into the reliability and accuracy of two major\nreanalysis products in this region on the Earth. The paper further underlines\nthe difficulty of modeling the low-level flow over the margins of the ice\nsheet with a state-of-the-art atmospheric model.