Prediction of Severe Synoptic Events in Coastal East Antarctica

Abstract

The coastal region of the Antarctic continent is renowned for the frequent, intense blizzards and associated extreme weather that affect it, creating treacherous conditions that place human activities there in often perilous situations. The understanding and prediction of these events are therefore vital for continued safe operations on the continent. Severe wind events are investigated at two Australian coastal sites, Casey and Mawson. A summer case study at Casey and then the climatology of the events at the two stations are studied using station observations and atmospheric analyses. All events are found to be associated with extratropical cyclones that move close to the stations and lead to strong winds and heavy cloud cover. Most events see the passage of a high pressure ridge over the station ahead of the cyclone that blocks the cyclone, forcing it to move farther south close to the coast, thus intensifying the effect of the cyclone on the coastal weather. The ridge also produces calm, clear conditions that allow a pool of cold air to develop inland over the ice sheet. The approach of the cyclone then disrupts the stability of the surface layer inland, and at Mawson, where the katabatic flow is important, strong downslope flow can then add to the severity of the event. Station observations and reanalyses have then been used to investigate the degree to which precursors can be used to predict station wind speeds. Local conditions do not provide useful information on the development of severe winds 24 h later, but patterns in the large-scale circulation and temperature distributions offer potential for predicting the events. Regression analysis with these precursors is used to predict station wind speeds and is successful for many severe wind events, showing that the large-scale atmospheric forcing is dominant in most cases. However, there are cases where the evolution of the circulation and temperatures are more complicated than the typical events described above, and precursors are not sufficient to predict the onset of severe winds.