Comment on tc-2022-102

Abstract

The McMurdo Dry Valleys (MDV) are a polar desert, where glacial melt is the main source of water to streams and the ecosystem. Summer air temperatures are typically close to zero and therefore foehn events can have a large impact on the meltwater production. A 14-month record of automatic weather station (AWS) data on the Joyce Glacier is used to force a 1D surface energy balance model to study the impact of foehn events on the energy balance. AWS data and 1.7 km resolution output of the Antarctic Mesoscale Prediction System (AMPS) are used to detect foehn events at the AWS site. Foehn events at Joyce Glacier occur under the presence of cyclones over the Ross Sea. The location of Joyce Glacier on the leeward side of the Royal Society Range during these synoptic events cause foehn warming through isentropic drawdown. This mechanism differs from the foehn warming through gap-flow that was earlier found for other regions in the MDV and highlights the complex interaction of synoptic flow with local topography of the MDV. Shortwave radiation is the primary control on melt at Joyce Glacier and melt often occurs with subzero air temperatures. During foehn events, melt occurs more frequently and melt rates are enhanced, contributing to 19 % of the total annual melt. Foehn winds cause a switch from a diurnal stability regime in the atmospheric surface layer to a continuous energy input from sensible heat flux throughout the day. The sensible heating during foehn is largely compensated for by extra heat losses through sublimation, and melt rates are enhanced through an additional energy surplus from a reduced albedo.