The surface energy balance during foehn events at Joyce Glacier, McMurdo Dry Valleys, Antarctica

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 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 output of the Antarctic Mesoscale Prediction System
(AMPS) on a 1.7 km grid 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 causes 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 rates are enhanced, contributing to 23 %
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, through an increase in turbulent mixing resulting from gustier and warmer
wind conditions, is largely compensated for by extra heat
losses through sublimation. Melt rates are enhanced through
an additional energy surplus from a reduced albedo during
foehn.