Strong Warming over the Antarctic Peninsula during Combined Atmospheric
River and Foehn Events: Contribution of Shortwave Radiation and
Turbulence
Abstract
The Antarctica Peninsula (AP) has experienced more frequent and intense
surface melting in recent years, jeopardizing the stability of ice
shelves and ultimately leading to ice loss. Among the key phenomena that
can initiate surface melting are atmospheric rivers (ARs) and leeside
foehn; the combined impact of ARs and foehn led to moderate surface
warming over the AP in December 2018 and record-breaking surface melting
in February 2022. This study uses high-resolution Polar WRF simulations
with advanced model configurations, Reference Elevation Model of
Antarctica topography information, and surface observed albedo to
improve our understanding of the relationship between ARs and foehn and
their impacts on surface warming. With an intense AR (AR3) intrusion
during the 2022 event, weak low-level blocking and heavy orographic
precipitation on the upwind side resulted in latent heat release, which
led to a more deep-foehn like case. On the leeside, sensible heat flux
associated with the foehn magnitude was the major driver during the
night and the secondary contributor during the day due to a stationary
orographic gravity wave. Downward shortwave radiation was enhanced via
cloud clearance, especially after the peak of the AR/foehn events, and
dominated surface warming over the northeastern AP during the daytime.
However, due to the complex terrain of the AP, ARs can complicate the
foehn event by transporting extra moisture to the leeside via gap flows.
During the peak of the 2022 foehn warming, cloud formation on the
leeside hampered the downward shortwave radiation and slightly increased
the downward longwave radiation.