Strong Warming Over the Antarctic Peninsula During Combined Atmospheric River and Foehn Events: Contribution of Shortwave Radiation and Turbulence.

The Antarctica Peninsula (AP) has experienced more frequent and intense surface melting recently, 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. Focusing on the more intense 2022 case, this study uses high‐resolution Polar WRF simulations with advanced model configurations, Reference Elevation Model of Antarctica topography, and observed surface albedo to better understand 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 and dominated surface melting during the daytime, especially after the peak of the AR/foehn events. 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. Plain Language Summary: On the Antarctic Peninsula (AP), when ice shelves break up, glaciers flow faster from the land into the sea, leading to ice loss and increasing sea level rise. Surface warming is projected to double by 2050 over Antarctica and may have led to ice shelf collapse. Two phenomena that enhance surface warming are atmospheric rivers, (long corridors of moisture in the atmosphere) and leeside foehn effects (cooler and moist air advection on the upwind side that becomes warmer and drier when descending on the leeside). Here we study two combined atmospheric river and foehn events that led to surface warming on the AP, occurring in December 2018 and February 2022. The main warming mechanism in the northeastern AP during the nighttime was transfer of heat from the air to the ice surface (sensible heat flux), while the main mechanism during the daytime was intense sunlight, which was able to reach the surface because of clear skies on the opposite (lee) side caused by foehn. However, complicating the picture, there are gaps in the AP mountain range that let the atmospheric river through, allowing clouds to form on the other side, which then blocked some of the sunlight. Key Points: This study investigates the atmospheric river and foehn warming over the Antarctic Peninsula via observations and model simulationsAtmospheric rivers led to stronger precipitation on the upwind side and favored the foehn‐related sensible heat transfer on the leesideUnder the combined atmospheric rivers and foehn, shortwave radiation contributed the most to the ice surface warming, followed by sensible heat flux [ABSTRACT FROM AUTHOR]