Climatology and Evolution of the Antarctic Peninsula Fohn Wind-induced Melt Regime from 1979-2018

Warm and dry fohn winds on the Antarctic Peninsula (AP) cause surface melt that can destabilize vulnerable ice shelves. Topographic funneling of these downslope winds through mountain passes and canyons can produce localized wind-induced melt that is difficult to quantify without direct measurements. Our Fohn Detection Algorithm (FonDA) identifies the surface fohn signature that causes melt using data from twelve Automatic Weather Stations on the AP, used to train a machine learning model to detect fohn in 5km Regional Atmospheric Climate Model 2 (RACMO2.3p2) simulations and in the ERA5 reanalysis model. We estimate the fraction of AP surface melt attributed to fohn and possibly katabatic winds and identify the drivers of melt, temporal variability, and long-term trends and evolution from 1979-2018. We find fohn wind-induced melt accounts for 3.1% of the total melt on the AP but can be as high at 18% close to the mountains where the winds are funneled through mountain canyons. Fohn-induced surface melt does not significantly increase from 1979-2018, despite a warmer atmosphere and more positive Southern Annular Mode. However, a significant increase (+0.1Gt y-1) and subsequent decrease/stabilization occurred in 1979-1998 and 1999-2018, consistent with the AP warming and cooling trends during the same time periods. Fohn occurrence more than fohn strength drives the annual variability in fohn-induced melt. Long-term fohn-induced melt trends and evolution are attributable to seasonal changes in fohn occurrence, with increased occurrence in summer, and decreased occurrence in fall, winter, and early spring over the past 20 years.