Characteristics of Surface “Melt Potential” over Antarctic Ice Shelves based on Regional Atmospheric Model Simulations of Summer Air Temperature Extremes from 1979/80 to 2018/19

• DOI: 10.1175/jcli-d-22-0386.1
• Publication Date: 2022-10-14T20:58:41Z
• Authors: Andrew Orr; Pranab Deb; Kyle R. Clem; Ella Gilbert; David H. Bromwich; Fredrik Boberg; Steve Colwell; Nicolaj Hansen; Matthew A. Lazzara; Priscilla A. Mooney; Ruth Mottram; Masashi Niwano; Tony Phillips; Denys Pishniak; Carleen H. Reijmer; Willem Jan van de...; Stuart Webster; Xun Zou
• Keywords: 550; Snowmelt/icemelt; Ice shelves; Extreme events; 551; 530; 01 natural sciences; Climate models; 13. Climate action; SDG 13 - Climate Action; Antarctica; /dk/atira/pure/sustainabledevelopmentgoals/climate_action; name=SDG 13 - Climate Action; El Nino; 0105 earth and related environmental sciences

Abstract We calculate a regional surface “melt potential” index (MPI) over Antarctic ice shelves that describes the frequency (MPI-freq; %) and intensity (MPI-int; K) of daily maximum summer temperatures exceeding a melt threshold of 273.15 K. This is used to determine which ice shelves are vulnerable to melt-induced hydrofracture and is calculated using near-surface temperature output for each summer from 1979/80 to 2018/19 from two high-resolution regional atmospheric model hindcasts (using the MetUM and HIRHAM5). MPI is highest for Antarctic Peninsula ice shelves (MPI-freq 23%–35%, MPI-int 1.2–2.1 K), lowest (2%–3%, <0 K) for the Ronne–Filchner and Ross ice shelves, and around 10%–24% and 0.6–1.7 K for the other West and East Antarctic ice shelves. Hotspots of MPI are apparent over many ice shelves, and they also show a decreasing trend in MPI-freq. The regional circulation patterns associated with high MPI values over West and East Antarctic ice shelves are remarkably consistent for their respective region but tied to different large-scale climate forcings. The West Antarctic circulation resembles the central Pacific El Niño pattern with a stationary Rossby wave and a strong anticyclone over the high-latitude South Pacific. By contrast, the East Antarctic circulation comprises a zonally symmetric negative Southern Annular Mode pattern with a strong regional anticyclone on the plateau and enhanced coastal easterlies/weakened Southern Ocean westerlies. Values of MPI are 3–4 times larger for a lower temperature/melt threshold of 271.15 K used in a sensitivity test, as melting can occur at temperatures lower than 273.15 K depending on snowpack properties.