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

• Main Authors: Orr, Andrew, Prenab, Deb, Clem, Kyle, Gilbert, Ella, Bromwich, D.H., Boberg, F., Colwell, Steve, Hansen, Nicolaj, Lazzara, Matthew A., Mooney, Priscilla, Mottram, Ruth H., Niwano, Masashi, Phillips, Tony, Pishniak, Denys, Tijm - Reijmer, Carleen, van de Berg, Willem Jan, Webster, Stuart, Zou, Xun
• Other Authors: Sub Dynamics Meteorology, Marine and Atmospheric Research
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: Extreme events; Antarctica; Ice shelves; El Nino; Snowmelt/icemelt; Climate models; Antarctic; Antarctic Peninsula; Pacific; Southern Ocean; Antarc*; Ice Shelves
• Online Access: https://dspace.library.uu.nl/handle/1874/428204

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.