Cause of strongest heatwave in Antarctica deciphered
The unprecedented heatwave that hit East Antarctica almost two years ago has been fully explained in a major international research effort: An intense atmospheric river from lower latitudes caused the extraordinary temperature deviation of 30 to 40°C.
In mid-March 2022, temperatures in East Antarctica rose to unprecedented levels with a record of -9.4°C on 18 March near Concordia Station on the Antarctic Plateau. Normally, temperatures at this time of year, during the transition to the Antarctic winter, are between 30 and 40°C lower. The heatwave, which lasted several days, covered an area of 3.3 million square kilometres, roughly the size of India.
This event caught the attention of the Antarctic climate research community and dozens of scientists from 14 countries joined forces to investigate the cause of the massive warm spell. In two papers published a few days ago in the Journal of Climate of the American Meteorological Society, the 54-member team reports on an intense “atmospheric river” as the cause and its effects on the Antarctic ice sheet.
An atmospheric river is a phenomenon that can occur anywhere on Earth at any time. Concentrated moisture is transported from the equatorial region to mid or high latitudes in the form of a long band about 500 kilometres wide and thousands of kilometres long. In March 2022, several cyclones over the Indian Ocean, coupled with a strongly meandering jet stream and a blocked area of high pressure along the coast of Wilkes Land, ensured that the moisture and heat was transported directly from the subtropics deep into the interior of Antarctica.
In the Arctic, too, atmospheric rivers are increasingly leading to greater melting of sea ice in summer, e.g. in 2012 and 2020, when sea ice had its lowest and second-lowest extent respectively, and to less new sea ice formation in winter.
In Antarctica, the intense atmospheric river led to the formation of a dense cloud cover over the East Antarctic Plateau, which trapped the heat in the lower atmosphere. Together with the scattered solar radiation, this eventually led to a strong warming of the surface. This was followed by a temporary but record low sea ice extent, rainfall and widespread surface melt along coastal areas, which was largely offset by heavy snowfall over the ice shelf. In addition, there was an extratropical cyclone which, in conjunction with the atmospheric river, led to the collapse of the Conger Ice Shelf, which was already unstable at the time.
Scientific research was also affected by the heatwave: Due to the high temperatures, the runways at Casey and McMurdo stations had to be closed; safety on land, ice or water was no longer guaranteed as usual; heavy precipitation reduced visibility and made outdoor activities more difficult and dangerous.
According to the research team, such an extraordinary event only occurs once every 100 years. However, climate models predict that extremes will occur more frequently in the future.
Temperatures in Antarctica currently deviate only slightly from the long-term average and are somewhat lower in some regions. Only in the Transantarctic Mountains and on the Ross Ice Shelf are temperatures currently up to 10°C above average with temperatures slightly below zero.
Julia Hager, PolarJournal
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