An Investigation of Extreme Cold Events at the South Pole

Abstract

Abstract From 5 July to 11 September 2012, the Amundsen-Scott South Pole station experienced an unprecedented 78 days in a row with a maximum temperature at or below -50°C. Aircraft and ground-based activity cannot function without risk below this temperature. Lengthy periods of extreme cold temperatures are characterized by a drop in pressure of around 15 hPa over four days, accompanied by winds from grid east. Periodic influxes of warm air from the Weddell Sea raise the temperature as the wind shifts to grid north. The end of the event occurs when the temperature increase is enough to move past the -50°C threshold. This study also examines the length of extreme cold periods. The number of days below -50°C in early winter has been decreasing since 1999, and this trend is statistically significant at the 5% level. Late winter shows an increase in the number of days below -50°C for the same period, but this trend is not statistically significant. Changes in the Southern Annular Mode, El Niño Southern Oscillation, and the Interdecadal Pacific Oscillation/Tripole Index are investigated in relation to the initiation of extreme cold events. None of the correlations are statistically significant. A positive Southern Annular Mode and a La Niña event or a central Pacific El Niño Southern Oscillation pattern would position the upper-level circulation to favor a strong, symmetrical polar vortex with strong westerlies over the Southern Ocean, leading to a cold pattern over the South Pole.