The 2020 Siberian Heat Wave

Abstract:

An extreme Siberian temperature of +38° C at Verhojansk was observed on 20 June 2020; this followed positive Siberian temperature anomalies throughout the previous winter and spring. The Siberian heat wave of 2020 is an example of a new weather record for the subarctic that depended on the sum of continued global warming and high temperatures from random weather events. The strength and stability of the stratospheric polar vortex (SPV) over the central Arctic contributed to the winter-spring persistence of the heat wave. A similar extreme event was the loss of sea ice in Bering Sea in winter 2018 and 2019. Such events are examples of how Arctic/midlatitude weather linkages are manifest. The proximate cause for the warm Siberian events was the record strength of the SPV/tropospheric jet stream and high geopotential heights to the south that resulted in strong zonal winds from the west and reduced the potential for penetration of cold air from the north. An index of vortex strength is the Arctic Oscillation that set a positive record during February 2020 (baseline starting in 1950) and was the third and second highest in January and March. Potential vorticity of the SPV contributed to persistence. Multiple weather extremes result from a combination of background Arctic Amplification and major atmospheric dynamic events such as a strong (winter 2020) or wavy (2018 & 2019) jet stream that support regional warm or cold air advection. Such record events will not occur in a steady annual progression or in all Arctic or midlatitude locations, but one can expect that they will occasionally reoccur over the next decade. An open question is whether these dynamic events are becoming more persistent.