Stratosphere–troposphere synergetic effect on the extreme low-temperature event over China in late November 2022

Abstract

In late November 2022, most regions in China were hit by a strong northwest-path cold wave, bringing a high-hazard extreme low-temperature event (ELTE). Several parts of Northwest China experienced extremely low temperatures and record-breaking snow depths. A stratosphere–troposphere synergetic effect was suggested to be closely related to the ELTE according to a diagnostic analysis. On the one hand, the concurrent establishment of two blockings in Europe–Northeast Atlantic and North Pacific led to a polar vortex split at the tropopause, and the Arctic Oscillation phase subsequently turned negative. An airflow with high potential vorticity (PV) was squeezed out of the Arctic. Meanwhile, a high-PV air that originated from the lower stratospheric Arctic was conveyed southwards to the western Siberian Plain along the sloping isentropic surface. This condition triggered a tropospheric response in which the East Asia trough deepened due to the intensified cyclonic circulation induced by the high-PV intrusion. On the other hand, downward propagation of stratospheric anomalies accompanied by stratospheric polar vortex displacement and split was observed in mid- and late November, respectively. Changes in stratospheric circulation contributed to enhanced blockings over Europe–Northeast Atlantic in the lower stratosphere or upper troposphere. As a result, the inverted omega-shaped circulation pattern was formed in the middle to upper troposphere, and it consisted of the intensified East Asia trough and two blockings in the upstream and downstream regions. The high-PV air upstream of the East Asia trough was advected to China, which directly led to the outbreak of the ELTE. The establishment of double blockings and the displacement or split of the stratospheric polar vortex can be efficient signals for cold-event prediction in China. This study provides novel insights into the cause of ELTEs under warming climates in the future.