The stratosphere-troposphere interaction during cold air outbreaks in East Asia associated with the blocking events in the extratropical Northern Hemisphere

This paper investigates the connection between large-scale blocking events and Cold Air Outbreaks (CAOs) using daily data from the ERA5 reanalysis dataset. The results show that the interannual correlation between the occurrence of large-scale blocking events and CAOs in winter (December to February of next year) tends to increase in recent years, especially in the Ural region, and the correlation is the weakest in the Okhotsk region. When a large-scale blocking event occurs in the Ural region, the upward propagation of extratropical planetary waves into the stratosphere strengthens (weakens) before the blocking with (without) CAOs within the next 10 days. The wave activity response is mainly contributed by the wave-1 component. As a result, the stratospheric polar vortex weakens (significantly strengthens) with the geopotential height over the region of (50°—70°N, 90°—110°E) gradually strengthening (weakening) after the blocking. The processes are very similar in the Baikal region, except that the wave-2 component plays a more important role than wave-1 during the 1990—2019 period when CAOs occur after the blockings.