Extreme cyclones entering the Arctic along different tracks in winter and their related atmospheric circulation features

Extreme cyclones from mid-latitudes can transport water vapor and heat to the Arctic, change the Arctic sea ice extent and the thickness of ocean mixing layer, and bring strong winds, low temperatures, rain and snow. Using six-hourly ERA5 reanalysis data from 1980-2021, extreme cyclones, which generate in the mid-latitudes of the North Atlantic and enter the Arctic during winter, were objectively identified, detected and tracked. The 130 extreme cyclones were obtained and classified. The generation mechanisms of extreme cyclones with three kinds of tracks, i.e., West, Middle and East, and the reasons for the differences of tracks after the formation were explored. The results showed that the positive potential vorticity appeared in the lower stratosphere 5–6 days prior to the formation of the extreme cyclones, and the stratospheric positive potential vorticity intruded downward into the upper troposphere to accelerate the polar front jet, providing dynamic conditions for the formation of extreme cyclones. When the extreme cyclone is generated, the upper and lower positive potential vorticity regions are connected, which makes the cyclone develop rapidly. Additionally, it was found that the different movement tracks of the cyclones after cyclogenesis primarily depend on the transport of warm advection in the lower troposphere.