Why have extreme low-temperature events in northern Asia strengthened since the turn of the 21st century?

Abstract

This study reveals that the intensity of cold-season (October–March) extreme low-temperature events (ELTs) during 1982–2022 strengthened after the year 2000 over northern Asia, along with a decrease in their frequency. Two significant interdecadal changes in cold-season atmospheric circulations after the year 2000 were found to be associated with these changes. Firstly, there has been an increased occurrence of extremely strong blocking highs over the North Atlantic, promoting anomalous meridional circulation. Secondly, the upper-level jet stream has weakened, reducing the polar vortex and strengthening the cold polar air that erupts southward. Statistical analysis and model experiments suggest that the positive phase of the Atlantic Multidecadal Oscillation after the year 2000 may have contributed to the strengthened ELTs by causing deep warming over the North Atlantic. The direct thermodynamic effects of deep warming intensify the blocking high over the North Atlantic. Simultaneously, an anomalous easterly wind appears in the upper troposphere due to thermal wind theory, and the weakened jet stream results in a stronger meridional flow, leading to an extremely strong blocking high.