Coupling between maximum temperature and ozone levels in the lower stratosphere and extreme cooling events in Northeast China

Abstract The little studied vertical temperature structure between the lower stratosphere and the surface during extreme cooling events in Northeast China is analyzed. Minimum diurnal temperatures in Changchun (44°N, 125°E) in January 2011, 2016, 2018 and 2023 were taken from Meteostat data. NCEP–NCAR reanalysis temperatures in the meridional cross-section between the pressure levels of 1000 hPa and 10 hPa, averaged over 120–130°E, and horizontally at 30–90°N are considered. Meridional profiles of ozone concentration are based on MLS observations and ERA5 reanalysis. In January of the four winters, the temperature in Changchun dropped by 15–24°C, and the coldest days were compared to the warmest days. It has been shown that there were (i) a concerted downward movement of vertical temperature and ozone maxima to the lower stratosphere, (ii) the tropopause descent by about 2–3 km below the warmest lower stratosphere and (iii) pushing down of the cold midtropospheric layer from about 4 km to the surface with the occurrence of extremely cold weather (–28°C to –34°C). Due to the action of stationary planetary waves, the large wave ridge provides a deep southward penetration of cold polar air into Northeast China, bringing the lowest January temperature among the midlatitude regions. Our results highlight the persistent vertical structure of the thermal coupling between the lower midlatitude stratosphere and the surface over four coolings and the role of peak stratospheric temperature and ozone levels in the occurrence of extremely cold weather.