The objective of this study is to compare the characteristics of sudden stratospheric warming events at altitudes of 30 and 40 km for the period from 1958 to 2023. They were determined by using the Japanese 55-year meteorological reanalysis JRA-55 to search for extreme rate of change in temperature and wind. The onset and end times of warmings were identified as the moments of zero values ​​of the second derivatives of temperature and zonal velocity averaged over latitudes 60º - 90° N at altitudes of 30 km and 40 km. These moments correspond to the extreme values ​​of the rate of change of these parameters. Over the 66-year period, 151 and 158 mid-winter warmings were detected at altitudes of 30 km and 40 km, respectively, which corresponds to 2.3-2.4 events per year, in average. The number and types of warming events may vary at different altitudes. The analyzed interval was divided into two 33-year subintervals, 1958-1990 and 1991-2023. A comparison of these intervals revealed that the number of warming events over the past 33 years has decreased by 3 and 4 events at altitudes of 30 km and 40 km, respectively. This corresponds to a decrease from approximately 2.3-2.5 events per year to 2.1-2.3 events per year. Warming duration has increased by an average of 1-3 days at altitudes of 30 - 40 km. At 30 km, the number of major warming events increased, while at 40 km, this number remained unchanged. The temperature increment during warmings increased by 1-2 K. The moments of maximum temperature increase precede, on average, the moments of most rapid decrease in zonal wind at the onset of warming events by a day. It has been confirmed that the development of warmings is always preceded by increases in the meridional heat flux directed toward the North Pole, which can contribute to the heating of the polar stratosphere and to the development of the warmings. This study were supported by the Russian Science Foundation (grant No. 25-17-00166).
 

Sudden stratospheric warming,climate change,climatology