Climatology of sudden stratospheric warmings at altitudes of 30 and 40 km using the method of extreme change rate of temperature and wind.

   The aim of this work is to compare the characteristics of sudden stratospheric warmings (SSWs) at altitudes of 30 and 40 km for the period from 1958 to 2017, which are determined with the method of extreme rate of change (MERC) of temperature and wind using the Japanese 55-year meteorological reanalysis JRA-55 data. The start and end time of the SSW is identified by the moments of zero values ​​of the second derivative of temperature and zonal velocity averaged over latitudes above 60º N at altitudes of 30 km and 40 km, which correspond to the extreme ​​rate of change of these parameters. A modified classification of SSWs types is proposed based on the characteristics obtained using the MERC method at altitudes of 30 and 40 km. The criteria for determining strong and moderate SSWs are described, which can be considered as analogs of major and minor warmings in the international SSWs classification. MERC method has increased sensitivity and made it possible to identify an additional class of weak SSWs. Early winter stratospheric warmings occurring in late autumn or early winter (November-December) are considered separately. Over a 59-year period, 140 midwinter SSWs were detected at an altitude of 30 km and 146 midwinter SSWs at an altitude of 40 km (an average of 2-3 events per year). The number of SSWs events and the types of one SSWs event may differ at different altitudes. The moments of maximum temperature growth rate are ahead, on average, by one day, of the moments of the most rapid decrease of zonal wind at the beginning of the SSW. SSWs events at an altitude of 40 km are on average more intense than at an altitude of 30 km and are shorter-lived. It has been confirmed that the development of SSWs is always preceded by increases in the meridional heat flow directed toward the North Pole, which can contribute to the heating of the polar stratosphere and the development of SSWs.