On the connection between nighttime winter ionization increase in midlatitude F2-layer and stratospheric warmings

By using the vertical sounding data and the mid-atmosphere temperature measurements from MLS Aura SHF sonde, we investigated the connection between the occurrence of abnormally high night-winter-time values of the critical frequency and stratospheric warmings. Such phenomena were revealed to develop during stratospheric warmings against an increase in the activity of planetary wave-type oscillations in the atmosphere. The interaction between planetary waves and diurnal and semidiurnal tides can increase the amplitude of semidiurnal waves that determines the nighttime ionization in the ionosphere.