Relation of Extreme Ionospheric Events with Geomagnetic and Meteorological Activity

Abstract

This paper studies extreme ionospheric events and their relations with geomagnetic and meteorological activity. With the long observation series at the Irkutsk (52° N, 104° E) and Kaliningrad (54° N, 20° E) ionosondes we obtained the datasets of ionospheric disturbances that were treated as relative deviations of the observed peak electron density values from their 27-day running median values. As the extreme disturbances, we considered cases when the disturbance was greater than 150%. As potential sources of extreme ionospheric disturbances, we considered sudden stratospheric warmings, geomagnetic storms by the criterion Dst ≤ −30 nT, and recurrent geomagnetic storms that did not necessarily satisfy the criterion Dst ≤ −30 nT. The morphological analysis showed that the extreme ionospheric disturbance was the nighttime phenomenon that occurs from late October to early March (mainly in December–January). Considering extreme ionospheric events as nights when disturbances were greater than 150%, we obtained 25 extreme ionospheric events (on average 1.8 events per year) from the 2003–2016 Irkutsk dataset and six extreme ionospheric events (on average 0.75 events per year) from the 2009–2016 Kaliningrad dataset. The year-by-year distribution of extreme events did not reveal a clear dependence on solar/geomagnetic activity in terms of yearly mean F10.7 and Ap values but showed a correlation between the number of events and the number of recurrent geomagnetic storms. The study of the relationship between extreme ionospheric events and manifestations of geomagnetic and meteorological activity revealed that about half of extreme ionospheric events may be related to geomagnetic storms by the criterion Dst ≤ −50 nT and/or sudden stratospheric warmings. Consideration of recurrent geomagnetic storms allowed us to find the sources of almost all extreme ionospheric events. Geomagnetic activity may be considered the main cause of extreme ionospheric events at Irkutsk (mainly associated with recurrent geomagnetic storms and partly with CME-storms); while the main cause of extreme ionospheric events at Kaliningrad is not clear (a comparable contribution of sudden stratospheric warmings and storms can be assumed).