Observation of the Ionosphere in Middle Latitudes during 2009, 2018 and 2018/2019 Sudden Stratospheric Warming Events

Abstract

The ionospheric weather is affected not only from above by the Sun but also from below by processes in the lower-lying atmospheric layers. One of the most pronounced atmospheric phenomena is the sudden stratospheric warming (SSW). Three major SSW events from the periods of very low solar activity during January 2009, February 2018, and December 2018/January 2019 were studied to evaluate this effect of the neutral atmosphere on the thermosphere and the ionosphere. The main question is to what extent the ionosphere responds to the SSW events with focus on middle latitudes over Europe. The source of the ionospheric data was ground-based measurements by Digisondes, and the total electron content (TEC). In all three events, the ionospheric response was demonstrated as an increase in electron density around the peak height of the F2 region, in TEC, and presence of wave activity. We presume that neutral atmosphere forcing and geomagnetic activity contributed differently in individual events. The ionospheric response during SSW 2009 was predominantly influenced by the neutral lower atmosphere. The ionospheric changes observed during 2018 and 2018/2019 SSWs are a combination of both geomagnetic and SSW forcing. The ionospheric response to geomagnetic forcing was noticeably lower during time intervals outside of SSWs.

Responses of the African and American Equatorial Ionization Anomaly (EIA) to 2014 Arctic SSW Events

“…We investigated the responses of the equatorial/low‐latitude ionosphere over the African and American sectors to: (a) minor and major winter arctic SSW events (January–April, 2014) and (b) geomagnetic storms that occurred during the same period of the SSW events. The conclusions from this study are: In addition to the roles played by geomagnetic storms and other solar events in space weather, lower atmospheric couplings also play significant roles, particularly in the ionospheric part of space weather (ionospheric weather) (Mosna et al., 2021). With reference to the pre‐SSW quiet days, TEC intensity responded positively to the SSW peak days in both longitudinal sectors, except on February 8 in the African sector, when a negative TEC response was recorded.…”

“…In addition to the roles played by geomagnetic storms and other solar events in space weather, lower atmospheric couplings also play significant roles, particularly in the ionospheric part of space weather (ionospheric weather) (Mosna et al., 2021). With reference to the pre‐SSW quiet days, TEC intensity responded positively to the SSW peak days in both longitudinal sectors, except on February 8 in the African sector, when a negative TEC response was recorded.…”

“…In the American sector, the responses of TEC to February 19, 20 and April 12 geomagnetic storms were negative and positive to the 23 and 27 geomagnetic storms. Negative ionospheric responses are caused by a decrease in atomic oxygen density; a decrease in oxygen ion concentration and an increase in the molecular nitrogen density, leading to an increase in the loss rate to cause a decrease in the ionization density in the F‐region (Mosna et al., 2021). On the other hand, positive ionospheric responses are caused by an increase in atomic oxygen density; an increase in oxygen ion concentration and a decrease in the molecular nitrogen density, leading to an increase in the production rate to cause an increase in the ionization density in the F‐region (Mikhailov et al., 1994; Mosna et al., 2021).…”

Understanding Nighttime Ionospheric Depletions Associated With Sudden Stratospheric Warmings in the American Sector

“…Mošna et al. (2021) recently showed nighttime enhancements in the total electron content rate index over Europe during the SSWs of February 2018 and December‐January 2018‐2019 which they ascribe to both lower atmospheric and geomagnetic forcing.…”

“…Fagundes et al (2015) also reported large foF 2 variations occurring in the evening/ nighttime over South America during the major SSW of January 2009. Mošna et al (2021) recently showed nighttime enhancements in the total electron content rate index over Europe during the SSWs of February 2018 and December-January 2018-2019 which they ascribe to both lower atmospheric and geomagnetic forcing.…”