Persistence of the Long‐Duration Daytime TEC Enhancements at Different Longitudinal Sectors During the August 2018 Geomagnetic Storm

Abstract

In this study, the ionospheric responses in the Asian-Australian, American, and African sectors during the August 2018 geomagnetic storm were investigated based on the Beidou geostationary orbit (GEO) satellite and Massachusetts Institute of Technology (MIT) Madrigal total electron contents (TECs), combined with measurements from ionosondes, magnetometers, and Global Ultraviolet Imager (GUVI). The middle-and low-latitude TECs were dominated by positive responses over the three longitudinal sectors during the storm on 26-29 August. It is unique that daytime TECs at the Asian-Australian, American, and African sectors displayed large enhancements larger than 10 TEC units (TECu) on 27-29 August, during the recovery phase, when the ionosphere is usually dominated by plasma depletions due to the ionospheric disturbance dynamo and/or disturbed thermospheric compositions. The combination and competition of the disturbed vertical plasma drifts through the solar wind-magnetosphere-ionosphere (SW-M-I) coupling and disturbed neutral compositions contribute significantly to the daytime TEC responses at different longitudinal sectors on 26 August during the main and early recovery phases. The eastward equatorial electrojet and O/N 2 during the recovery phase on 27-29 August are larger than the quiet reference, which suggest that the enhanced upward vertical plasma drifts combining with higher O/N 2 make an important contribution on the daytime positive ionospheric storm during the recovery phase. The enhanced vertical plasma drifts could not be driven by the SW-M-I coupling or ionospheric disturbance dynamo associated with the geomagnetic storm. Further studies should be untaken to explore the dominant sources for the enhanced upward vertical drifts during the recovery phase.

The Ionosphere at Middle and Low Latitudes Under Geomagnetic Quiet Time of December 2019

“…They thought that this ionospheric density enhancement is possibly attributed to the lower atmospheric forcing. Similar features are also reported during the recovery phase of the August 2018 storm and the March 2015 storm by Li et al (2020) and Kuai et al (2016), respectively. Furthermore, Liu et al (2008) analyzed ionospheric pre-storm enhancements in NmF2 and total electron content (TEC) at low latitudes and suggested that a possible cause is the zonal electric field unrelated to geomagnetic storms.…”

“…the ionosphere and thermosphere could react to geomagnetic disturbance differently due to the different solar EUV energy input. The research on the ionosphere variations during the storm or quiet time in solar minimum has also been ongoing (e.g., Cai, Burns, Wang, Coster, et al, 2020;Klenzing et al, 2013;Laskar et al, 2020;Li et al, 2020). However, some ionospheric variations/phenomena during geomagnetic storms are possibly not attributed to the energy injections from the solar wind and magnetosphere.…”

The nighttime ionospheric response and occurrence of equatorial plasma irregularities during geomagnetic storms: a case study

“…For the same storm event, Xiong et al (2019) further found that the dayside ionosphere at low-and equatorial-latitudes exhibited prominent positive and negative responses in the Asian and American longitudinal sectors, respectively, which agrees very well with the Equatorial Electrojet (EEJ) variations observed with two ground-based magnetometers located at Huancayo in Peru and Davao in the Philippines. Similar long-lasting daytime TEC enhancements at low and equatorial latitudes were observed in another storm recovery phase on 27-30 August 2018 (Li et al, 2020), but the opposite ionospheric response in Asian and American sectors as reported by Xiong et al (2019) was not observed.…”

“…For the storm in August 2018, although Li et al (2020) found in general a positive ionospheric response in the Asian sector during the storm recovery phase, different TEC perturbations were observed for the stations at different latitudes, with a much weaker positive response (or even negative) for the northern stations, e.g., the BBKD and HKWS (see their Fig. 3).…”

“…2 and 3) reveal the prominent longitudinal and storm phase dependence of storm-induced ionospheric responses. The mechanisms for causing the different patterns of the ionospheric responses are possibly due to the lower atmospheric forcing (Lei et al, 2018;Li et al, 2020;Xiong et al, 2019). However what kind of lower atmospheric forcing and the detailed mechanism to cause the topside ionospheric responses are out of the scope of this study.…”