Study of Low-Latitude Ionospheric Response to the 26 August 2018 Geomagnetic Storm Using In Situ Satellite Measurements

Geomagnetic storms are the most pronounced phenomenon of space weather. The response of the Earth's ionosphere to geomagnetic storms is a rather complicated event. In this study, the low-latitude ionospheric response in the 70°-140°E geographic longitude (GLON) sector (i.e., the Asian sector) to the 26 August 2018 geomagnetic storm have been investigated by using in situ electron density (Ne) measurements probed by the Swarm satellites during the period 15 August-6 September 2018. This large geomagnetic storm began at 21 UT on 25 August 2018 and ended after 21 UT on 27 August 2018. We found that the low-latitude Ne increased dramatically on 26 August 2018 compared to that in the previous few days. Moreover, the low-latitude Ne decreased gradually since 27 August 2018, and returned to normal value on 1 September 2018. The observed positive storm effects (namely, the sudden increase of the low-latitude ionospheric Ne) on 26 August 2018 are very likely to be caused by the prompt penetration electric field (PPEF). And the gradual recovery of the low-latitude ionospheric Ne to the normal value during the period 27 August–1 September 2018 may be caused by the disturbance dynamo electric field (DDEF).