GOLD Mission's Observation About the Geomagnetic Storm Effects on the Nighttime Equatorial Ionization Anomaly (EIA) and Equatorial Plasma Bubbles (EPB) During a Solar Minimum Equinox

The nighttime ionospheric response to a geomagnetic storm that occurred on 23–29 September 2020 is investigated over the South American, Atlantic, and West African longitude sectors using NASA's Global‐scale Observations of the Limb and Disk measurements. On 27 September the solar wind conditions were favorable for prompt penetration electric fields to influence the equatorial ionosphere over extended longitudes. The equatorial ionization anomaly (EIA) crests were shifted 8°–10° poleward compared to the quiet time monthly mean across ∼65°–35°W during the main phase. Ionosonde hmF2 (peak electron density height) measurements from Fortaleza (GG: 3.9°S and 38.4°W) indicated a stronger prereversal enhancement this evening than other nights. As a result, equatorial plasma bubbles (EPB) occurred at these longitudes on this evening. This is the first simultaneous investigation of EIA morphology and EPB occurrence rate over an extended longitude range from geostationary orbit during a geomagnetic storm. Plain Language Summary The effects of a geomagnetic storm that occurred during 23–29 September 2020 on the nighttime equatorial ionospheric behavior is investigated using NASA's Global‐scale Observations of the Limb and Disk (GOLD) measurements. On each evening, the equatorial ionization anomaly (EIA) crests locations and brightnesses and equatorial plasma bubbles (EPB) occurrence rates are obtained over the South American, Atlantic, and West African longitude sectors. On 27 September the solar wind conditions were favorable for the penetration of interplanetary electric fields to the equatorial ionosphere over the dusk longitude sectors (∼35°W Lon). The PPEF strengthened the pre‐reversal enhancement and thereby enhanced the plasma fountain effect. Ionospheric F2 layer height increase is confirmed by digisonde measurements at Fortaleza (GG: 3.9°S and 38.4°W). On this day, the maximum poleward shifts compared to the quiet time monthly mean values are observed across ∼65°–35°W longitude during the storm's main phase. EPBs occurrence rate was maximum on this night. The present study reports the first simultaneous investigation of EIA morphology (crests locations and brightnesses) and EPB occurrence rates over an extended longitude range during a geomagnetic storm from a geostationary orbit. Key Points First simultaneous observations of geomagnetic storm effects on equatorial ionization anomaly (EIA) morphology and equatorial plasma bubble (EPB) occurrence rate from th