Ionospheric response to the intense geomagnetic storm of 23–24 April 2023: Insights from ground-based airglow and GPS observations over low-latitude Indian regions

In the present study, night airglow emissions from the ionosphere and mesosphere were studied using a CCD-based all-sky imager (ASI) system located at a low-latitude Indian station in Kolhapur (16.8° N, 74.2° E, dip latitude 10.6° N). We have used the OI 630 nm, OI 557.7 nm and OH emission data. We analysed night airglow emissions during the intense geomagnetic storm of 23 April 2023, the strongest of the current solar cycle, with a minimum SYM-H of –233 nT. On the night of 22 April, strong equatorial plasma bubbles (EPBs) were observed in ASI images, drifting from west to east. On the storm day (23 April), EPBs appeared at 1400 UT and abruptly disappeared by 1730 UT in the OI 630.0 nm emission. The drift velocity of EPBs ranged from 140 to 40 m/s on 22 April and from 100 to 120 m/s on the storm day (23 April), showing notable differences compared to the previous storm event of 17 March 2015 over Kolhapur, where EPB move from west to east direction generally, but it moved in reverse direction on the strong magnetically disturbed night (17 March 2015). We noted observed EPB zonal velocity follow the trend of HWM-07 model estimated velocity. The significant variations in Total Electron Content (TEC) observed during the storm’s main and recovery phases likely reflect the influence of westward Disturbance Dynamo Electric Fields (DDEFs). These results may contribute to understanding the ionospheric response to severe geomagnetic storms under the influence of westward DDEFs during the dayside recovery phase.