The Effects of Solar Flares and Geomagnetic Storm on the Upper and Lower Ionosphere Across the Malay Archipelago Between 8th and 15th May 2024

Abstract The Mother's Day Storm is the strongest solar storm event in Solar Cycle 25 to date and has been the strongest solar storm since the Halloween storm of 2003. This event provides a great opportunity to investigate the effect of the solar storm on the upper and lower ionospheres. In this study, we investigated the response of the ionosphere to solar flares and geomagnetic storms between 8th and 15th May 2024, using very low frequency radio waves (VLF) collected by our newly built UTM‐SID VLF receiver and analyzing the Total Electron Contents (TEC), detrended TEC (dTEC), and Rate Of TEC change Index (ROTI) derived from Global Positioning Satellite System (GNSS) signals across the Malay Archipelago Region. UTM‐SID successfully detected 38 out of 114 solar flares that occurred during this period, and the detection depended on the intensity and time of the solar flare. 7 dTEC and 5 ROTI responses were noted, along with a rapid enhancement of vertical TEC (vTEC) of up to 0.5 TECU during severe solar flares. Meanwhile, the geomagnetic storm that occurred on 11–12 May had induced high dTEC and ROTI variations, with dTEC reaching 5 TECU and ROTI of 0.5 TECU/min, suggesting the occurrence of a Travelling Ionospheric Disturbance (TID). Additionally, Equatorial Plasma Bubbles (EPB) were found to be suppressed on 11 May and a pre‐sunrise EPB was noted on 12 May. Background VLF signals are also enhanced during this period.