Analysis of ionospheric and geomagnetic fields changes in Thailand during the May 2024 geomagnetic storm

• This study investigates changes in the equatorial ionosphere and geomagnetic field using data from Thailand during the most intense geomagnetic storm in over 20 years, occurring in May 2024. • The geomagnetic field in Thailand exhibited immediate, significant changes followed by intense fluctuations, driven by variations in the interplanetary magnetic field (IMF) and interplanetary electric field (IEF). • While the ionosphere’s virtual height (foF2) dropped almost suddenly after the onset, the ionospheric response, measured through TEC, and foF2, showed a delay by approximately 45 minutes to one hour. • The storm caused an asymmetric equatorial ionization anomaly (EIA) structure, with enhanced TEC in the southern hemisphere during its recovery phase. • Pearson correlation analysis revealed a strong coupling between the IMF and local geomagnetic fields. The extreme geomagnetic storm of May 2024, the most severe in two decades of space weather history up to date, had widespread effects on the ionosphere, from the polar regions to the magnetic equator. This study examines the responses of the equatorial ionosphere and geomagnetic field over Thailand during this geomagnetic storm, utilizing data from GNSS receivers, magnetometers, and ionosondes near the magnetic equator and low-latitude regions of Thailand. We analyze the direct and indirect impacts of interplanetary magnetic field (IMF) and interplanetary electric field (IEF) variations, driven by solar storms, on local equatorial magnetic fields and ionospheric parameters. Our finding reveals that storm-driven electric fields, particularly prompt penetration electric fields (PPEF) and disturbance dynamo electric fields (DDEF), strongly influenced equatorial electric field (EEF), causing notable fluctuations in total electron content (TEC), critical frequency of F2 (foF2), and virtual height of F layer (h’F). The Pearson correlation analysis highlights the rapid coupling between interplanetary magnetic field (IMF) and local equatorial magnetic fields during geomagnetic storms. These observations enhance our understanding of geomagnetic storm impacts in equatorial regions, which is crucial for improving space weather forecasting and mitigation strategies, especially for GNSS-dependent systems and radio communications.