Energetic Electron Precipitation and Ionospheric VTEC Perturbations During the Extreme 10–11 May 2024 Geomagnetic Storm: Dominance of Electrodynamic Forcing Observed by MSS‐1A

Abstract

The coupling between inner‐belt energetic electron precipitation (EEP) and ionospheric disturbances at low‐to‐mid latitudes during extreme geomagnetic storms remains an unresolved aspect of magnetosphere‐ionosphere coupling. We investigated this coupling using high‐resolution observations from the medium‐energy electron spectrometer (MES) aboard the Macao Science Satellite‐1A (MSS‐1A), during the “Gannon Storm” of 10–11 May 2024 (minimum Dst  nT; minimum SYM‐H  nT), integrated with global vertical total electron content (VTEC) maps from the CAS Global Ionosphere Map (GIM) and magnetic field line mapping using IGRF‐13 and T96. MSS‐1A recorded intense flux enhancements (40–754 keV) penetrating to unusually low ‐shells during the storm main phase, with significant spectral hardening (power‐law index from 1.89 to 1.6), indicating deep injection and adiabatic transport into the inner magnetosphere and slot region. Concurrently, GIM observations revealed large‐scale VTEC restructuring, including storm‐enhanced density (SED) exceeding 80 TECU and poleward displacement of the equatorial ionization anomaly (EIA). While MSS‐1A confirms bounce loss cone filling at 55–507 keV, three independent lines of evidence—temporal precedence, global spatial scale, and multi‐hour persistence—demonstrate that the large‐scale VTEC response was driven by prompt penetration electric fields (PPEF) and the super‐fountain effect rather than direct EEP. Our findings show that, although EEP may enhance localized ionization in the E‐region under extreme storm conditions, its contribution to large‐scale VTEC perturbations is secondary to storm‐time electrodynamic forcing, remaining below the detection capability of current global ionospheric maps due to altitude decoupling from the F‐region and spatial‐temporal smoothing in the gridded data.