Four‐Peak Structure on Equatorial Ionization Anomaly Crests During the May 2024 Geomagnetic Storms

This study investigates the four-peak electron density structure in the Equatorial Ionization Anomaly (EIA) during the intense geomagnetic storms of 10–20 May 2024, utilizing dayside data at ∼500 km from the China Seismo-Electromagnetic Satellite (CSES-01). Observations revealed distinct four peaks in latitudinal profiles of electron density, symmetrically distributed across both hemispheres. Particularly, the poleward crests can expand beyond ±30° quasi-dipole latitude during the 10 May superstorm. To reveal the potential driver of such unique EIA structure, statistical analysis is conducted on 35 CSES-01 orbits which identified the four-peak phenomenon. The enhanced equatorial electrojet activity, inferred from the scalar magnetic field residuals, indicates that the four-peak morphology is likely related to the prompt penetration electric field (PPEF). Superposed epoch analysis also highlighted that intensification of the mean SuperMAG |SML| index preceded the onset of four-peak structures by ∼20 min, whereas the mean eastward equatorial electric field, derived from an empirical model of the interplanetary electric field driven penetration, exhibits no statistically significant enhancement, implying that substorm-associated PPEF may be the primary driver of this type of EIA structure. This study advances understanding of EIA variability under extreme space weather conditions and the findings underscore the critical role of magnetosphere-ionosphere coupling via substorm-driven electric fields in reshaping storm-time ionospheric plasma distribution.