Super Equatorial Plasma Bubbles and X‐Pattern Merging of Equatorial Ionization Anomaly During the 19–20 January 2026 Geomagnetic Storm

This study investigates the rare coincidence of super equatorial plasma bubbles (EPBs) and X‐pattern morphology of the equatorial ionization anomaly (EIA) over Atlantic‐American longitudes during a strong geomagnetic storm on 19–20 January 2026. The analysis incorporates ground‐based observations from Global Navigation Satellite System receivers, ionosonde, and a Fabry‐Perot Interferometer, space‐based observations from the GOLD, Swarm, and COSMIC‐2 satellites, along with modeled equatorial electric field data sets. The main results are summarized as follows: (a) The interplanetary magnetic field (IMF) Bz underwent strong southward dips to approximately −60 nT, followed by a sharp northward reversal to +60 nT, corresponding to an exceptional total variation of 120 nT. (b) Super EPBs developed rapidly in the post‐sunset sector over Atlantic longitudes after the southward turning of the IMF Bz, with plasma depletion and associated irregularities extending into unusual mid‐latitude region of 40–45 MLAT and even beyond. (c) The double EIA crests in South American longitudes exhibited a pronounced equatorward retraction after the northward reversal of the IMF Bz, merging into a single equatorial band and forming an X‐pattern configuration. The simultaneous appearance of super EPBs and the distinct X‐pattern EIA within a single storm event represents two sequential manifestations of a common key driver of penetration electric fields, with the rapid succession of under‐shielding and over‐shielding electric fields providing a unique precondition for them to occur in a temporally sequential and longitudinally complementary manner. These findings highlight the profound impacts of electrodynamic forcing in reshaping the regional and global ionosphere during extreme storm periods.