Analysis of Ionospheric Disturbances Near 120°E in the Asia‐Pacific Sector During the May 2024 Superstorm Using Multi‐Instrument Observations

Abstract On 10 May 2024, a severe G5 geomagnetic storm—the most intense of solar cycle 25—significantly disturbed the global ionosphere. This study presents a comprehensive analysis using multi‐instrument observations, including ground‐based measurements from BDS‐GEO total electron content (TEC), digital ionosondes, and magnetometers; model outputs from global ionospheric maps, HWM14, and PPEFM; and satellite data from DMSP, FY‐3E, TIMED, and Swarm. Focusing on the Asia‐Pacific sector along 120°E, the BDS‐GEO satellites provided continuous, fixed‐point monitoring of ionospheric TEC disturbances at this longitude. Hemispheric asymmetry was evident: the main phase showed weak ionospheric responses due to the local midnight conditions and plasma uplift driven by nocturnal eastward overshielding electric fields. During the recovery phase, pronounced latitudinal differentiation emerged. A persistent “delayed negative response” occurred in the Northern Hemisphere (NH) at mid‐to low‐latitudes, intensifying the following day with TEC depletions exceeding 20 TECU at multiple stations. In contrast, the Southern Hemisphere (SH) equatorial and low‐latitudes displayed a “negative‐then‐positive” disturbance pattern, accompanied by a weakened and nocturnally intensified equatorial ionization anomaly twin‐crest structure. Mechanistic analysis indicates that the observed O/N 2 depletion from TIMED/GUVI, combined with strong equatorward disturbance winds from HWM14, amplified the NH negative storms through coupled thermospheric composition changes and summer circulation. Meanwhile, SH low‐latitude disturbances were modulated by the competing effects of prompt penetration electric field and disturbance dynamo electric fields, with the background winter circulation suppressing horizontal N 2 transport while vertical motion enhanced oxygen supply, maintaining higher O/N 2 ratios. This study indicates the dominant physical mechanisms across latitudes during an extreme geomagnetic storm.