The Altitudinal Profile of the Equatorial Ionization Anomaly Response to the Intense X9.3 Solar Flare on 6 September 2017

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The X9.3 solar flare on 6 September 2017 was the most intense of Solar Cycle 24. Based on the in situ observations from the Swarm constellation and simulations from the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model, this work explored the three‐dimensional evolution of the equatorial ionization anomaly due to the X9.3 flare. The altitudinal disturbances in the noon electron density (Ne) exhibited a “butterfly‐shaped” pattern. In the lower ionosphere (<280 km), Ne was enhanced at all latitudes, with relative/absolute increases of up to ∼40%/1.30 × 10 11 m −3 . The chemical production contribution was strongest near the lower boundary (∼200 km, peaking at 2.13 × 10 11 m −3 ) and decreased progressively with altitude to less than 10 9 m −3 at ∼550 km. The flare‐induced westward electric field drove downward E × B drifts (peaking at −3.84 m/s), resulting in bottomside Ne enhancement (1.92 × 10 10 m −3 ) and localized topside depletion (−6.79 × 10 9 m −3 ) via a reverse fountain tendency. The enhanced Ne also exhibited hemispheric asymmetry at 300 km, being stronger in the northern hemisphere (1.10 × 10 11 m −3 at 16.78° MLat, 30° geographic longitude (GLon)) than in the southern hemisphere (8.30 × 10 10 m −3 at −24.61° MLat, 22.5° GLon). This asymmetry was dominated by plasma transport via neutral winds (17.7%) and ambipolar diffusion (82.3%).