Responses of Ionospheric TEC to Geomagnetic Storms from 1998 to 2023 in East Asia and North America

This paper investigates responses of ionospheric TEC in East Asian and North America to geomagnetic storms with 563 events during 1998–2023. Superposed epoch analysis are performed on the TEC data  aligned by each storm’s main phase onset (MPO) using superposed epoch analysis (SEA). To resolve local-time controls, storms are binned into 24 groups by the UT hour of MPO, and TEC responses are evaluated by latitude band and season. The results show that when the MPO occurs during local daytime, TEC almost invariably exhibits an immediate positive-phase disturbance; when the MPO occurs at local night, a brief and weak positive phase is typically followed promptly by a transition to a negative phase. In latitude, lower latitudes display stronger and longer-lasting positive disturbances with a later onset of the negative phase, whereas higher latitudes exhibit smaller positive amplitudes with a slightly delayed occurrence, together with an earlier onset and relatively larger magnitude of the negative phase. Seasonally, winter and the equinoxes more readily produce significant and persistent positive TEC peaks during the main phase; by contrast, in summer the main-phase positive is comparatively weak, and the recovery phase more readily begins earlier and remains negative. Our study consolidates the day–night asymmetry, latitudinal and seasonal dependence of storm-time TEC responses.