ULF Waves Associated With Rapid High‐to‐Low‐Latitude Transmission of Ionospheric Electric Fields During the SSC of the 10 May 2024 Storm

Abstract We present a coordinated multi‐instrument analysis of the ionospheric responses from middle to low latitudes to the storm sudden commencement triggered by an interplanetary shock (IS) on 10 May 2024. The shock arrived at ∼17:05 UT with a sudden solar wind speed increase to ∼700 km/s and a north–south interplanetary magnetic field Bz turning, driving abrupt enhancements in AE (∼1,000 nT) and SYM‐H (∼80 nT). HF Doppler data reveal a robust two‐pulse structure comprising a preliminary impulse (PI) followed by a main impulse (MI), with near‐simultaneous onset across latitudes, opposite polarities between day and night, and weak, delayed signatures on the dusk‐side. Induction magnetometers show coherent, damped quasi‐periodic ULF bursts beginning at ∼17:05:30 UT with power centered near 0.1 Hz (Pc2–3), and Swarm A detects concurrent ULF oscillations dominated by the toroidal component and near‐linear polarization. Both satellite and ground observations show polarization properties consistent with the presence of shear Alfvén waves, while co‐frequency compressional fluctuations suggest a coupling between these two wave modes. Nighttime total electron content exhibits a modest, delayed (∼50 s) ∼0.5 TECU enhancement without pronounced PI/MI fluctuations. Taken together, the available observations support a scenario in which SC‐launched Alfvén waves propagate into the ionosphere Alfvén resonator along magnetic field lines and stimulate fast mode waves at high latitudes, facilitating rapid transmission of SC‐related electric fields from high to low latitudes and producing the observed two‐pulse ionospheric signatures.