Observation of Latitudinal Asymmetric Ionospheric Disturbances Induced by Typhoon YAGI (2024) Using the BeiDou GEO Satellite

Typhoons, as intense atmospheric disturbances, are capable of significantly influencing ionospheric conditions, primarily through the excitation of gravity waves, which transfer energy into the ionosphere. This study investigates the characteristics of ionospheric disturbances during September 1–8, 2024, when Typhoon YAGI affected the study region. Data from GNSS ground stations, COSMIC-2 LEO satellites, and GUVI/TIMED observations, in conjunction with the HWM14 horizontal wind model, were utilized to examine the coupling mechanisms between typhoons and the ionosphere. The results indicate that Typhoon YAGI induced pronounced ionospheric disturbances along its trajectory, with propagation velocities ranging from 127 m/s to 339 m/s, consistent with those of medium-scale traveling ionospheric disturbances (MSTIDs). Notably, within the fixed longitude range of 120°±5°E, the Beidou GEO TEC results based on the inversion of MEGX stations in the range of 0°N-25°N, as well as the COSMIC-2 electron density profiles, indicate that there is a clear north-south difference in the ionospheric response near the latitude of 17°N, with the northern region showing a positive response in terms of increased electron density, while the negative response in the south. In addition, the equatorial electric field (EEF) and equatorial electrojet (EEJ) analyses show that the electric and magnetic field activities remained relatively calm during the typhoon. However, on September 4, the southward turning of the IMF Bz triggered a westward PPEF, which significantly reduced the north-south asymmetry of the ionospheric response. Meanwhile, the background wind speed was estimated by the HWM14 model to be low, suggesting a relatively stable atmospheric background. The above results further reveal the coupling between AGWs and the ionosphere, as well as the modulation effect of the topography and background wind field on the disturbance propagation.