The Two-Dimensional and Three-Dimensional Structures Concerning the Traveling Ionospheric Disturbances Over Japan Caused by Typhoon Faxai

The two-dimensional concentric traveling ionospheric disturbances (TIDs) over Japan on the landfall day of Typhoon Faxai in 2019 were detected in total electron content by the ground-based Global Navigation Satellite System observations. They propagated in the radial direction away from the typhoon eye with a horizontal velocity of ∼190 m/s, a period of ∼24 min, and a horizontal wavelength of ∼180 km. Then, we systematically investigated the corresponding three-dimensional ionospheric responses for the first time. Remarkable wavelike structures of ionospheric electron density (Ne) and inverted conic-like structures concerning the disturbed Ne (dNe) were visualized in the F region. Furthermore, the descending phase progression of dNe with increasing time was detected at 220–550 km altitudes, which powerfully revealed that the typhoon-related TIDs were dominated by the upward atmospheric gravity waves (AGWs) propagating from the troposphere into the ionospheric F2 layer. By analyzing the spatial and temporal evolutions of Ne and dNe, we postulated that the transport process of neutral wind fluctuations associated with the upward AGWs were likely responsible for generating TIDs during Typhoon Faxai. In the end, the background wind velocity was estimated based on the recovered vertical wavelength of ∼460 km and the dispersion equation of AGWs. Our results also demonstrated that the weak background wind condition is essential for gravity waves propagating in the ionosphere.