[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-36] Asymmetric ionospheric disturbances observed by GNSS during the 2017 typhoon: origin and characteristics

*Junxian Fu¹、Yuichi Otsuka¹ (1.Institute for Space-Earth Environmental Research, Nagoya University)

キーワード：concentric ionospheric disturbances, atmospheric gravity waves, GNSS, typhoon

The influence of typhoons on the ionosphere has been mentioned in many studies, while the exact relationship and coupling processes remain elusive. Here, we report findings on concentric ionospheric disturbance (CIDs) during typhoon TALIM and DOKSURY, using the total electron content (TEC) data derived from the Global Navigation Satellite System (GNSS) network in Taiwan. A fourth-order Butterworth bandpass filter of 8 – 20 min is applied to time series of the vertical TEC obtained for each pair of satellite and receiver to obtain perturbation component of TEC. The CIDs were observed from 06:20 to 08:00 UT on 14th September 2017, with a period of approximately 12 min and a horizontal phase velocity of 141-163 m/s. The CIDs are related to the atmospheric gravity waves (AGWs) generated by upward-moving air in the intense convective regions prompted by the typhoons. A pattern of east-west asymmetry, that the amplitude of TEC perturbations for eastward-propagating CIDs is larger than the westward, was observed in the CIDs. The TEC variations were significantly more pronounced in the direction opposing the background wind (eastward) compared to the direction aligned with it (westward), which indicates the complexity of the interactions between the ionosphere and atmospheric activities such as typhoons. Besides, a model calculation of the electron density variation related to atmospheric gravity waves is used in this study. By using data from the GAIA model, background wind direction is generally west-northwest. This asymmetry pattern is thought to be the effect of background winds on the vertical wavelength of gravity waves, leading to differences in ionospheric electron density variations in the different directions of gravity wave propagation. The results of model calculations are consistent with the TEC variations from GNSS observations.