Asymmetric Ionospheric Disturbances Observed by GNSS During the 2017 Typhoon Talim and Doksuri: Origin and Characteristics

Abstract

The influence of typhoons on the ionosphere has been mentioned in many studies, while the relationship and coupling processes remain elusive. Here, we report findings on concentric ionospheric disturbance (CIDs) during typhoon Talim and Doksuri, 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 the vertical TEC obtained for each pair of satellite and receiver to obtain the perturbation component of TEC. The CIDs were observed 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 typhoons. A pattern of east-west asymmetry, that the TEC variations were significantly more pronounced in the direction opposing the background wind (eastward) compared to the direction aligned with it (westward), was observed in the CIDs. Besides, a model calculation of the electron density variation related to AGWs is used in this study. By the GAIA model, the 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.