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Abstract
Typhoons often occur and may cause huge loss of life and damage of infrastructures, but they are still difficult to precisely monitor and predict by traditional in-situ measurements. Nowadays, ionospheric disturbances at a large-scale following typhoons can be monitored using ground-based dual-frequency Global Positioning System (GPS) observations. In this paper the responses of ionospheric total electron content (TEC) to Typhoon Maria on 10 July 2018 are studied by using about 150 stations of the GPS network in Taiwan. The results show that two significant ionospheric disturbances on the southwest side of the typhoon eye were found between 10:00 and 12:00 UTC. This was the stage of severe typhoon and the ionospheric disturbances propagated at speeds of 118.09 and 186.17 m/s, respectively. Both traveling ionospheric disturbances reached up to 0.2 TECU and the amplitudes were slightly different. The change in the filtered TEC time series during the typhoon was further analyzed with the azimuth. It can be seen that the TEC disturbance anomalies were primarily concentrated in a range of between −0.2 and 0.2 TECU and mainly located at 135–300° in the azimuth, namely the southwest side of the typhoon eye. The corresponding frequency spectrum of the two TEC time series was about 1.6 mHz, which is consistent with the frequency of gravity waves. Therefore, the upward propagating gravity wave was the main cause of the traveling ionospheric disturbance during Typhoon Maria.
Highlights
Solar and geomagnetic activities together with geohazards may cause the oscillations of electron densities in the ionosphere
As early as 1958, Bauer [5] studied the response of the ionosphere during hurricane transit and found that the ionospheric F2-layer critical frequency increased during hurricane transit, and the frequency reached the maximum value when it was closest to the observation station
Ionospheric disturbances excited by acoustic-gravity waves triggered by two strong typhoons were detected
Summary
Solar and geomagnetic activities together with geohazards (e.g., earthquakes and typhoons) may cause the oscillations of electron densities in the ionosphere. As typical and complex strong weather systems in the lower atmosphere, typhoons can excite gravity waves and propagate to the upper layers of the ionosphere, causing several disturbances [3]. Denser Global Positioning System (GPS) observations provide important data for the study of ionospheric variations, allowing the continuous monitoring of large-scale ionospheric disturbances caused by typhoons [11,12,13,14] and earthquakes [15,16,17]. Song et al [11] used Chinese GPS station data to study two ionospheric disturbances caused by Typhoon Chan-hom and found the periods and speeds of two medium-scale traveling ionospheric disturbances (MSTIDs) to be 56 min, 268 m/s and 45 min, 143 m/s, respectively, which may have been caused by the acoustic-gravity wave excited by the super typhoon propagating upward in the ionosphere.
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