An Investigation on the Ionospheric Response to the Volcanic Explosion at Hunga Ha'apai in 2021

The Hunga Ha'apai volcano eruption (20.536 degrees S, 175.382 degrees W in Tonga), which started intermittently around December 2021 and most violently erupted on 15 January 2022, is considered to be the largest volcanic outbreak in recent decades. In this research, we derived the ionospheric total electron content (TEC) over Sanya (18.400 degrees N, 109.600 degrees E), Wuhan (30.530 degrees N, 114.610 degrees E), and Mohe (53.500 degrees N, 122.370 degrees E), from the Global Navigation Satellite System observations. Then we investigated the coupling between the volcano eruption and ionosphere through the TEC variations. The TEC anomaly decayed from about 10 days before main eruption of the Hunga Ha'apai volcano, and showed obvious fluctuations during the eruption phase. The TEC anomaly propagated periodically, with its autocorrelation-analyzed period of about 16.5 hr during the intermittent outbreak and about 8 hr during the main outbreak phase. Its independently derived wavelet-analyzed periods are about 9.4 hr during the intermittent outbreak and about 9.4 and 18.8 hr during the main outbreak phase. The propagation is mainly expressed in low frequencies, with energy concentrated in the range of 0-10(-3) Hz. This study highlights that the preeruption activities may play an important role in the coupling between the volcanic eruption and ionosphere disturbances. Plain Language Summary In this research, we study the response of ionosphere to the volcanic explosion of Hunga Ha'apai through the total electron content (TEC) over Sanya (18.400 degrees N, 109.600 degrees E), Wuhan (30.530 degrees N, 114.610 degrees E), and Mohe (53.500 degrees N, 122.370 degrees E), from the Global Navigation Satellite System. We investigated the coupling between the volcano eruption and ionosphere through the TEC variations. We found that the TEC anomalies are propagated periodically with periods of about 8-9 hr and 16-19 hr during the intermittent activity phase and the main eruptive phase, respectively. We envision that these signals probably reflect the nature of the impacts of Hunga Ha'apai volcano eruption processes on the ionosphere.