Ionospheric Anomaly and GNSS Positioning Responses to the January 2022 Tonga Volcanic Eruption

Extreme natural disasters, such as volcanic eruptions, have been demonstrated to create visible pressure waves in the atmosphere and trigger observable ionospheric wave responses that may travel hundreds of kilometers in the ionosphere, which is the ionized area of the Earth's upper atmosphere. During the Tonga volcano eruption, the acoustic and gravity waves are generated that can cause ionospheric total electron content (TEC) perturbations and variations. The TEC determines the Global Navigation Satellite System (GNSS) ionospheric delay and can cause significant positioning errors, which may affect the performance of GNSS based applications. In this paper, GNSS data collected from the Hong Kong Satellite Positioning Reference Station Network are processed to analyze the ionospheric activity and positioning performance responding to the serious Tonga volcano eruption in the southwest Pacific on 15 January 2022. The TEC Rate (TECR) and Melbourne Wubbena Wide Lane (MWWL) linear combinations are applied to detect and repair cycle slips jumps. A Savitzky-Golay low-pass filter with a 30s window is used to improve the TEC accuracy. The changes in TEC, ROTI, and positioning errors in the eastward, northward, and upward directions after the anomalous ionospheric propagation to Hong Kong between 11:30 and 14:30 were investigated. It was found that the ionospheric anomaly could generate large changes in the three parameters, with peaks up to three times the calm period. This prompt research contributes to a better understanding of the coupling of extreme ionospheric activities and dynamics caused by volcanic eruptions. It is of great significance for ionospheric modeling and prediction, which further benefits GNSS applications.