Ionospheric Vertical Disturbances Induced by Lithospheric Activities: Insights from Radio Occultation Technique

Disturbances occurring near the Earth's surface, such as earthquakes, tsunamis, volcanic eruptions, typhoons, and hurricanes, can trigger severe perturbations or fluctuations in the ionosphere. These perturbations or fluctuations typically have periods of tens of minutes and propagate outward from their origin at speeds of several hundred to thousands of meters per second. Most previous studies have utilized Total Electron Content (TEC) observations from dense ground-based Global Navigation Satellite System (GNSS) receiver networks to monitor the horizontal propagation of these perturbations or fluctuations. On the other hand, these disturbances or fluctuations also propagate vertically upward, penetrating the atmosphere and disturbing the ionosphere. Several studies have employed multiple ground-based instruments, such as seismometers, infrasound systems, magnetometers, high-frequency Doppler sounding systems, ground-based GNSS receivers, and ionosondes, to detect and investigate the vertical propagation of these perturbations. These studies have demonstrated the importance and complexity of disturbances originating from the lithosphere. Due to the scarcity of instruments primarily installed on land, observing and studying vertical disturbances remain challenging. Therefore, radio occultation (RO) techniques on Low Earth Orbit (LEO) satellites, which globally detect atmospheric and ionospheric structures, provide valuable insights for monitoring and studying phenomena in regions lacking ground-based instruments, such as oceans, deserts, and polar areas. This presentation introduces the use of RO techniques from the FORMOSAT-3/COSMIC (F3/C) and FORMOSAT-7/COSMIC-2 (F7/C2) missions to monitor ionospheric vertical disturbances caused by events such as the magnitude 9.0 Tohoku earthquake on 11 March 2011, the magnitude 7.8 Nepal earthquake on 25 April 2015, and the underwater volcanic eruption near Tonga on 15 January 2020, etc. The results show that intense disturbances originating from the lithosphere should be regarded as significant drivers that alter ionospheric structures and dynamics. Studying vertical disturbances benefits us understand the propagation of fluctuations and dynamic changes across various geospheres.