Ionospheric responses on the 21 August 2017 solar eclipse by using three-dimensional GNSS tomography

In this study, we have investigated the ionospheric responses on the August 2017 solar eclipse event by using a three-dimensional tomography algorithm with the ground-based GNSS (Global Navigation Satellite System) total electron content observations around Northern America. This three-dimensional ionospheric electron density structure from the tomography can provide us more information regarding the density variations and propagations of disturbances. Results show that the ionospheric electron density depletion triggered by the solar eclipse started from the higher ionosphere and then extended to lower altitudes. The maximum electron density depletion is around 40% compared with the previous day of solar eclipse. After around 30 min of the totality, the electron density continuously returned to the normal level. We further conduct a procedure of Fourier analyses to derive the vertical phase and group velocities of the electron density propagations. Results show that the opposite directions of the vertical phase and group velocities around 220–240 km altitude imply the energy/oscillation source by the solar eclipse. Graphical Abstract: [Figure not available: see fulltext.]