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We report the three-dimensional (3-D) structure of the electron depletion caused by the great solar eclipse on 21 August 2017 derived from dense Global Navigation Satellite Systems (GNSS) total electron content observations. A linear least squares inversion was performed with a continuity constraint to stabilize the solution. The reconstructed 3-D ionospheric electron density depletion showed a peak height at similar to 200 km. The depletion reached 42%, 60%, and 72%, below 250, 350, and 450 km, respectively, and the vertically integrated (150-450 km) decrease was 54%. We validated the accuracy of the electron density depletion at 200 km above the Millstone Hill observatory with the incoherent scatter radar observation and at 400 km using the in situ measurement by the Swarm satellite. The coincidence suggests that 3-D tomography is useful for investigating the vertical structure of eclipse-induced ionospheric changes. We further detected the electron depletion and enhancement with maximum values of 1.4-1.9 TECU and 0.7-1.0 TECU, respectively, in the geomagnetic conjugate region in the southern hemisphere.

Plain Language Summary The use of tens of GNSS satellites and thousands of ground GNSS receivers provided us with a rare opportunity to observe the ionospheric changes associated with the great solar eclipse in North America in August 2017. A three-dimensional tomography technique based on total electron content data was used to explore the three-dimensional structure of the ionospheric electron depletion induced by this solar eclipse. We found that a significant electron decrease occurred at a height of similar to 200 km and the decrease in the F region reached similar to 50%. We also detected simultaneous ionospheric responses to the solar eclipse in the geomagnetic conjugate region in the southern hemisphere.