Three-Dimensional Ionospheric Evolution and Asymmetry of the Electron Density Depletion Generated by the 21 June 2020 Annular Solar Eclipse

The three‐dimensional computerized ionospheric tomography (3DCIT) technique has been used to reconstruct the ionospheric response to the 21 June 2020 annular solar eclipse and the results are evaluated by constellation observing system for meteorology, ionosphere, and climate (COSMIC) observations. The 3DCIT-derived electron density (Ne) difference between the eclipse and quiet days showed that the Ne depletion was between 200-550 km and the maximum magnitude was about -3.0×10¹¹ el/m³ which was at 280 km in altitude. The contributions from below 250 and 350 km altitudes to VTEC (Vertical Total Electron Content) depletion were ~30% and ~60%, respectively. Significant asymmetry of Ne depletion with respect to the eclipse path was captured in 3DCIT results, and the deviation conditions between the Ne depletion central line and eclipse path varied at different altitudes. Simulations with the thermosphere‐ionosphere‐electrodynamics general circulation model (TIEGCM) generally showed consistent ionospheric variations with GNSS (Global Navigation Satellite System) VTEC and 3DCIT electron density. Furthermore, term analysis on the ion continuity equation indicates that the asymmetry of Ne depletion was mainly induced by the neutral wind disturbance which converged toward the eclipse region and caused opposite transport effects on both sides of the eclipse path. The thermospheric composition was also changed by disturbed neutral wind and impacted plasma production and loss rates, contributing to the Ne depletion asymmetry.