Ionospheric Changes over the Western Pacific Ocean Near and after the End of Annular Solar Eclipse on 21 June 2020.

The center path of the 21 June 2020 solar eclipse, which passed through Guam (13.62°N, 144.86°E, 94.6% obscuration), United States, at the end of its journey, provides a peculiar opportunity to study the ionospheric changes as the moon shadow moves into the nightside. In this study, remote-sensing observations of the ionosphere taken from the ionosonde, and total electron content from the International GNSS Service over Guam were analyzed to examine the related ionospheric changes. Independent in situ observations of electron density (Ne), electron (Te) and ion temperatures (Ti) from DMSP-F17 at ~850 km, and Ne and Te from Swarm-B at ~540 km were also studied. With a significant enhancement of the critical frequency and downward movement of F2-layer, the ionosphere was compressed as the moon shadow swept over Guam near its sunset hours. Neutral wind observations from the Ionospheric Connection Explorer (ICON) showed the westward reversed wind occurring in the F-region near sunset. The westward wind disturbance and downward press over the Western Pacific suggest changes in the electrodynamics in the ionosphere and thermosphere near sunset at the end of the solar eclipse, which further contributes to ~85% decrease of Ne and 157% enhancement of Te at ~540 km near midnight.