Topside Ionospheric Disturbances Detected Using Radio Occultation Measurements During the August 2017 Solar Eclipse

The CASSIOPE (also known as Swarm-E) satellite crossed the path of totality of the August 2017 eclipse at ~640-km altitude ~10 min following the lunar umbra. Observations from CASSIOPE's Global Positioning System radio occultation receiver reveal total electron content variations of 0.2–0.3 total electron content units in the topside ionosphere—a signature of medium-scale (100-200 km) plasma disturbances in the lunar penumbra that were induced by the eclipse. The variations were only observed during the eclipse, their absence on preceding days being consistent with their very low (<10%) statistical occurrence probability. Their spectral characteristics match those of other contemporaneous measurements, and their detection is consistent with the simulated ionosphere-thermosphere response to the eclipse. To capture the small-scale size of the variations or to simulate those expected in the upcoming (July 2019) total eclipse, ionosphere-thermosphere model runs with a spatial resolution of 50 km or better would be required.