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Eclipse studies for the 2017 total solar eclipse over the USA benefited greatly from the vast increase in fidelity and coverage of ground-based monitoring tools, especially GNSS monitoring of total electron content (TEC). During the 2017 eclipse, total electron content (TEC) depletions up to 60% in magnitude were reported (Coster et al. 2017). These were greater than those predicted by models. Wave responses in the form of traveling ionospheric disturbances (TIDs) following this eclipse were also reported (Zhang et al., 2017). Two major solar eclipses within the 2023-2024 time frame have crossed over North America. The first was an annular solar eclipse that occurred on 14 October 2023. It began in the United States, traveling from the coast of Oregon at approximately 9 am local time (PDT) and crossed into Nevada, Utah, New Mexico before reaching the Texas Gulf Coast at approximately noon local time (CDT). During an annular eclipse, the Moon is further away from the Earth than during a total solar eclipse. Because of this, the Moon does not totally obscure the Sun during the actual eclipse and a thin ring of the Sun's surface remains visible. The reduction in solar radiation is not 100%, so the effect on the ionosphere's TEC is somewhat less than during a total eclipse. On 8 April 2024, another total solar eclipse crossed North America, passing over Mexico, the United States, and Canada. The eclipse began in the United States in Texas, and then traveled through Oklahoma, Arkansas, Missouri, Illinois, Kentucky, Indiana, Ohio, Pennsylvania, New York, Vermont, New Hampshire, and Maine before entering Canada. For both of these eclipses, we have deployed numerous GNSS receivers collecting 1-second data along the path of the eclipse. In addition, we have deployed a specialized GNSS scintillation receiver outside of Austin, TX. These GNSS TEC observations have been included in the standard Millstone Hill Geospace Facility's GNSS TEC and differential TEC processing, utilizing 2000+ receivers in the continental U.S. We report here on initial observations following both of these eclipses, including a discussion of the TEC dynamics following the path of the eclipse, the percent of observed TEC depletions, and TID analysis. Comparisons of the size of observed TEC depletions will be made with those predicted by models.
Coster et al. (Wed,) studied this question.