Modeling Amateur Radio Soundings of the Ionospheric Response to the 2017 Great American Eclipse

On 21 August 2017, a total solar eclipse traversed the continental United States and caused large‐scale changes in ionospheric densities. These were detected as changes in medium‐ and high‐frequency radio propagation by the Solar Eclipse QSO Party citizen science experiment organized by the Ham Radio Science Citizen Investigation (hamsci.org). This is the first eclipse‐ionospheric study to make use of measurements from a citizen‐operated, global‐scale HF propagation network and develop tools for comparison to a physics‐based model ionosphere. Eclipse effects were observed ±0.3 hr on 1.8 MHz, ±0.75 hr on 3.5 and 7 MHz, and ±1 hr on 14 MHz and are consistent with eclipse‐induced ionospheric densities. Observations were simulated using the PHaRLAP raytracing toolkit in conjunction with the eclipsed SAMI3 ionospheric model. Model results suggest 1.8, 3.5, and 7 MHz refracted at h≥125 km altitude with elevation angles θ≥22°, while 14 MHz signals refracted at h < 125 km with elevation angles θ < 10°. Plain Language Summary On 21 August 2017, the shadow of the moon traveled across the continental United States from Oregon to South Carolina during a total solar eclipse. While total eclipses are best known for their stunning visual display, they also cause changes to the ionosphere, an electrically charged layer of the upper atmosphere. These changes modify how medium‐ and high‐frequency radio waves (300 kHz to 30 MHz) travel. To help study these changes, ham radio operators communicated with each other before, during, and after the eclipse while automated monitoring systems logged their communications. These logs are compared with outputs of an eclipsed version of the ionospheric research model SAMI3. By comparing observations with the model, we can better understand how the eclipse affected both the ionosphere and radio propagation. Key Points Large‐scale citizen science experiment probes eclipse‐induced ionospheric changes Eclipse effects are observed ±0.3 hr on 1.8 MHz, ±0.75 hr on 3.5 and 7 MHz, and ±1 hr on 14 MHz Observations are consistent with an eclipse‐induced weakening of the D, E, and F ionospheric regions