Characterizing the ionospheric response to the 2017 solar eclipse through raytracing analysis

On August 21, 2017 there was a total solar eclipse over the United States, offering an opportunity to study the dependence of the ionospheric density and morphology on incident solar radiation. There are significant differences between the ionospheric conditions during a solar eclipse and those normally experienced at sunset and sunrise, including the west-to-east motion of the eclipse terminator and the speed of the transition. Taken together, these factors imply that unique ionospheric responses may be witnessed during eclipses, reflected by changes in radio propagation. In order to study these changes, we ran the Super Dual Auroral Radar Network (SuperDARN) radars in Oregon and Kansas in a special mode on the eclipse day to enhance their data’s temporal and spatial resolution. These data show distinct changes in propagation during the eclipse. In order to investigate the underlying processes governing the ionospheric response to the eclipse, we employ the high frequency propagation toolbox (PHaRLAP), created by Dr. Manuel Cervera, to simulate SuperDARN data for different models of the eclipsed ionosphere. By invoking different hypotheses and comparing simulated results to SuperDARN measurements we can study the underlying processes governing the ionosphere and improve our model of ionospheric responses to an eclipse. Introduction Physics of the Ionosphere The electron density in the ionosphere varies with many factors including altitude and time of day among others. The ionosphere’s density is very dependent on sunlight. Exclusive of plasma dynamics, the continuity equation for plasma production, q, and loss, is given by the equation: αβN − αqN − βq = 0, where α and β are recombination coefficients and N is density. During an eclipse, q will decrease dramatically as the solar disk is obscured. The imbalance between production and loss should result in a decrease in electron density during the eclipse, especially at lower altitudes. At night all layers of the ionosphere experience a large decrease in electron density as shown in the figure below