Vertical and Oblique Ionosphere Sounding During the 21 August 2017 Solar Eclipse

On 21 August 2017, a total solar eclipse crossed North America. Two Vertical Incident Pulsed Ionospheric Radar ionosondes were operated, one deployed under totality at Lusk, Wyoming, and another south of totality, 313 km away from the geomagnetic meridian in Boulder, Colorado. The two Vertical Incident Pulsed Ionospheric Radar systems were synchronized for precise observation of both vertical and oblique group and phase paths. Hand-scaled values of virtual heights and critical frequencies are presented. Arrival angles were computed using phase interferometry and used to compute equivalent vertical critical frequencies at the oblique midpoint. Oblique propagation geometry and horizontal gradients allowed measurement of F2 layer during ionosphere G condition where foF1 exceed foF2 after totality. Plain Language Summary This paper presents the initial results of an experiment to measure the effect on the Earth's ionosphere of the North American 21 August 2017 total solar eclipse. The ionosphere is created by solar radiation and the sudden disappearance of this energy is an opportunity to study how the ionosphere behaves under these conditions. Unique to this experiment was the ability to have two highly advanced high-frequency radars, or ionosondes, with one deployed into the totality region in Wyoming and another just outside totality in Colorado, operating from 1.5 to 12 MHz radio frequency. These instruments reflect radio waves off of the ionosphere to measure its height and density. The radars were synchronized to provide rapid measurements both overhead and between the two instrument locations. High time resolution data were manually analyzed using traditional techniques. The overall response of the ionosphere is presented and compared with previous measurements and recent predictions.