HF Radar Observations and Modeling of the Impact of the 8 April 2024 Total Solar Eclipse on the Ionosphere‐Thermosphere System

The path of totality of the 8 April 2024 solar eclipse traversed the fields‐of‐view of four US SuperDARN radars. This rare scenario provided an excellent opportunity to monitor the large‐scale ionospheric response to the eclipse. In this study, we present observations made by the Blackstone (BKS) SuperDARN radar and a Digisonde during the eclipse. Two striking effects were observed by the BKS radar: (a) the Doppler velocities associated with ground scatter coalesced into a pattern clearly organized by the line of totality, with a reversal in sign across this line, and, (b) a delay of ∼ ${\sim} $45 min between time of maximum obscuration and maximum effect on the skip distance. The skip distance estimated using a SAMI3 simulation of the eclipse did not however capture the asymmetric time‐delay. These observations suggest that the neutral atmosphere plays an important role in controlling ionospheric plasma dynamics, which were missing in SAMI3 simulations. Plain Language Summary The total solar eclipse on 8 April 2024 was the last one to be observed over the continental United States until 2045. In addition to blocking the visible light from the Sun over a swath ranging a few hundred kilometers, a solar eclipse will also partially obscure the Sun's extreme ultraviolet radiation. As a result, an eclipse can drive significant changes in the ionosphere, a charged region in the Earth's upper atmosphere that is predominantly ionized by solar radiation. A unique feature of this eclipse was that the path of totality traversed the fields‐of‐view of three Super Dual Auroral Radar Network (SuperDARN) radars–Fort Hays East, Blackstone, and Wallops Island. SuperDARN radars operate in the High Frequency (HF) range, and radio waves in this frequency range are particularly sensitive to changes in the ionosphere. In this study, we use observations provided by SuperDARN radars alongside a Digisonde to determine the temporal response of the different ionospheric layers to the eclipse and compare these observations with modeled behavior. Key Points We present observations made by the Blackstone SuperDARN radar, a Digisonde, and SAMI3 simulations to analyze the eclipsed ionosphere SuperDARN Doppler velocities cohered into a pattern clearly organized by the line of totality with a reversal in sign across the line SuperDARN skip distance and Digisonde derived foF2 show a delayed response to the shadow, suggesting slower response at higher altitudes