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Abstract An annular solar eclipse was visible on 14 October 2023 from 15:00–21:00 UT as its path traveled across North, Central, and South America. In this letter, we present the first multi‐frequency Super Dual Auroral Radar Network (SuperDARN) observations of the bottomside ionospheric response to a solar eclipse using a novel experimental mode designed for the October 2023 annular eclipse. We compare our results from the mid‐latitude Christmas Valley East radar with measurements of the vertical electron density profile from the nearby Boulder Digisonde, finding the changes in 1‐ and 2‐hop ground scatter skip distance are well correlated with the ‐layer density response, which lags the peak obscuration by 30 min. Changes in the line‐of‐sight Doppler shifts are better aligned with the time derivative of eclipse obscuration. 

Abstract The ground‐based, high‐frequency radars of the Super Dual Auroral Radar Network (SuperDARN) observe backscatter from ionospheric field‐aligned plasma irregularities and features on the Earth's surface out to ranges of several thousand kilometers via over‐the‐horizon propagation of transmitted radio waves. Interferometric techniques can be applied to the received signals at the primary and secondary antenna arrays to measure the vertical angle of arrival, or elevation angle, for more accurate geolocation of SuperDARN observations. However, the calibration of SuperDARN interferometer measurements remains challenging for several reasons, including a 2πphase ambiguity when solving for the time delay correction factor needed to account for differences in the electrical path lengths between signals received at the two antenna arrays. We present a new technique using multi‐frequency ionospheric and ground backscatter observations for the calibration of SuperDARN interferometer data, and demonstrate its application to both historical and recent data. 

Abstract This study quantifies the variation and apparent saturation of the cross polar cap potential with respect to the motional electric field in the solar wind and magnetosheath. The electric potential across the polar cap is often observed to respond linearly to solar wind driving during weak driving and nonlinearly during strong driving, with eventually responding less and less to increased driving. This effect is called “polar cap potential saturation” and has been observed in many studies that correlate some measure of solar wind driving (typically the motional electric field ) with . In this study, it is shown that measurement error in the solar wind driver creates a nonlinear bias in its variation relative to . This is accomplished by associating a decade of radar measurements of with simultaneous probabilistic predictions of in the solar wind just upstream of the bow shock and in the magnetosheath. After correcting for the bias in the solar wind and magnetosheath caused by measurement uncertainty, the extent of saturation between and the corrected solar wind is reduced. More importantly, saturates with respect to the solar wind but not the magnetosheath . This effect is caused by the magnetosheath being reduced relative to the solar wind when the solar wind Alfvén Mach number is low. Both of these findings support the theory that the saturation is due to the magnetosheath flow being magnetically dominated for large solar wind magnetic field magnitudes. 

Abstract 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 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. 

Key Points We study dusk‐dawn asymmetries in 7 years of Super Dual Auroral Radar Network convection maps which are introduced by solar wind orientations, or data processing Asymmetries due to interplanetary magnetic field B y can occur in the strength and location of the convection cells, and the return flow width Asymmetries due to the background model are likely to occur in the locations of the convection cells 

Abstract A geomagnetic storm, one of the largest in this solar cycle, was launched on 10 May 2024, producing spectacular auroral displays that could be observed across the continental United States (US) at middle and low latitudes. In this study, we focus on a brief 20‐min interval during the peak of the storm when the Sym‐H index dropped to −500 nT, and the auroral activity specified by the AL and AU indices was elevated. During this interval, the Blackstone (BKS) Super Dual Auroral Radar Network (SuperDARN) radar, observed strong ionospheric backscatter blanketing the near‐ranges across its field‐of‐view. Upon analyzing the elevation and virtual height characteristics of this backscatter we find that: (a) the BKS radar observed F‐region backscatter at unusually close ranges (750 km), and (b) this backscatter was observed over a broad range of elevation angles, including unusual very high ones. It is not physically realistic that all the radio waves, launched over a broad range of elevation angles, refract to become perpendicular to the B‐field. We therefore interpret that a sizable portion of this backscatter is produced by irregularities that are not field‐aligned. These observations show that plasma irregularities generated during strong geomagnetic storms can produce strong and unusual High Frequency (HF) radar backscatter, and significantly impact their operations. Finally, we suggest that the high‐aspect angle backscatter was most likely associated with the non‐linear decay of gradient‐drift modes that had been excited unusually strongly during the event. 

Key Points We identify changes in derived convection maps when PolarDARN and StormDARN are added, and show the impact of different processing Derived convection parameters are highly susceptible to processing variables and which radars are included We show how the number of backscatter echoes per map is critical to the integrity of the maps, and discuss how this impacts map quality