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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. 

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 In recent decades, the scintillation phenomenon at high‐latitudes characterized by “Phase without Amplitude” has become increasingly prevalent. Consequently, there is a growing tendency to focus only on the phase scintillation index in the polar region. Nevertheless, dealing with the scintillation issue solely based on the stereotype is inappropriate. In this study, we present a case study to certificate and compare the disturbances of two types of standard scintillation indices over the Canadian Arctic during a strong geomagnetic storm on 1 December 2023. Overall, all scintillation indices were elevated vigorously on the polar cap and auroral oval almost at the same time. Specifically, with the appearance of strong total electron content (TEC) gradient and fast flow, the amplitude scintillation indices () raised clearly above the background (0.05), often exceeding 0.2, however, which is still weaker than that of phase scintillation indices (, usually >0.4 radians). It evidences that at high latitudes is not so faint as to be negligible. Moreover, the less variability observed in relative to may be partially due to the Fresnel filtering effect. Therefore, the study presents the distinct disturbances of two types of scintillation indices over the polar region, challenging the popular impression of the “Phase without Amplitude” scintillation phenomenon at high latitudes and also reminding us to take a serious look at them. 

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 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 The duskside and dawnside subauroral polarization streams (SAPS) refer to high‐velocity westward and eastward plasma flows located equatorward of the auroral oval. While extensive research has focused on the duskside SAPS, the simultaneous evolution of both dawnside and duskside SAPS remains unreported. In this study, for the first time, we investigated the simultaneous evolution of duskside and dawnside SAPS using multiple Super Dual Auroral Radar Network radars during an intense storm. Observations indicate that the duskside SAPS exhibits a wider magnetic local time extension (∼7 MLT) and longer duration (∼1 hr) than the dawnside SAPS. Furthermore, the duskside SAPS resides within low‐density mid‐latitude troughs, whereas the dawnside SAPS is not located within the trough. The dawnside SAPS exhibits significantly higher electron density but comparable velocity to the duskside SAPS. These findings highlight the distinct evolution of dawnside and duskside SAPS, providing new insights into the electrodynamic processes of subauroral ionosphere and magnetosphere coupling. 

Abstract Strong Thermal Emission Velocity Enhancement (STEVE) is a latitudinally narrow, purple‐band emission observed at subauroral latitudes. Stable Auroral Red (SAR) arcs characterized by major red emission, and red/green arcs with both red and green emissions also occur at subauroral latitudes. Characteristics of magnetospheric source plasma and electromagnetic fields of these three types of arcs have not been fully understood because of the limited conjugate observations between magnetosphere and the ground. In this study, we report 11 conjugate observations (2 STEVEs, 7 SAR arcs, and 2 red/green arcs), using all‐sky images obtained at seven ground stations over more than four years from January 2017 to April 2021 and magnetospheric satellites (Arase and Van Allen Probes). We found that, in the inner magnetosphere, the source region of STEVEs and red/green arcs were located outside the plasmasphere, and that of the SAR arc was in the region of spatial overlap between the plasmasphere and ring current region. Electromagnetic waves at frequencies below 1 Hz were observed for STEVEs and red/green arcs. SuperDARN radar data showed a strong westward plasma flow in the ionosphere, especially during STEVE events, whereas the plasma flows associated with SAR arcs and red/green arcs were generally weaker and variable. The STEVE and SAR arc can appear simultaneously at slightly different latitudes and STEVEs and red/green arcs can transform into SAR arcs. These first comprehensive ground‐satellite measurements of three types of subauroral‐latitude auroras increase our understanding on similarlity, differences, and coupling of these auroras in the ionosphere and the magnetosphere. 

For decades, the Rate of Change of Total Electron Content Index (ROTI) has been employed to monitor and quantify ionospheric irregularities, serving as a potential substitute for standard scintillation indices. However, to date, ROTI has not been sufficiently investigated in terms of its relationship with standard scintillation indices. This study presents a preliminarily statistical analysis of the relationship between ROTI and standard scintillation indices using GPS receivers from the Canadian High Arctic Ionospheric Network (CHAIN) over a 5-year period from 2011 to 2015. Our results show that as ROTI increases, the phase scintillation index (σ_φ) exhibits a corresponding linear increase (slope of ∼0.34), while the amplitude scintillation index (S₄) shows little to no enhancement (slope of ∼0.05). Both relationships exhibit high correlation, with coefficients of approximately 0.93 and 0.82, respectively. The differentiated responses suggest that the significant enhancement of standard phase scintillation index is fundamentally dominated by refractive effects, which is primarily driven by large-scale ionospheric structures (>Fresnel-scale probably). The feeble inflation of S₄supports the assertion. Accordingly, the linear relationship solely between ROTI and σ_φsuggests that the increase in ROTI can be used to empirically assess the contribution of refractive variations to the enhancement of σ_φat high latitudes. 

The phenomenon known as strong thermal emission velocity enhancement (STEVE) is a narrow optical structure that may extend longitudinally for thousands of kilometers. Initially observed by amateur photographers, it has recently garnered researchers’ attention. STEVE has been associated with a rapid westward flow of ions in the ionosphere, known as subauroral ion drift (SAID). In this work, we investigate three occurrences of STEVE, using data from one of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) ground-based all-sky imagers (ASIs) located at Pinawa, Manitoba, and from the Super Dual Auroral Radar Network (SuperDARN). This approach allows us to verify the correlation between STEVE and SAID, as well as analyze the temporal variation of SAID observed during STEVE events. Our results suggest that the SAID activity starts before the STEVE, and the magnitude of the westward flow decreases as the STEVE progresses toward the end of its optical manifestation.