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. Calibration of SuperDARN interferometer measurements however remains challenging for several reasons, including a 2$\pi$ ambiguity in the phase 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.

Medium-scale Traveling Ionospheric Disturbances (MSTIDs) are prominent and ubiquitous features of the mid-latitude ionosphere, and are observed in Super Dual Auroral Radar Network (SuperDARN) and high-resolution Global Navigational Satellite Service (GNSS) Total Electron Content (TEC) data. The mechanisms driving these MSTIDs are an open area of research, especially during geomagnetic storms. Previous studies have demonstrated that night-side MSTIDs are associated with an electrodynamic instability mechanism like Perkins, especially during geomagnetically quiet conditions. However, day-side MSTIDs are often associated with atmospheric gravity waves. Very few studies have analyzed the mechanisms driving MSTIDs during strong geomagnetic storms at mid-latitudes. In this study, we present mid-latitude MSTIDs observed in de-trended GNSS TEC data and SuperDARN radars over the North American sector, during a geomagnetic storm (peak Kp reaching 9) on September 7-8, 2017. In SuperDARN, MSTIDs were observed in ionospheric backscatter with Line Of Sight (LOS) velocities exceeding 800 m/s. Additionally, radar LOS velocities oscillated with amplitudes reaching +/-$500 m/s as the MSTIDs passed through the fields-of-view. In detrended TEC, these MSTIDs produced perturbations reaching ~50 percent of background TEC magnitude. The MSTIDs were observed to propagate in the westward/south-westward direction with a time period of ~15 minutes. Projecting de-trended GNSS TEC data along SuperDARN beams showed that enhancements in TEC were correlated with enhancements in SuperDARN SNR and positive LOS velocities. Finally, SuperDARN LOS velocities systematically switched polarities between the crests and the troughs of the MSTIDs, indicating the presence of polarization electric fields and an electrodynamic instability process during these MSTIDs.

Propagation of high-frequency (HF) radio signals is strongly dependent on the ionospheric electron density structure along a communications link. The ground-based, HF space weather radars of the Super Dual Auroral Radar Network (SuperDARN) utilize the ionospheric refraction of transmitted signals to monitor the global circulation of E- and F-region plasma irregularities. Previous studies have assessed the propagation characteristics of backscatter echoes from ionospheric irregularities in the auroral and polar regions of the Earth’s ionosphere. By default, the geographic location of these echoes are found using empirical models which estimate the virtual backscattering height from the measured range along the radar signal path. However, the performance of these virtual height models has not yet been evaluated for mid-latitude SuperDARN radar observations or for ground scatter propagation modes. In this study, we derive a virtual height model suitable for mid-latitude SuperDARN observations using 5 years of data from the Christmas Valley East and West radars. This empirical model can be applied to both ionospheric and ground scatter observations and provides an improved estimate of the ground range to the backscatter location compared to existing high-latitude virtual height models. We also identify a region of overlapping half-hop F-region ionospheric scatter and one-hop E-region ground scatter where the measured radar parameters (e.g., velocity, spectral width, elevation angle) are insufficient to discriminate between the two scatter types. Further studies are required to determine whether these backscatter echoes of ambiguous origin are observed by other mid-latitude SuperDARN radars and their potential impact on scatter classification schemes.

An interplanetary shock can abruptly compress the magnetosphere, excite magnetospheric waves and field-aligned currents, and cause a ground magnetic response known as a sudden commencement (SC). However, the transient (<~1 min) response of the ionosphere-thermosphere system during an SC has been little studied due to limited temporal resolution in previous investigations. Here, we report observations of a global reversal of ionospheric vertical plasma motion during an SC on 24 October 2011 using ~6 s resolution SuperDARN ground scatter data. The dayside ionosphere suddenly moved downward during the magnetospheric compression due to the SC, lasting for only ~1 min before moving upward. By contrast, the post-midnight ionosphere briefly moved upward then moved downward during the SC. Simulations with a coupled geospace model suggest that the reversed E X B vertical drift is caused by a global reversal of ionospheric zonal electric field induced by magnetospheric compression during the SC.

We present a statistical investigation of the effects of interplanetary magnetic field (IMF) on hemispheric asymmetry in auroral currents. Nearly six years of magnetic field measurements from Swarm A and C satellites are analyzed. Bootstrap resampling is used to remove the difference in the number of samples and IMF conditions between the local seasons and the hemispheres. Currents are stronger in Northern Hemisphere (NH) than Southern Hemisphere (SH) for IMF B$y^+$ in NH (B$y^-$ in SH) in most local seasons under both signs of IMF B$z$. For B$y^-$ in NH (B$y^+$ in SH), the hemispheric difference in currents is small except in local winter when currents in NH are stronger than in SH. During B$y^+$ and B$z^+$ in NH (B$y^-$ and B$z^+$ in SH), the largest hemispheric asymmetry occurs in local winter and autumn when the NH/SH ratio of field-aligned current (FAC) is 1.18$\pm$0.09 in winter and 1.17$\pm$0.09 in autumn. During B$y^+$ and B$z^-$ in NH (B$y^-$ and B$z^-$ in SH), the largest asymmetry is observed in local autumn with NH/SH ratio of 1.16$\pm$0.07 for FAC. We also find an explicit B$y$ effect on auroral currents in a given hemisphere: on average B$y^+$ in NH and B$y^-$ in SH causes larger currents than vice versa. The explicit B$y$ effect on divergence-free (DF) current during IMF B$z^+$ is in very good agreement with the B$y$ effect on the cross polar cap potential (CPCP) from the Super Dual Auroral Radar Network (SuperDARN) dynamic model except at SH equinox and NH summer.

A new technique for estimating the global-scale pattern of magnetospheric convection in the ionosphere is presented. The technique uses the SuperDARN line-of-sight velocity observations combined with an empirical convection model and the assumption that the resulting velocity field is divergence free. In contrast to other techniques for convection estimation, it does not express the velocity field in terms of known basis vectors and it does not assume that the velocity can be determined from a static potential. The velocity is estimated by applying Bayesian inverse theory to the input data, model, and constraints. Linear equations for the plasma velocity at every point in the domain are solved simultaneously in a least-squares sense. Application of the technique results in convection patterns with spatial resolution equal to the calculation grid. The resulting patterns conform with expectations based on the observed IMF conditions and display features that show close correspondence to simultaneously observed features in the auroral luminosity.