Space-based observations of the signatures associated with STEVE show how this phenomenon might be closely related to an extreme version of a SAID channel. Measurements show high velocities ($>$4km/s), high temperatures ($>$4,000 K), and very large current density drivers (up to 1$\mu$A/m$^2$). This phenomena happens in a small range of latitudes, less than a degree, but with a large longitudinal span. In this study, we utilize the GEMINI model to simulate an extreme SAID/STEVE. We assume a FAC density coming from the magnetosphere as the main driver, allowing all other parameters to adjust accordingly. We have two main objectives with this work: show how an extreme SAID can have velocity values comparable or larger than the ones measured under STEVE, and to display the limitations and missing physics that arise due to the extreme values of temperature and velocity. Changes had to be made to GEMINI due to the extreme conditions, particularly some neutral-collision frequencies. The importance of the temperature threshold at which some collision frequencies go outside their respective bounds, as well as significance of the energies that would cause inelastic collisions and impact ionization are displayed and discussed. We illustrate complex structures and behaviors, emphasizing the importance of 3D simulations in capturing these phenomena. Longitudinal structure is emphasized, as the channel develops differently depending on MLT. However, these simulations should be viewed as approximations due to the limited observations available to constrain the model inputs and the assumptions made to achieve sensible results.

STEVE (Strong Thermal Emission Velocity Enhancement) is an optical phenomenon of the sub-auroral ionosphere arising from extreme ion drift speeds. STEVE consists of two distinct components in true-color imagery: a mauve or whitish arc extended in the magnetic east-west direction, and a region of green emission adjacent to the arc, often structured into quasi-periodic columns aligned with the geomagnetic field (the “picket fence”). This work employs high-resolution imagery by citizen scientists in a critical examination of fine scale features within the green emission region. Of particular interest are narrow “streaks” of emission forming underneath field-aligned picket fence elements in the 100–110-km altitude range. The streaks propagate in curved trajectories with dominant direction toward STEVE from the poleward side. The elongation is along the direction of motion, suggesting a drifting point-like excitation source, with the apparent elongation due to a combination of motion blur and radiative lifetime effects. The cross-sectional dimension is <1 km, and the cases observed have a duration of ~10–30 s. The uniform coloration of all STEVE green features in these events suggests a common optical spectrum dominated by the oxygen 557.7-nm emission line. The source is most likely direct excitation of ambient oxygen by superthermal electrons generated by ionospheric turbulence induced by the extreme electric fields driving STEVE. Some conjectures about causal connections with overlying field-aligned structures are presented, based on coupling of thermal and gradient-drift instabilities, with analogues to similar dynamics observed from chemical release and ionospheric heating experiments.

The main ionospheric trough (MIT) is a salient density feature in the mid-latitude ionosphere and characterizing its structure is important for understanding GPS and HF signal propagation, and identifying geospace phenomena such as the plasmapause boundary layer. While a number of previous studies have statistically investigated the properties of the MIT utilizing low-altitude satellite observations, they have been limited to latitudinal cross sections, and have not considered the inherent two-dimensional structure of the trough. In this work, we develop a regularized inversion method for identifying the two dimensional structure of the trough in Total Electron Content (TEC) maps. Because no ground truth labels exist for the MIT, we extensively characterize the behavior of the algorithm by comparing it to the method developed by \citeA{aa-2020}. We show that statistics computed on the resulting labels are robust to our choice of algorithm parameters and that we are able to match the results of \citeA{aa-2020} with a particular selection of the parameters. Without ground truth, these two properties provide much stronger verification than a comparison using a single parameter setting. In addition to enabling fundamentally different studies, our MIT labels are able to provide statistical MIT properties with higher resolution.

This study exploits the volumetric sampling capabilities of the Resolute Bay Incoherent Scatter Radar (RISR-N) in collaboration with all-sky imagery and in-situ measurements (DMSP) to examine the interplay between cold plasma transport and auroral precipitation during a high-latitude lobe reconnection event on the dawn side. The IMF had an impulsive negative excursion in B$_z$ embedded within a prolonged period of B$_z>0$ and B$_y<0$. The combined effects of transport and magnetic stress release associated with a reconnection pulse resulted in a co-mingling of plasma patches and soft electron precipitation, creating regions of elevated electron density and temperature. Altitude profiles of ionospheric parameters extracted in the rest frame of the drifting patch showed an increase in $T_e$ above 200 km and $N_e$ below 250 km (both hallmarks of soft precipitation), while also showing small and predictable changes in $N_e$ near the F-region peak over the 34-minute duration of the event. For the first time, we identified that the simultaneous appearance of elevated $T_e$ and elevated F-region $N_e$ (i.e., a ‘hot patch’), thus providing a new formation process for hot patches. The physics-based GEMINI model was used to explore the response to the observed precipitation as a function of altitude and time. Enhancements in $N_e$ in the topside ionosphere (e.g., DMSP altitudes) are caused by upward ambipolar diffusion induced by ionospheric heating and not impact ionization. The study highlights the importance of densely distributed measurements in space and time for understanding both mesoscale and small-scale ionospheric dynamics in regions subject to complex forcing.