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Abstract Electron density irregularities in the ionosphere can give rise to scintillations, affecting radio wave phase and amplitude. While scintillations in the cusp and polar cap regions are commonly associated with mesoscale density inhomogeneities and/or shearing, the auroral regions exhibit a strong correlation between scintillation and density structures generated by electron precipitation (arcs). We aim to examine the impact of electron precipitation on the formation of scintillation‐producing density structures using a high‐resolution physics‐based plasma model, the “Geospace Environment Model of Ion‐Neutral Interactions,” coupled with a radio propagation model, the “Satellite‐beacon Ionospheric‐scintillation Global Model of the upper Atmosphere.” Specifically, we explore the effects of varying spatial and temporal characteristics of the precipitation, including electron total energy flux and their characteristic energies, obtained from the all‐sky‐imagers and Poker Flat Incoherent Scatter Radar observations, on auroral scintillation. To capture small‐scale structures, we incorporate a power‐law turbulence spectrum that induces short wavelength features sensitive to scintillation. Finally, we compare our simulated scintillation results with satellite‐observed scintillations, along with spectral comparisons. 

Abstract 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 (>4 km/s), high temperatures (>4,000 K), and very large current density drivers (up to 1 μA/m²). 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. 

Abstract An approach for creating continental‐scale, multi‐scale plasma convection maps in the nightside high‐latitude ionosphere using the spherical elementary current systems technique has been developed and evaluated. The capability to reconstruct meso‐scale flow channels improved dramatically, and the velocity errors were reduced by ∼30% compared to the spherical harmonic fitting method. Uncertainties of velocity vectors estimated by varying the model setup was also low. Convection maps for a substorm event revealed multiple flow channels in the polar cap, dominating the convection in the quiet time and early growth phase. The meso‐scale flows extended toward the nightside auroral oval and had continuous flow channels over >20° of latitude, and the flow channels dynamically merged and bifurcated. The substorm onset occurred along one of the flow channels, and the azimuthal extent of the enhanced flows coincided with the initial width of the auroral breakup. During the expansion phase, the meso‐scale flows repetitively crossed the oval poleward boundary, and some of them contributed to subauroral polarization streams enhancements. Increased flows extended duskward, along with the westward traveling surge. Then, flows near midnight weakened and evolved to the Harang flow shear. The meso‐scale flow channels had significant (∼10%–40% on average) contributions to the total plasma transport. The meso‐scale flows were highly variable on ∼10 min time scales and their individual maximum contributions reached upto 73%. These results demonstrate the capability of specifying realistic convection patterns, quantifying the contribution of meso‐scale transport, and evaluating the relationship between meso‐scale flows and localized auroral forms. 

Abstract Dipolarizing flux bundles (DFBs) have been suggested to transport energy and momentum from regions of reconnection in the magnetotail to the high latitude ionosphere, where they can generate localized ionospheric currents that can produce large nighttime geomagnetic disturbances (GMDs). In this study we identified DFBs observed in the midnight sector from ∼7 to ∼10 R_Eby THEMIS A, D, and E during days in 2015–2017 whose northern hemisphere magnetic footpoints mapped to regions near Hudson Bay, Canada, and have compared them to isolated GMDs observed by ground magnetometers. We found 6 days during which one or more of these DFBs coincided to within ±3 min with ≥6 nT/s GMDs observed by latitudinally closely spaced ground‐based magnetometers located near those footpoints. Spherical elementary current systems (SECS) maps and all‐sky imager data provided further characterization of two events, showing short‐lived localized intense upward currents, auroral intensifications and/or streamers, and vortical perturbations of a westward electrojet. On all but one of these days the coincident DFB—GMD pairs occurred during intervals of high‐speed solar wind streams but low values of SYM/H. The observations reported here indicate that isolated DFBs generated under these conditions influence only limited spatial regions nearer Earth. In some events, in which the DFBs were observed closer to Earth and with lower Earthward velocities, the GMDs occurred slightly earlier than the DFBs, suggesting that braking had begun before the time of the DFB observation. 

Abstract We utilized a 4K imaging to examine properties of fine‐scale structures of Strong Thermal Emission Velocity Enhancement (STEVE) near the magnetic zenith. Its high spatial (0.09 km at 200 km altitude) and temporal (24 Hz) resolution provided unprecedented details of fine‐scale structures in the subauroral ionosphere. Although the STEVE emission was seen as a homogeneous purple/mauve arc in the all‐sky images, the high‐speed imaging revealed that STEVE contained substantial multi‐scale structures. The characteristic wavelength and period were 12.4 ± 7.4 km and 1.4 ± 0.8 s, and they drifted westward at 8.9 ± 0.7 km/s. The speed is comparable to the reported magnitude of the intense subauroral ion drifts (SAID), suggesting that the fine‐scale structures are an optical manifestation of theE × Bdrift in the intense SAID. A spectral analysis identified multiple peaks at >10, 4, 2, 1.1, and <1/5 s period (>83, 33, 16, 9, and <1.7 km wavelength). Although most of the fine‐scale structures were stable during the drift across the field of view, some of the structures dynamically evolved within a few tens of km. The fine‐scale structures have a power law spectrum with a slope of −1, indicating that shear flow turbulence cascade structures to smaller scales. The fine‐scale structures pose a challenge to the subauroral ionosphere‐thermosphere interaction about how the ionosphere creates such fine‐scale structures and how the thermosphere reacts much faster than expected from a typical chemical reaction time. 

Abstract We present observations during two substorms using simultaneous Time History of Events and Macroscale Interactions During Substorms satellites and all‐sky imagers to determine plasma sheet dynamics associated with substorm auroral onset beads. The multi‐satellite observations showed that the cross‐tail current decreased and the field‐aligned currents increased at the substorm auroral onset, indicating that the satellites detected an initiation of the currents being deflected to the ionosphere. For duskward‐propagating beads, the electric field was tailward, and ions were accumulated closer to the Earth than electrons. The mapped bead propagation speed was close to energetic ion drift speed. Theand electron drift speeds increased duskward and reduced the cross‐tail current at the onset. For dawnward‐propagating beads, the electric field was equatorward/earthward, and electrons were inferred to accumulate earthward of ions. The mapped bead propagation speed was comparable to the dawnwardand electron drift speeds. The duskward ion drift and tail current were reduced, and electrons became the dominant current carrier. We suggest that the plasma species that is responsible for the bead propagation changes with the electric field configuration and that the tail current reduction by the enhanceddrift at onset destabilizes the plasma sheet. Ion and electron outflows substantially increased low‐energy plasma density and may have increased the role ofdrifts. The bead wavelength was comparable to ion gyroradius and thus ion kinetic effects are important for determining the wavelength. In the dawnward‐propagating event, the mode of oscillation in the plasma sheet was suggested to be the sausage‐mode flapping oscillations. 

Abstract Inner‐magnetospheric conditions for subauroral polarization streams (SAPS) and subauroral ion drifts (SAID) have been investigated statistically using Time History of Events and Macroscale Interactions during Substorms and RBSP observations. We found that plasma sheet electron fluxes at its earthward edge are larger for SAID than SAPS. The ring current ion flux for SAID formed a local maximum near SAID, but the ion flux for SAID was not necessarily larger than for SAPS. The median potential drop across SAID and SAPS is nearly the same, but the potential drop for intense SAID is substantially larger than that for SAPS. The plasmapause is sharper and electromagnetic waves were more intense for SAID. The SAID velocity peak does not strongly correlate with solar wind or geomagnetic indices. These results indicate that local plasma structures are more important for SAPS/SAID velocity characteristics as compared to global magnetospheric conditions. 

Abstract Pc5 ultralow frequency waves are important for transferring energy between the magnetosphere and ionosphere. While many observations have been performed on Pc5 waves properties, it has been difficult to determine the source region, signal propagation path, and the two‐dimensional structure of Pc5 waves beyond coverage by a small number of satellites. Pc5 waves often show a dawn‐dusk asymmetry, but the cause of the asymmetry is under debate. To address these issues, we used conjunction events between the THEMIS satellites and all‐sky imagers and analyzed two Pc5 wave events that were stronger on the dawnside. For both events, the Pc5 waves propagated from dawnside magnetopause toward the nightside magnetosphere. The Pc5 waves were also associated with dawnside magnetopause surface waves, which were probably induced by the Kelvin‐Helmholtz instability. The ionospheric equivalent currents identified multiple vortices on the dawnside associated with quasi‐periodic auroral arcs and much weaker perturbations on the duskside. Global auroral imaging also presented a similar dawn‐dusk asymmetry with multiple arcs on the dawnside, while only one or two major arcs existed on the duskside. Pc5 waves in the magnetosphere had an anti‐phase relation between the total magnetic field and thermal pressure, with a slower propagation velocity compared with magnetohydrodynamic waves. The Poynting flux was anti‐sunward with an oscillating field‐aligned component. These properties suggest that Pc5 waves were slow or drift mirror mode waves coupled with standing Alfven waves. The ground‐based and multi‐satellite observations provide crucial information for determining the Pc5 waves properties, possible source region, and signal propagation path. 

Abstract During the 17 March 2015 geomagnetic storm, citizen scientist observations from Dunedin (45.95°S, 170.32°E), New Zealand, revealed a bright wide red arc known as stable auroral red (SAR) arc evolving into a thin white‐mauve arc, known as Strong Thermal Emission Velocity Enhancement (STEVE). An all‐sky imager at the Mount John Observatory (43.99°S, 170.46°E), 200 km north of Dunedin, detected an extremely bright arc in 630.0 nm, with a peak of ∼6 kR, colocated with the arc measured at Dunedin at an assumed height of 425 km. Swarm satellite data measured plasma parameters that showed strong subauroral ion drift signatures when the SAR arc was observed. These conditions intensified to extremely high values in a thinner channel when STEVE was present. Our results highlight the fast evolution of plasma properties and their effects on optical emissions. Current theories and models are unable to reproduce or explain these observations. 

Abstract We utilized citizen scientist photographs of subauroral emissions in the upper atmosphere and identified a repeatable sequence of proton aurora and subauroral red (SAR) arc during substorms. The sequence started with a pair of green diffuse emissions and a red arc that drifted equatorward during the substorm expansion phase. Simultaneous spectrograph and satellite observations showed that they were subauroral proton aurora, where ion precipitation created secondary electrons that illuminated aurora in green and red colors. The ray structures in the red arc also indicated existence of low‐energy electron precipitation. The green diffuse aurora then decayed but the red arc (SAR arc) continued to move equatorward during the substorm recovery phase. This sequence suggests that the SAR arc was first generated by secondary electrons associated with ion precipitation and may then transition to heat flux or Joule heating. Proton aurora provides observational evidence that ion injection to the inner magnetosphere is the energy source for the initiation of the SAR arc.