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Introduction: Magnetopause reconnection is known to impact the dayside ionosphere by driving fast ionospheric flows, auroral transients, and high-density plasma structures named polar cap patches. However, most of the observed reconnection impact is limited to one hemisphere, and a question arises as to how symmetric the impact is between hemispheres. Methods: We address the question using interhemispheric observations of poleward moving radar auroral forms (PMRAFs), which are a “fossil” signature of magnetopause reconnection, during a geomagnetic storm. We are particularly interested in the temporal repetition and spatial structure of PMRAFs, which are directly affected by the temporal and spatial variation of magnetopause reconnection. PMRAFs are detected and traced using SuperDARN complemented by DMSP, Swarm, and GPS TEC measurements. Results: The results show that PMRAFs occurred repetitively on time scales of about 10 min. They were one-to-one related to pulsed ionospheric flows, and were collocated with polar cap patches embedded in a Tongue of Ionization. The temporal repetition of PMRAFs exhibited a remarkably high degree of correlation between hemispheres, indicating that PMRAFs were produced at a similar rate, or even in close synchronization, in the two hemispheres. However, the spatial structure exhibited significant hemispherical asymmetry. In the Northern Hemisphere, PMRAFs/patches had a dawn-dusk elongated cigar shape that extended >1,000 km, at times reaching >2,000 km, whereas in the Southern Hemisphere, PMRAFs/patches were 2–3 times shorter. Conclusion: The interesting symmetry and asymmetry of PMRAFs suggests that both magnetopause reconnection and local ionospheric conditions play important roles in determining the degree of symmetry of PMRAFs/patches. 

Dynamic mesoscale flow structures move across the open field line regions of the polar caps and then enter the nightside plasma sheet where they can cause important space weather disturbances, such as streamers, substorms, and omega bands. The polar cap structures have long durations (apparently at least ∼1½ to 2 h), but their connections to disturbances have received little attention. Hence, it will be important to uncover what causes these flow enhancement channels, how they map to the magnetospheric and magnetosheath structures, and what controls their propagation across the polar cap and their dynamic effects after reaching the nightside auroral oval. The examples presented here use 630-nm auroral and radar observations and indicate that the motion of flow channels could be critical for determining when and where a particular disturbance within the nightside auroral oval will be triggered, and this could be included for full understanding of flow channel connections to disturbances. Also, it is important to determine how polar cap flow channels lead to flow channels within the auroral oval, i.e., the plasma sheet, and determine the conditions along nightside oval/plasma sheet field lines that interact with an incoming polar cap flow channel to cause a particular disturbance. It will also be interesting to consider the generality of geomagnetic disturbances being related to connections with incoming polar cap flow channels, including the location, time, and type of disturbances, and whether the duration and expansion of disturbances are related to flow channel duration and to multiple flow channels. 

Flow bursts are a major component of transport within the plasma sheet and auroral oval (where they are referred to as flow channels), and lead to a variety of geomagnetic disturbances as they approach the inner plasma sheet (equatorward portion of the auroral oval). However, their two-dimensional structure as they approach the inner plasma sheet has received only limited attention. We have examined this structure using both the Rice Convection Model (RCM) and ground-based radar and all sky imager observations. As a result of the energy dependent magnetic drift, the low entropy plasma of a flow burst spreads azimuthally within the inner plasma sheet yielding specific predictions of subauroral polarization stream (SAPS) and dawnside auroral polarization stream (DAPS) enhancements that are related to the field-aligned currents associated with the flow channel. Flow channels approximately centered between the dawn and dusk large-scale convection cells are predicted to give significant enhancements of both SAPS and DAPS, whereas flow channel further toward the dusk (dawn) convection cell show a far more significant enhancement of SAPS (DAPS) than for DAPS (SAPS). We present observations for cases having good coverage of flow channels as they approach the equatorward portion of the auroral oval and find very good qualitative agreement with the above RCM predictions, including the predicted differences with respect to flow burst location. Despite there being an infinite variety of flow channels’ plasma parameters and of background plasma sheet and auroral oval conditions, the observations show the general trends predicted by the RCM simulations with the idealized parameters. This supports that RCM predictions of the azimuthal spread of a low-entropy plasma sheet plasma and its associated FAC and flow responses give a realistic physical description of the structure of plasma sheet flow bursts (auroral oval flow channels) as they reach the inner plasma sheet (near the equatorward edge of the auroral oval). 

We report the first observations of the association between equatorward extending streamers and overshielding using the THEMIS all‐sky imagers and ground magnetometers. Because auroral streamers indicate plasma sheet flow bursts, these observations uncover the effect of flow bursts on overshielding. Results show that, in general, bright equatorward extended streamers were associated with an increase in equatorial electrojet (EEJ) on the nightside and a decrease in the dayside EEJ, indicating a striking correspondence between auroral streamers and overshielding conditions. Thus, the driving of overshielding at equatorial latitudes can be identified via bright equatorward extended streamers, indicating that flow bursts are an alternate means to discern the earthward injections that increase the region 2 field aligned currents and associated overshielding electric fields. Repetitive auroral streamers were associated with repetitive overshielding, resulting in a stepwise development of the dayside and nightside EEJ. The stepwise intensifications were also observed in the midlatitude positive bay and Pi2 pulsations. Our results could explain the occurrence of overshielding conditions at equatorial latitudes during substorms and nonsubstorm times without a northward turning of IMF‐Bz. As seen through streamers, the localized current structures (wedgelets) associated with flow bursts giving injection that leads to overshielding is titled northeast‐to‐southwest. Our results add a new element to the understanding of high‐to‐low latitude electrodynamical coupling by demonstrating the association between bright equatorward extended auroral streamers and enhanced shielding electric fields caused by earthward injections associated with flow bursts.

 

A new observational phenomenon, named Simultaneous Global Ionospheric Density Disturbance (SGD), is identified in GNSS total electron content (TEC) data during periods of three typical geospace disturbances: a Coronal Mass Ejection‐driven severe disturbance event, a high‐speed stream event, and a minor disturbance day with a maximum Kp of 4. SGDs occur frequently on dayside and dawn sectors, with a ∼1% TEC increase. Notably, SGDs can occur under minor solar‐geomagnetic disturbances. SGDs are likely caused by penetration electric fields (PEFs) of solar‐geomagnetic origin, as they are associated with Bz southward, increased auroral AL/AU, and solar wind pressure enhancements. These findings offer new insights into the nature of PEFs and their ionospheric impact while confirming some key earlier results obtained through alternative methods. Importantly, the accessibility of extensive GNSS networks, with at least 6,000 globally distributed receivers for ionospheric research, means that rich PEF information can be acquired, offering researchers numerous opportunities to investigate geospace electrodynamics.

 

We use simultaneous auroral imaging, radar flows, and total electron content (TEC) measurements over Alaska to examine whether there is a direct connection of large-scale traveling ionospheric disturbances (LSTIDs) to auroral streamers and associated flow channels having significant ground magnetic decreases. Observations from seven nights with clearly observable flow channels and/or auroral streamers were selected for analysis. Auroral observations allow identification of streamers, and TEC observations detect ionization enhancements associated with streamer electron precipitation. Radar observations allow direct detection of flow channels. The TEC observations show direct connection of streamers to TIDs propagating equatorward from the equatorward boundary of the auroral oval. The TIDs are also distinguished from the streamers to which they connect by their wave-like TEC fluctuations moving more slowly equatorward than the TEC enhancements from streamer electron precipitation. TIDs previously observed propagating equatorward from the auroral oval have been identified as LSTIDs. Thus, the TIDs here are likely LSTIDs, but we lack sufficient TEC coverage necessary to demonstrate that they are indeed large scale. Furthermore, each of our events shows TID’s connection to groups of a few streamers and flow channels over a period in the order of 15 min and a longitude range of ∼15–20°, and not to single streamers. (Groups of streamers are common during substorms. However, it is not currently known if streamers and associated flow channels typically occur in such groups.) We also find evidence that a flow channel must lead to a sufficiently large ionospheric current for it to lead to a detectable LSTID, with a few tens of nT ground magnetic field decreases not being sufficient. 

Recent attention has been given to mesoscale phenomena across geospace (∼10 s km to 500 km in the ionosphere or ∼0.5 R E to several R E in the magnetosphere), as their contributions to the system global response are important yet remain uncharacterized mostly due to limitations in data resolution and coverage as well as in computational power. As data and models improve, it becomes increasingly valuable to advance understanding of the role of mesoscale phenomena contributions—specifically, in magnetosphere-ionosphere coupling. This paper describes a new method that utilizes the 2D array of Time History of Events and Macroscale Interactions during Substorms (THEMIS) white-light all-sky-imagers (ASI), in conjunction with meridian scanning photometers, to estimate the auroral scale sizes of intense precipitating energy fluxes and the associated Hall conductances. As an example of the technique, we investigated the role of precipitated energy flux and average energy on mesoscales as contrasted to large-scales for two back-to-back substorms, finding that mesoscale aurora contributes up to ∼80% (∼60%) of the total energy flux immediately after onset during the early expansion phase of the first (second) substorm, and continues to contribute ∼30–55% throughout the remainder of the substorm. The average energy estimated from the ASI mosaic field of view also peaked during the initial expansion phase. Using the measured energy flux and tables produced from the Boltzmann Three Constituent (B3C) auroral transport code (Strickland et al., 1976; 1993), we also estimated the 2D Hall conductance and compared it to Poker Flat Incoherent Scatter Radar conductance values, finding good agreement for both discrete and diffuse aurora.