Subauroral Polarization Streams Research Articles

Dynamics of Auroral Precipitation Boundaries Associated With STEVE and SAID

AbstractUsing Defense Meteorological Satellite Program (DMSP) and National Oceanic and Atmospheric Administration (NOAA) satellite observations and ground‐based observations by the THEMIS all‐sky imagers (ASIs) and SuperDARN radars, we determine how the equatorward boundary locations of ring current ions and plasma sheet electrons at pre‐midnight relate to occurrence of strong thermal emission velocity enhancement (STEVE) and intense subauroral ion drifts (SAID) during substorms. We found that the STEVE events are associated with a sharper gradient of electron precipitating flux, lower precipitating ion flux, and a narrower (<1°) latitudinal gap between the equatorward boundaries of trapped ring current ions and precipitating plasma sheet electrons and narrower region‐2 field‐aligned currents (FACs) than for the non‐STEVE events. The narrow gap of the particle boundaries contains intense SAID, higher upflow velocity, lower trough density, and slightly higher electron temperature than those for the non‐STEVE events. The non‐STEVE substorms have much wider gaps between the trapped ions and precipitating electrons, and subauroral polarization streams (SAPS) do not show intense SAID. These results indicate that subauroral flows and downward FACs for the STEVE events can only flow within the latitudinally narrow subauroral low‐conductance region between the ion and electron boundaries, resulting in intense SAID and heating. During the non‐STEVE events, the SAPS flows can flow in the latitudinally wide region without forming intense SAID.

Magnetospheric Conditions for STEVE and SAID: Particle Injection, Substorm Surge, and Field‐Aligned Currents

AbstractTo understand magnetosphere‐ionosphere conditions that result in thermal emission velocity enhancement (STEVE) and subauroral ion drifts (SAID) during the substorm recovery phase, we present substorm aurora, particle injection, and current systems during two STEVE events. Those events are compared to substorm events with similar strength but without STEVE. We found that the substorm surge and intense upward currents for the events with STEVE reach the dusk, while those for the non‐STEVE substorms are localized around midnight. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observations show that location of particle injection and fast plasma sheet flows for the STEVE events also shifts duskward. Electron injection is stronger and ion injection is weaker for the STEVE events compared to the non‐STEVE events. SAID are measured by Super Dual Auroral Radar Network during the STEVE events, but the non‐STEVE events only showed latitudinally wide subauroral polarization streams without SAID. To interpret the observations, Rice Convection Model (RCM) simulations with injection at premidnight and midnight have been conducted. The simulations successfully explain the stronger electron injection, weaker ion injection, and formation of SAID for injection at premidnight, because injected electrons reach the premidnight inner magnetosphere and form a narrower separation between the ion and electron inner boundaries. We suggest that substorms and particle injections extending far duskward away from midnight offer a condition for creating STEVE and SAID due to stronger electron injection to premidnight. The THEMIS all‐sky imager network identified the east‐west length of the STEVE arc to be ~1900 km (~2.5 h magnetic local time) and the duration to be 1–1.5 h.

Dawnside Auroral Polarization Streams

AbstractAlthough the postmidnight‐to‐dawn sector of the auroral ionosphere contains interesting dynamic phenomena that may significantly impact the magnetosphere‐ionosphere‐thermosphere system, it has been much less studied than the dusk‐to‐premidnight sector. We discuss a dynamic phenomenon in the postmidnight‐to‐dawn sector of the auroral oval, eastward fast flows mainly within the expanse of the Region 1 current (its part equatorward of the polar cap). These flows peak and have a steep speed gradient (increase from low to high latitude) near the interface between the Region 1 and Region 2 currents. Because such flows correspond to an electric field that most likely comes from enhanced Region 2 currents and an associated spatial conductivity gradient, their generation mechanism is analogous to that of a subauroral polarization stream. Therefore, we refer to such an eastward flow as a dawnside auroral polarization stream (DAPS). We show several examples of the presence and absence of DAPS under different geomagnetic activity levels. A DAPS' electric field can heat the ionosphere (and thus the thermosphere), change the convection pattern of the magnetosphere‐ionosphere system, and modify the drift path of magnetospheric particles. Because a DAPS' flow peak maps to a major site of magnetic‐kinetic energy conversion in the magnetosphere (the transition region between dipole and stretched field), it may be important for the conversion. A DAPS' steep flow gradient is also potentially important; it may lead to instabilities, such as that responsible for auroral Omega bands. Given its potential importance, knowledge of DAPS is fundamental for understanding the magnetosphere‐ionosphere‐thermosphere system.

Geomagnetic Storm‐Induced Plasma Density Enhancements in the Southern Polar Ionospheric Region: A Comparative Study Using St. Patrick's Day Storms of 2013 and 2015

AbstractThe occurrence of St. Patrick's Day (17 March) geomagnetic storms during two different years (2013 and 2015) with similar solar flux levels but varying storm intensity provided an opportunity to compare and contrast the responses of the ionosphere‐thermosphere (IT) system to different levels of geomagnetic activity. The evolution of positive ionospheric storms at the southern polar stations Bharati (76.6°S MLAT) and Davis (76.2°S MLAT) and its causative connection to the solar wind driving mechanisms during these storms has been investigated in this paper. During the main phase of both the storms, significant enhancements in TEC and phase scintillation were observed in the magnetic noon/ midnight period at Bharati and Davis. The TEC in the midnight sector on 17 March 2015 was significantly higher compared to that on 17 March 2013, in line with the storm intensity. The TEC enhancements during both the storm events are associated with the formation of the storm‐enhanced densities (SEDs)/tongue of ionization (TOI). The strong and sustained magnetopause erosion led to the prevalence of stronger storm time electric fields (prompt penetration electric field (PPEF)/subauroral polarization streams (SAPS)) for long duration on 17 March 2015. This combined with the action of neutral winds at midlatitudes favored the formation of higher plasma densities in the regions of SED formation on this day. The same was weaker during the 17 March 2013 storm due to the fast fluctuating nature of interplanetary magnetic field (IMF) Bz. This study shows that the duration and extent of magnetopause erosion play an important role in the spatiotemporal evolution of the plasma density distribution in the high‐midlatitude ionosphere.

Statistical Study of Ion Upflow Associated with Subauroral Polarization Streams (SAPS) at Substorm Time

AbstractWe present a statistical study of the ion upflow associated with subauroral polarization streams (SAPS) in the ionospheric subauroral region at different substorm times using three Defense Meteorological Satellite Program satellite (F16–F18) data for five years (2010–2014) in the Northern Hemisphere. The results show similarities between SAPS and the ion upflow at different intensity of substorms both in occurrence rate distribution and velocity distribution. In comparison to SAPS, the distribution of the ion upflow shows the smaller occurrence region and lower velocity. We also find that frictional heating plays an important role in ion upflow from the SAPS region. The intense substorms can trigger strong SAPS channels, enhanced frictional heating, and large ion upflow. In addition, there is a moderate linear correlation between SAPS velocity and field‐aligned velocity that is consistent with some previous findings. Our results also show that frictional heating can gradually dominate the ion upflow process in intense substorms, while it may not be the only factor to affect the whole upflow process.

Investigating Magnetosphere‐Ionosphere‐Thermosphere (M‐I‐T) Coupling Occurring During the 7–8 November 2004 Superstorm

AbstractIn this study, we investigate the shock‐sheath driven 7–8 November 2004 superstorm for its flux transfer events and resultant flow channel (FC) events and associated neutral (DN) and electron (Ne) density features in order to understand better the underlying coupled magnetosphere (M) and ionosphere (I) processes and responses in the thermosphere (T). We focus on the (i) subauroral, auroral, and polar cap regions, (ii) localized DN increases and associated Ne features and FCs developed, and (iii) energy deposition occurred. Results show the development of localized DN increases (1) within/over FCs and associated enhanced small‐scale field aligned currents suggesting Joule heating driving upwelling during forward and reverse polar convections, (2) appearing with Ne increases during storm‐enhanced density (SED) events suggesting strong M‐I‐T coupling and with Ne depletions during plasmaspheric erosion events suggesting weak M‐I‐T coupling, and (3) in the thermosphere's increasing NO and continuously low O/N2 composition regions. During erosion events, strong storm‐time subauroral polarization streams (SAPS) E fields developed. Meanwhile the well‐developed plasmapause appeared with decreased total electron content (TEC) on its poleward side and with increased TEC and Ne (appearing as a shoulder feature that is the signature of SED) on its equatorward side. From these we conclude that although strong M‐I‐T coupling was apparent during SED events, M‐I‐T coupling was also strong during erosion events when the combination of strong convection E field and large storm‐time SAPS E fields eroded the high‐latitude region and thus decreased the high‐latitude Ne and TEC.

When Plasma Streams Tie up Equatorial Plasma Irregularities with Auroral Ones

AbstractWe present a new pattern of storm‐induced ionospheric irregularities behavior at midlatitudes—poleward‐streaming plasma density depletions. Under disturbed conditions, they appear at North America low latitudes as a part of extended postsunset equatorial plasma bubbles, and further, they are streaming from low latitudes in a northwestward, poleward direction toward the main ionospheric trough and auroral irregularities zone. The poleward‐streaming plasma depletions represent a new phenomenon with the similar northwestward transportation path across the continental United States as storm‐enhanced density (SED) plumes. The channels of poleward‐streaming plasma depletions were stretched from low‐latitude base toward higher latitudes—they are found to occur for geomagnetic storms under specific combination of steady southward interplanetary magnetic field, subauroral polarization streams (SAPS) electric fields, and enhanced westward drifts at midlatitudes, resulting in northwestward plasma transportation equatorward of the SAPS region. The poleward‐streaming plasma depletions form an illusion of traveling ionospheric disturbances (TIDs) moving in a poleward, northwestward direction—this propagation direction is opposite to typical equatorward propagation of storm‐induced large‐scale TIDs generated in the auroral zone and propagated toward the equator. This phenomenon is accompanied by strong ionospheric irregularities that occurred over both edges of plasma depletion channel at midlatitudes. For two comparable geomagnetic storms, these poleward‐streaming plasma depletions persisted for several hours, posing a localized threat for GPS‐based positioning applications. Even moderate‐to‐intense storms (Dst minimum−145 nT) can promote such effects at midlatitudes.

Bifurcated Region 2 Field‐Aligned Currents Associated With Substorms

AbstractWe analyze the magnetosphere‐ionosphere field‐aligned currents associated with substorms using the Active Magnetosphere and Planetary Electrodynamics Response Experiment. We report a new phenomenon related to substorm onset: the development of a second pair of R2 field‐aligned currents located equatorward of the preexisting R1/R2 currents, especially in the dusk sector. The appearance of such events favors the summer hemisphere, suggesting that ionospheric conductance modulates this phenomenon. During ongoing geomagnetic activity, the events have a quasiperiodicity of approximately 1 hr. We suggest that this phenomenon is related to subauroral polarization streams, which are strong westward flows in the dusk sector midlatitude ionosphere. This paper proposes a new mechanism that describes the formation of these current bifurcations: Consecutive particle injections into the inner magnetosphere during disturbed geomagnetic conditions cause separate partial ring currents to form, leading to the presence of distinct R2 current systems, all flowing into the R1 current.

НАБЛЮДЕНИЕ БЫСТРЫХ СУБАВРОРАЛЬНЫХ ДРЕЙФОВ ИОНОСФЕРНОЙ ПЛАЗМЫ ПО ДАННЫМ ЯКУТСКОЙ МЕРИДИОНАЛЬНОЙ ЦЕПОЧКИ СТАНЦИЙ

Using long-term data from Yakut meridional chain of Yakutsk — Zhigansk — Batagay — Tixie ionospheric stations, we study ionospheric signatures of fast subauroral ion drift. Sharp drops or “falls” of critical frequencies (FCF) of the ionospheric F layer are shown to be one of the main signatures of the development of fast subauroral ion drifts near or at the zenith of the observation station. Comparison between long-term ground-based and satellite measurements indicates that there is good agreement between seasonal variation in the probability of occurrence of FCF derived from ground-based data and subauroral ion drifts derived from DMSP satellite data. Such a coincidence implies that both satellite and ground-based measurement methods register the same phenomenon in the boundary layers of the plasmasphere, namely, the appearance and development of electric fields of magnetospheric origin. The local time for recording of falls of the critical frequency derived from the ground-based data is shown to closely coincide with the appearance time of subauroral polarization streams of plasma according to satellite data. We can therefore conclude that most of the observed FCFs derived from ground-based data refer to intense storms.

FAST SUBAURORAL DRIFTS OF IONOSPHERE PLASMA ACCORDING TO DATA FROM YAKUT MERIDIONAL CHAIN OF STATIONS

Using long-term data from Yakut meridional chain of Yakutsk — Zhigansk — Batagay — Tixie ionospheric stations, we study ionospheric signatures of fast subauroral ion drift. Sharp drops or “falls” of critical frequencies (FCF) of the ionospheric F layer are shown to be one of the main signatures of the development of fast subauroral ion drifts near or at the zenith of the observation station. Comparison between long-term ground-based and satellite measurements indicates that there is good agreement between seasonal variation in the probability of occurrence of FCF derived from ground-based data and subauroral ion drifts derived from DMSP satellite data. Such a coincidence implies that both satellite and ground-based measurement methods register the same phenomenon in the boundary layers of the plasmasphere, namely, the appearance and development of electric fields of magnetospheric origin. The local time for recording of falls of the critical frequency derived from the ground-based data is shown to closely coincide with the appearance time of subauroral polarization streams of plasma according to satellite data. We can therefore conclude that most of the observed FCFs derived from ground-based data refer to intense storms.

Dependence of the Equatorial Electrojet on Auroral Activity and In Situ Solar Insulation

AbstractBy using 10 years of Challenging Minisatellite Payload satellite observations, we investigate the average conditions of the interplanetary magnetic field (IMF) prevailing during the westward counter equatorial electrojet (CEJ). Equally, we compared the average IMF conditions accompanying high‐latitude field‐aligned currents of the Region 1 (R1) and Region 2 (R2). It shows that both CEJ and high‐latitude field‐aligned currents events when R2 is greater than R1 tend to happen preferably during the northward turning of the IMF Bz and the substorm recovery phase. Sunlight has an important influence on the longitudinal distribution of the equatorial electrojet (EEJ), and the effect is opposite to the tidal electric field at region. The anticorrelation between cos (SZA) (solar zenith angle effect) average values during CEJ events and EEJ intensity is most prominent around June solstice. By using combined measurements from Challenging Minisatellite Payload and DMSP satellites, it is found that before the occurrence and in the initial phase of a subauroral polarization stream the EEJ gets enhanced, and after about 30 min it reduces in intensity. The CEJ occurrence rate more than doubles during subauroral polarization stream periods compared to normal conditions.

Subauroral and Polar Traveling Ionospheric Disturbances During the 7–9 September 2017 Storms

AbstractThis study provides new scenarios for storm time traveling ionospheric disturbance excitation and subsequent propagation at subauroral and polar latitudes. We used ground‐based total electron content observations from Global Navigation Satellite System receivers combined with wide field, subauroral ionospheric plasma parameters measured with the Millstone Hill Incoherent Scatter Radar during strong September 2017 geospace storms. Observations provide the first evidence of significant influences on traveling ionospheric disturbance (TID) propagation and excitation caused by the presence of large subauroral polarization stream flow channels. Simultaneous large‐ and medium‐scale TIDs evolved during the event in a broad subauroral and midlatitude area near dusk. Similar concurrent TIDs occurred near dawn sectors as well during a period of sustained southward Bz. Medium‐scale TIDs at subauroral and midlatitudes had wave fronts aligned northwest‐southeast near dusk, and northeast‐southwest near dawn. These wave fronts were highly correlated with the direction of storm time large zonal plasma drift enhancements at these latitudes. At high latitudes, unexpected, predominant, and persistent storm time TIDs were identified with 2000+ km zonal wave fronts and 15% total electron content perturbation amplitudes, moving in transpolar propagation pathways from the dayside into the nightside. This propagation direction in the polar region was opposite to the normal assumption that TIDs originated in the nightside auroral region. Results suggest that significant dayside sources, such as cusp regions, can be efficient in generating transpolar TIDs during geospace storm intervals.

A Simulation of the Field‐Aligned Plasma Transport in the Plasmaspheric Plume During the 2015 St. Patrick's Day Storm

AbstractIn this paper, based on a calculated open E × B convection passage of a flux tube with subauroral polarization streams (SAPS) electric field involved, we use the Dynamic Fluid‐Kinetic model to simulate the transport of major ion species (H+, He+, and O+) along magnetic field line (field‐aligned) within the flux tube during the 2015 St. Patrick's Day storm. The drift trajectory is confirmed to be quite realistic based on observations and empirical models, meanwhile, the foot print of flux tube is initiated from subauroral latitudes toward polar latitudes along this drift pass. The Dynamic Fluid‐Kinetic simulation displays interesting temporal evolution of the field‐aligned plasma distribution at subauroral latitudes: The storm‐enhanced density region continuously provides upward ion flux filling into plasmasphere, but the equatorial mass loading in plasmaspheric plume increases at first and then decreases. Further analyses found that the SAPS particularly impact the field‐aligned transport of O+ particles from ionosphere to plasmasphere but have much less effect on H+ and He+ particles at subauroral latitudes, which causes significant enhancements of equatorial O+ density. The results show that the SAPS have significant effects on both drifting trajectory of the flux tube and associated field‐aligned ion dynamics. This work reveals intimate storm time interaction between the inner magnetosphere and ionosphere which may affect the dynamics in outer magnetosphere or even at magnetopause with flux tube convection.

Multi-point observations and modeling of subauroral polarization streams (SAPS) and double-peak subauroral ion drifts (DSAIDs): A case study

While subauroral polarization streams (SAPS) are well recognized as representatively one of the most important features of magnetosphere-ionosphere (M-I) coupling processes in the subauroral region, the double-peak subauroral ion drifts (DSAIDs) is a newly recognized ionospheric phenomenon, categorized as a subset of subauroral ion drifts (SAIDs). In this study, we investigate both SAPS and DSAIDs that appear during the storm main phase of the 17 March 2015 event through a combination of multi-point observations and numerical simulations. We find that when SAPS/DSAIDs are observed by the DMSP spacecraft near the dusk subauroral region, strong electric fields are detected minutes later by the Van Allen Probes almost in the same conjugate region near the equatorial plane. Numerical simulations are carried out not only to reveal the global context and dynamic evolution of the SAPS in both the magnetospheric and ionospheric systems, but also to aid the understanding of the effect of conductance on the DSAIDs. Our results confirm that SAPS are indeed associated with Region 2 field-aligned currents (FACs) flowing into the low conductance region. On the other hand, the DSAIDs may be related to the double-conductance-trough in the subauroral region.

Transport and Loss of Ring Current Electrons Inside Geosynchronous Orbit During the 17 March 2013 Storm.

Ring current electrons (1–100 keV) have received significant attention in recent decades, but many questions regarding their major transport and loss mechanisms remain open. In this study, we use the four‐dimensional Versatile Electron Radiation Belt code to model the enhancement of phase space density that occurred during the 17 March 2013 storm. Our model includes global convection, radial diffusion, and scattering into the Earth's atmosphere driven by whistler‐mode hiss and chorus waves. We study the sensitivity of the model to the boundary conditions, global electric field, the electric field associated with subauroral polarization streams, electron loss rates, and radial diffusion coefficients. The results of the code are almost insensitive to the model parameters above 4.5 R E R E, which indicates that the general dynamics of the electrons between 4.5 R E and the geostationary orbit can be explained by global convection. We found that the major discrepancies between the model and data can stem from the inaccurate electric field model and uncertainties in lifetimes. We show that additional mechanisms that are responsible for radial transport are required to explain the dynamics of ≥40‐keV electrons, and the inclusion of the radial diffusion rates that are typically assumed in radiation belt studies leads to a better agreement with the data. The overall effect of subauroral polarization streams on the electron phase space density profiles seems to be smaller than the uncertainties in other input parameters. This study is an initial step toward understanding the dynamics of these particles inside the geostationary orbit.

Merging of Storm Time Midlatitude Traveling Ionospheric Disturbances and Equatorial Plasma Bubbles

AbstractPostsunset midlatitude traveling ionospheric disturbances (TIDs) and equatorial plasma bubbles (EPBs) were simultaneously observed over American sector during the geomagnetic storm on 8 September 2017. The characteristics of TIDs are analyzed by using a combination of the Millstone Hill incoherent scatter radar data and 2‐D detrended total electron content (TEC) from ground‐based Global Navigation Satellite System receivers. The main results associated with EPBs are as follows: (1) stream‐like structures of TEC depletion occurred simultaneously at geomagnetically conjugate points, (2) poleward extension of the TEC irregularities/depletions along the magnetic field lines, (3) severe equatorial and midlatitude electron density (Ne) bite outs observed by Defense Meteorological Satellite Program and Swarm satellites, and (4) enhancements of ionosphere F layer virtual height and vertical drifts observed by equatorial ionosondes near the EPBs initiation region. The stream‐like TEC depletions reached 46° magnetic latitudes that map to an apex altitude of 6,800 km over the magnetic equator using International Geomagnetic Reference Field. The formation of this extended density depletion structure is suggested to be due to the merging between the altitudinal/latitudinal extension of EPBs driven by strong prompt penetration electric field and midlatitude TIDs. Moreover, the poleward portion of the depletion/irregularity drifted westward and reached the equatorward boundary of the ionospheric main trough. This westward drift occurred at the same time as the sudden expansion of the convection pattern and could be attributed to the strong returning westward flow near the subauroral polarization stream region. Other possible mechanisms for the westward tilt are also discussed.

Evolution of the Subauroral Polarization Stream Oscillations During the Severe Geomagnetic Storm on 20 November 2003

AbstractWe report multisatellite observations of the oscillations in the subauroral polarization stream (SAPS) during a severe magnetic storm on 20 November 2003. The SAPS oscillations (SAPSOs) occurred during the main phase of the magnetic storm when the y component of the southward interplanetary magnetic field (IMF BY) turned from positive to negative. The SAPSOs were first observed in the premidnight sector and propagated toward the dusk sector. The formation and evolution of SAPSO corresponded well with the plasma sheet ions injection and precipitation, indicating that the SAPSOs are possibly generated by the interaction between the hot plasma sheet and the cold plasmasphere under particular conditions (e.g., change of the polarity of IMF BY accompanied with a sudden enhancement of plasma sheet ion density). The hemispheric asymmetry of the SAPS channels is suggested to be related to the hemispheric differences in the ionospheric plasma condition and the ionospheric convection.

A New Empirical Model of the Subauroral Polarization Stream

AbstractRegions of persistent westward directed flows are often observed equatorward of the auroral oval in the dusk‐midnight sector. In general, the midnight narrow flows are termed as subauroral ion drifts and the duskside broader flows are termed subauroral polarization streams (SAPS). SAPS/subauroral ion drift electric fields play an important role in controlling the dynamics of the midlatitude ionosphere. In this paper we analyze longitudinally extended observations of SAPS measured by midlatitude Super Dual Auroral Radar Network (SuperDARN) radars under varied geomagnetic conditions. We find that SAPS speeds exhibit a strong dependence on geomagnetic activity, with flows exceeding 1,500 m/s during geomagnetic storms and dropping to 100 m/s during periods of geomagnetic quiet. Moreover, SAPS flows turn increasingly poleward when moving from the midnight sector toward dusk and this effect is more pronounced during disturbed geomagnetic conditions. The variations in SAPS speeds with magnetic local time (MLT) are also found to be strongly dependent on geomagnetic conditions. Specifically, SAPS speeds increase quasilinearly with MLT during disturbed geomagnetic conditions, whereas during relatively quiet geomagnetic conditions there is no discernible trend. This behavior suggests the possibility of different mechanisms influencing SAPS during geomagnetically quiet conditions. Average cross‐SAPS potentials increase with geomagnetic activity and typically vary between 15 and 45 kV. Finally, a new empirical model of SAPS potentials has been developed parameterized by Asy‐H index, MLT, and magnetic latitude.

Recent Developments in Our Knowledge of Inner Magnetosphere‐Ionosphere Convection

AbstractPlasma convection in the coupled inner magnetosphere‐ionosphere is influenced by different factors such as neutral winds, penetration electric fields, and polarization electric fields. Several crucial insights about the dynamics in the region have been derived by interpreting observations in conjunction with numerical simulations, and recent expansion in ground‐ and space‐based measurements in the region along with improvements in theoretical modeling has fueled renewed interest in the subject. In this paper we present a comprehensive review of the literature with an emphasis on studies since 2012 relevant to the National Science Foundation Geospace Environment Modeling program. We cover four specific areas: (1) the subauroral polarization stream, (2) penetration electric fields, (3) the disturbance dynamo, and (4) quiet time subauroral convection. We summarize new observations and resulting insights relevant to each of these topics and discuss various outstanding issues and unanswered questions.

Energetic Electron Injections Deep Into the Inner Magnetosphere: A Result of the Subauroral Polarization Stream (SAPS) Potential Drop

AbstractIt has been reported that the dynamics of energetic (tens to hundreds of keV) electrons and ions is inconsistent with the theoretical picture in which the large‐scale electric field is a superposition of corotation and convection electric fields. Combining one year of measurements by the Super Dual Auroral Radar Network, DMSP F‐18, and the Van Allen Probes, we show that subauroral polarization streams (SAPSs) are observed when energetic electrons have penetrated below L = 4. Outside the plasmasphere in the premidnight region, potential energy is subtracted from the total energy of ions and added to the total energy of electrons during SAPS onset. This potential energy is converted into radial motion as the energetic particles drift around Earth and leave the SAPS azimuthal sector. As a result, energetic electrons are injected deeper than energetic ions when SAPSs are included in the large‐scale electric field picture, in line with observations.