Energetic Electron Enhancements Research Articles

A comparison of energetic particle energization observations at MMS and injections at Van Allen Probes

In this study, we examine particle energization and injections that show energetic electron enhancements at both MMS in the magnetotail and Van Allen Probes in the inner magnetosphere. Observing injections along with a corresponding flow burst allows us to better understand injections overall. Searching for suitable events, we found that only a small number of events at MMS had corresponding injections that penetrated far enough into the inner magnetosphere to observe with Van Allen Probes. With the four suitable events we did find, we compared the energy spectra at the two spacecraft and mapped the boundary of where the injection entered the inner magnetosphere. We found that, among these injections in the inner magnetosphere, the electron flux did not increase above ∼400 keV, similar to previous results, but the corresponding signatures in the tail observed increased fluxes at 600 keV or higher. There does not appear to be a comparable flux increase at Van Allen Probes and MMS for a given event. None of our injections included ion enhancements at Van Allen Probes, but one included an ion injection at geosynchronous orbit in the GOES spacecraft. All of our injections were dispersed at Van Allen Probes, and we were therefore able to map an estimate of the injection boundary. All of the injections occurred in the premidnight sector. Although we found some events where particle energizations in the tail are accompanied by inner magnetospheric injections, we do not find a statistical link between the two.

Tracking a Beam of Electrons from the Low Solar Corona into Interplanetary Space with the Low Frequency Array, Parker Solar Probe, and 1 au Spacecraft

Type III radio bursts are the result of plasma emission from mildly relativistic electron beams propagating from the low solar corona into the heliosphere where they can eventually be detected in situ if they align with the location of a heliospheric spacecraft. Here we observe a type III radio burst from 0.1 to 16 MHz using the Parker Solar Probe (PSP) FIELDS Radio Frequency Spectrometer (RFS) and from 20 to 80 MHz using the Low Frequency Array (LOFAR). This event was not associated with any detectable flare activity but was part of an ongoing type III and noise storm that occurred during PSP encounter 2. A deprojection of the LOFAR radio sources into 3D space shows that the type III radio burst sources were located on open magnetic field from 1.6 to 3 R ⊙ and originated from a near-equatorial active region around longitude E48°. Combining PSP/RFS observations with WIND/WAVES and Solar Terrestrial Relations Observatory (STEREO) WAVES, we reconstruct the type III radio source trajectory in the heliosphere interior to PSP’s position, assuming ecliptic confinement. An energetic electron enhancement is subsequently detected in situ at the STEREO A spacecraft at compatible times, although the onset and duration suggests the individual burst contributes a subset of the enhancement. This work shows relatively small-scale flux emergence in the corona can cause the injection of electron beams from the low corona into the heliosphere, without needing a strong solar flare. The complementary nature of combined ground and space-based radio observations, especially in the era of PSP, is also clearly highlighted by this study.

A Statistical Study of Magnetopause Boundary Layer Energetic Electron Enhancements Using MMS

We took a survey of boundary layer (or low-latitude boundary layer) crossings by the Magnetospheric Multiscale (MMS) mission. Out of 250 total crossings, about half showed enhancements of high-energy (>30 keV) electrons in the FEEPS sensor and a little less than half of those energetic electron events had whistler-mode waves present. Energetic electron enhancements were more likely to be present at magnetic local times closer to noon and at distances of less than about 20 Earth radii, but there was seemingly no correlation with magnetic latitude. For almost all of these events, the pitch angles of the FEEPS electrons were peaked at 90° or isotropic, not field-aligned. Most of the events for which we had data to make a determination showed either direct or indirect evidence of reconnection. Overall, energetic electron enhancements are a fairly common occurrence and there appears to be some connection between whistler waves, energetic electron enhancements, and reconnection, whether it is a direct link or some other process affecting all of them.

Impact of Space Environment on Geostationary Meteorological Satellite Data Outage

AbstractImpact of space environment changes on geostationary meteorological satellite services, such as data outage, incomplete imagery, or quality degradation were investigated using event logs of Himawari‐8 and Meteosat (MET‐7 and MET‐8) in 2015–2017. The event logs show that such failures were caused by anomalies on spacecraft and in ground system half each. On Himawari‐8, a total of 11 incomplete imagery occurred due to spacecraft anomaly, and among them about 45% (5 anomalies) occurred during energetic electron enhancement and about 9% (1 anomaly) occurred during energetic proton enhancement. In cases of Meteosat, a total of 84 service alerts occurred due to spacecraft anomaly, and among them 35% (29 anomalies) occurred during electron enhancement and 7% (6 anomalies) occurred during both proton and electron enhancement. On the basis of statistical analysis, it is found that the probability of spacecraft anomaly occurrence markedly increases when electron fluence exceeds a threshold. The probability of anomaly is less than 10% when the 1‐MeV electron fluence is less than 104 (/cm2 sr eV), whereas it increases to more than 20% above the fluence. Thresholds are also found for electron fluences at other energies from 200 keV to 1.5 MeV. This study clarifies that changes in the space environment, particularly electron fluence enhancement affect geostationary meteorological satellite services.

Multi‐Event Studies of Sudden Energetic Electron Enhancements in the Inner Magnetosphere and Its Association With Plasmapause Positions

AbstractSudden enhancements of energetic electrons (tens of keV to <500 keV) at low L‐shells have been frequently observed by Van Allen Probes. It is, however, still unclear how deep these electrons can reach and what the responsible mechanisms are. Here we seek to determine the inner boundary of initial enhancements of these energetic electrons and its link with the plasmapause location to offer a new, insightful perspective on this topic. Previous statistical studies have revealed a remarkably consistent observation that initial enhancements of energetic electrons occur mostly at higher L‐shell than the innermost plasmapause locations (Lpp), though a few outlier events were also identified. In this study, we examine the identified outlier events where electron enhancements were reported inside the plasmapause (either in situ Lpp or simulated innermost Lpp). More detailed investigation indicates that the appearance of enhancements inside the in situ Lpp is often associated with duskside observations where the “actual” initial enhancement likely occurs somewhere else, outside the innermost plasmapause location. We thereby urge caution when using the relationship between the observed enhancement locations and the in situ Lpp to infer the effect of electric fields on energetic electrons. In summary, our findings suggest that the innermost Lpp remains the innermost limit of the initial sudden enhancements of energetic electrons. Combining with phase space density analysis, our result implies the role of a large‐scale electric field that leads to sudden electron enhancements and the erosion of the plasmasphere.

Energetic Electron Enhancement and Dropout Echoes Induced by Solar Wind Dynamic Pressure Decrease: The Effect of Phase Space Density Profile

AbstractThe interplanetary (IP) shock with the sudden increase of solar wind dynamic pressure can cause the acceleration and transportation of energetic electrons in the inner magnetosphere. In this study, we further examine the influence of the sudden drop of solar wind dynamic pressure on magnetospheric energetic particles, through case study of energetic electron drift echoes and statistics with 25 cases from 2012 to 2017. We found that there were both dropout and enhancement drift echoes of electrons in some dynamic pressure decrease events, while other events only show electron dropout drift echoes. In addition, we analyzed the electron phase space density (PSD) and found that the radial profile of electron PSD were different for the two types of events, suggesting that the electron PSD plays an important role in the variations of energy electron fluxes induced by the dynamics pressure decrease. The results of this study, combined with previous studies of energetic electron dynamics caused by IP shocks, can provide a more general picture of both solar wind dynamic pressure decrease and increase effects on the energetic electrons.

Characteristics of Energetic Electrons Near Active Magnetotail Reconnection Sites: Statistical Evidence for Local Energization

AbstractMagnetic reconnection is a universal process where energy is transferred from magnetic fields to particles. However, it remains unclear whether this transfer of energy includes the direct energization of particles to high energies (i.e., >10s of keV). We compare the spectral indices of energetic (50–200 keV) electrons from six magnetotail electron diffusion region candidates encountered by MMS with those from “quiet‐time” plasma sheet crossings to test whether energetic electron enhancements result from direct energization at/near the reconnection site or simply focusing high‐energy populations that do not originate from the nearby X‐line and already exist in the plasma sheet along the newly reconnected field lines. The study suggests that active reconnection can be a source of localized electron energization. However, the EDR spectra are not outside the range of those from the quiet‐time plasma sheet, which surprisingly still often have very energetic (up to and beyond 200 keV) electrons present.

Recurrent Solar Energetic Particle Flux Enhancements Observed near Earth and Mars

Abstract The period 2016 August 1 to November 15 was characterized by the presence of corotating interaction regions (CIRs) and a few weak coronal mass ejections (CMEs) in the heliosphere. In this study we show recurrent energetic electron and proton enhancements observed near Earth (1 au) and Mars (1.43–1.38 au) during this period. The observations near Earth use data from instruments on board the Advanced Composition Explorer, the Solar and Heliospheric Observatory, and Solar Dynamics Observatory and those near Mars are from the Solar Energetic Particle, Solar Wind Ion Analyzer, and Magnetometer instruments on board the Mars Atmosphere and Volatile EvolutioN (MAVEN). During this period, the energetic electron fluxes observed near Earth and Mars showed prominent periodic enhancements over four solar rotations, with major periodicities of ∼27 days and ∼13 days. Periodic radar blackouts/weakenings of radar signals at Mars were observed by the Mars Advanced Radar for Subsurface and Ionosphere Sounding/Mars Express, and are associated with these solar energetic electron enhancements. During this period, a weak CME and a high-speed stream (HSS)-related interplanetary shock could have interacted with the CIR and enhance energetic proton fluxes near 1.43–1.38 au, causing ∼27 days periodicity in proton fluxes to be significantly diminished at 1.43–1.38 au. These events also have an unexpected impact on the Martian topside ionosphere, such as topside ionospheric depletion and compression observed by the Langmuir Probe and Waves and Neutral Gas and Ion Mass Spectrometer on board MAVEN. These observations are unique not only because of the recurring nature of electron enhancements seen at two vantage points, but also because they reveal the unexpected impact of the weak CME and interplanetary shock on the Martian ionosphere, which provides new insights into the impact of CME–HSS interactions on the Martian plasma environment.

Energetic electron enhancements under the radiation belt (<i>L</i> < 1.2) during a non-storm interval on 1 August 2008

Abstract. An unusual event of deep injections of >30 keV electrons from the radiation belt to low L shells (L<1.2) in the midnight–dawn sector was found from NOAA/POES observations during quiet geomagnetic conditions on 1 August 2008. Using THEMIS observations in front of the bow shock, we found transient foreshock conditions and interplanetary magnetic field (IMF) discontinuities passing the subsolar region at that time. These conditions resulted in generation of plasma pressure pulses and fast plasma jets observed by THEMIS, respectively, in the foreshock and magnetosheath. Signatures of interactions of pressure pulses and jets with the magnetopause were found in THEMIS and GOES measurements in the dayside magnetosphere and ground magnetogram records from INTERMAGNET. The jets produce penetration of hot magnetosheath plasma into the dayside magnetosphere, as was observed by the THEMIS probes after approaching the magnetopause. High-latitude precipitations of the hot plasma were observed by NOAA/POES satellites on the dayside. The precipitations preceded the >30 keV electron injections at low latitudes. We propose a scenario of possible association between the phenomena observed. However, the scenario cannot be firmly supported because of the lack of experimental data on electric fields at the heights of electron injections. This should be a subject of future experiments.

How Sudden, Intense Energetic Electron Enhancements Correlate With the Innermost Plasmapause Locations Under Various Solar Wind Drivers and Geomagnetic Conditions

AbstractIn this report, the relationship between innermost plasmapause locations (Lpp) and initial electron enhancements during both storm and nonstorm (Dst > −30 nT) periods are examined using data from the Van Allen Probes. The geomagnetic storms are classified into coronal mass ejection (CME)‐driven and corotating interaction region (CIR)‐driven storms to explore their influences on the initial electron enhancements, respectively. We also study nonstorm time electron enhancements and observe frequent, sudden (within two consecutive orbital passes) <400‐keV electron enhancements during quiet periods. Our analysis reveals an incredibly cohesive observation that holds regardless of electron energies (~30 keV–2.5 MeV) or geomagnetic conditions: the innermost Lpp is the innermost boundary of the initial energetic electron enhancements. Interestingly, the quantified energy‐dependent relationship of the sudden, intense energetic electron enhancements, with respect to the innermost Lpp, also exhibit a very similar trend during both storm and nonstorm periods. In summary, the goal of this report is to provide a comprehensive quantification of this consistent relationship under various geomagnetic conditions, which will also enable better forecast and specification of energetic electrons in the inner magnetosphere.

Predictable and unpredictable ionospheric disturbances during St. Patrick's Day magnetic storms of 2013 and 2015 and on 8–9 March 2008

AbstractWe present a comparative analysis of first principles Global Self‐consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) in prediction of ionospheric disturbances during three geomagnetic storms: from moderate on 8–9 March 2008 and on 17–18 March 2013 to strong one on 17–18 March 2015, so‐called St. Patrick's Day storms. We have found that in general, the GSM TIP model gave reasonable prediction of both positive and negative ionospheric storms. Most difficulties have been found for the St. Patrick's Day storms. Namely, a strong positive storm at low latitudes above the Pacific and in the South Atlantic Anomaly region on the main and recovery phases could not be predicted by the model. The positive storm could be explained by ionization effect of energetic electron enhancements. Dynamics of negative ionospheric storms at middle latitudes was predicted by the GSM TIP model quite well though the amplitude of storms was underestimated. The latter could result from underestimation of the N2 contribution especially under unusual conditions of anomalous expansion of auroral precipitations to middle latitudes during the 2015 St. Patrick's Day storm.

What effect do substorms have on the content of the radiation belts?

Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently energized through wave‐particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1–3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM‐H, but decreases in the radiation belt show no apparent link with magnetospheric activity levels.

Energetic Electron Enhancements below the Radiation Belt and X-Ray Contamination at Low-Orbiting Satellites

The work concerns a problem of electron-induced contaminant at relatively low latitudes to high-energy astrophysical measurements on board the low-orbiting satellites. We show the results of a statistical analysis of the energetic electron enhancements in energy range 30–300 keV observed by a fleet of NOAA/POES low-orbiting satellites over the time period from 1999 to 2012. We demonstrate geographical distributions of great and moderate long-lasting enhancements caused by different type of the solar wind drivers.

Electron dynamics in the reconnection ion diffusion region

We investigate and compare Cluster observations of electron dynamics in different locations of the ion diffusion region for magnetic reconnection in the Earth's magnetotail. On the basis of the 2‐D reconstructed magnetic field map from Cluster 1 (C1), we pinpoint that the observed Hall field is ∼6000 km (∼9 ion inertial lengths) away from the magnetic X‐point, and reveal that C3 was the one in closest proximity to the X‐point at the time when the reconnection jet reversal was simultaneously seen by three spacecraft, namely, C1, C3, and C4. No evidence is found for strong wave emission and energetic electron enhancement near to the X‐point, as compared to that within the diffusion region. We find that (1) the Hall current loop is mainly carried by the low‐energy, field‐aligned counterstreaming electrons; (2) a flat‐top distribution in phase space density is a common feature for Hall‐related electrons; (3) an enhancement of energetic electrons is observed together with the presence of the flat‐top electrons; and (4) electromagnetic wave emission is enhanced within the diffusion region. Two different regions of field‐aligned counterstreaming (FC) electrons are identified: one is associated with the Hall current loop (i.e., the electron flow reversal) while another one stays at the edge of the loop. Interestingly, observations show that at the transition between the two FC regions, the waves seem to suppress the energetic electrons but to promote the flat‐top electrons.

Anik‐E1 and E2 satellite failures of January 1994 revisited

The consecutive failures of the geosynchronous Anik‐E1 communication satellite on January 20, 1994, and Anik‐E2 about nine hours later on January 21 (both incidents occurred on January 20 local time) received considerable publicity because the malfunctions of the satellites disrupted television and computer data transmissions across Canada, as well as telephone services to remote northern communities for hours. This often‐cited event is revisited here with materials not covered before. Using publicly available information, Anik‐E failure details, media coverage, recovery effort and cost incurred are first presented. This is then followed by scrutiny of space weather conditions pertinent to the occurrences of the Anik‐E upsets. We trace the space weather episode's inception on the Sun, propagation through interplanetary medium, and manifestation in magnetic field variations as well as in energetic electron flux increases, and its eventual impact on the Anik‐Es. The genesis of the energetic electron enhancements that have been blamed for the satellite malfunctions is thus traceable via high‐speed solar wind stream with Alfven wave fluctuations to a longitudinally wide coronal hole on the Sun. Furthermore, strong magnetic pulsations preceding electron flux peaks indicate Pc5 ULF (Ultra Low Frequency) waves as a probable acceleration mechanism for the energetic electron flux enhancement that resulted in the internal charging of the Anik‐Es. The magnetic fluctuations may even be possible triggers for the subsequent discharge that caused the satellites to malfunction. This incident illustrates that satellite operators should be on alert for elevated high‐energy electron environment that is above established thresholds, as specifications in satellite design may not render a satellite immune from internal charging.

Analysis of a typical internal charging induced spacecraft anomaly

Internal charging is generated by penetrative electrons from the outer radiation belt, and the resultant discharges usually occur inside spacecrafts or sdeeply in the surface dielectrics. Therefore it may produce more serious results in electronics on board compared with surface charging. In this article, the general characteristics of internal charging were introduced, and, as an example, an internal charging induced anomaly, which took place on Double Star (TC-1 and TC-2) was analyzed through correlation of the anomaly with high energetic electron enhancement. The analysis provides a typical instance for spacecraft anomaly diagnostics.

Energetic electron acceleration in the downstream reconnection outflow region

Energetic electrons in an earthward reconnection outflow region have been observed by Cluster/Research with Adaptive Particle Imaging Detectors. We found a good correlation between the energetic electron enhancement and a normal magnetic field (Bz) enhancement within a 0.25‐s time resolution. The large normal magnetic field is thought to be associated with magnetic reconnection because the negative/positive Bz reversal observed during the fast proton tailward/earthward flow reversal is a good indicator of magnetic reconnection. Using the four‐spacecraft Cluster, we can clearly see that this large positive Bz structure propagates in the earthward direction. Furthermore, we find that the energy spectrum of the energetic electrons becomes harder toward the downstream region. A negative Bz enhancement is also observed. The intensity of energetic electron enhancement associated with the negative Bz enhancement is weaker than that associated with the positive one. To discuss the temporal and spatial profile of energetic electron acceleration in the magnetic reconnection region, we determined the spacecraft position in the temporally evolving magnetic structures of reconnection. Our observation clearly indicates second‐step acceleration, in addition to X line acceleration, of energetic electrons in the downstream reconnection outflow region.

Cluster observations of magnetospheric substorm behavior in the near- and mid-tail region

The Cluster constellation of spacecraft has returned substantial new data on particle and field variations in the near- and mid-magnetotail regions of Earth’s magnetosphere. Using the Research with Adaptive Particle Imaging Detectors (RAPID) system onboard the four Cluster vehicles, we have identified substorm-related energetic ( E > 20 keV) electron enhancement events during the period March 2001 through October 2001 in the geocentric radial range of 4–19 Earth radii. We have used concurrent data from other Cluster instruments as well as from the POLAR, IMAGE, FAST, GPS, and geostationary orbit spacecraft in order to understand particle injection and transport phenomena throughout this key region of the magnetotail. Electron enhancements in the plasma sheet at intermediate radial distances have been studied in a global substorm context. A particularly well-observed substorm case occurred on August 27, 2001 when Cluster was almost exactly in the midnight meridian. We find evidence that Cluster was very near the near-Earth substorm neutral line and that magnetic reconnection began some seven minutes prior to the substorm auroral brightening of the expansive phase onset. We also study in some detail the recovery phase of the substorm and the associated expansion of the plasma sheet over the 4-satellite Cluster constellation.

Are energetic electrons in the solar wind the source of the outer radiation belt?

Using data from WIND, SAMPEX (Solar Anomalous, and Magnetospheric Particle Explorer), and the Los Alamos National Laboratory (LANL) sensors onboard geostationary satellites, we investigate the correlation of energetic electrons in the 20–200 keV range in the solar wind and of high speed solar wind streams with relativistic electrons in the magnetosphere to determine whether energetic electrons in the solar wind are the source of the outer relativistic electron radiation belt. Though there is some correlation between energetic electron enhancements in the solar wind and enhancements in the outer radiation belt, the phase space density of 20–200 keV electrons in the solar wind is not adequate to supply the outer radiation belt electrons. Although lower energy electrons in the solar wind could be a seed population of the outer radiation belt, such lower energy electrons cannot achieve relativistic energies through the normal process of radial transport which conserves the first adiabatic invariant. Thus additional internal acceleration processes are required within the magnetosphere to produce the outer radiation belt. High speed solar wind streams are well correlated with increased magnetic activity and with increased fluxes in the outer radiation belt. The maximum correlation between the high speed streams and the radiation belt flux occurs with an increasing time delay for higher energies and and lower L values. We conclude that acceleration processes within the magnetosphere which are well correlated with high speed solar wind streams are responsible for the outer radiation belt electrons.

Energetic (>0.2 MeV) Electron Bursts in the Deep Geomagnetic Tail Observed by ISEE 3: Association with Substorms and Magnetotail Structures

Brief 0.2-2 MeV electron bursts were detected in the plasma sheet, tail lobes and magnetosheath by the Goddard Space Flight Center Medium Energy Cosmic Ray Experiment during the ISEE 3 geotail mission in 1982-3. We summarize the main features of these data and their implications for the structure and dynamics of the geomagnetic tail. Sharp falls in the intensity and occurrence rate of plasma sheet events at ∼90 Re from Earth suggest a change from predominantly closed field lines Earthward of this location to predominantly open field lines at greater distances downtail. The electron anisotropies and associated plasma flows support this proposal which is also consistent with other ISEE 3 observations suggesting that the tail neutral line typically lies at around this distance. Electron bursts in the tail are closely association with substorm activity onsets as indicated by AL intensifications and particle injections at geosynchronous orbit. Signatures of plasmoid ejection down the tail may be observed following electron bursts. In the deep tail, energetic electron enhancements tend to be observed close to the time of substorm onset and are not generally present in the plasma sheet and plasma sheet boundary layer at other times. This suggests that the electrons are accelerated at the substorm neutral line rather than along the current sheet, and are lost rapidly from the tail along open field lines.