Proton Precipitation Research Articles

Statistical survey of storm-time energetic particle precipitation

Energetic particles precipitation, which transmits energy from the magnetosphere to the ionosphere, represents an important coupling process between two systems. In this study, we investigate the spatial distribution and temporal evolution of medium-energy (tens to hundreds of keV) energetic particle precipitation (both ions and electrons) with NOAA/POES observations. We found the following results: (1) During storm time, both energetic electron and proton precipitations exhibit dawn-dusk asymmetry in the equatorial plane, possibly caused by plasma waves that are excited and then interact with energetic electrons and protons at different local times. (2) The energetic proton precipitation appears to contain greater energy flux than electrons in storm time, which is contrary to the low-energy particle precipitation where the electrons carry the dominant precipitation energy. (3) The depth of the earthward inner boundary of precipitation in statistics is linearly correlated with geomagnetic activity levels, represented by the SYM-H index.

Hybrid-Vlasov simulation of auroral proton precipitation in the cusps: Comparison of northward and southward interplanetary magnetic field driving

Particle precipitation is a central aspect of space weather, as it strongly couples the magnetosphere and the ionosphere and can be responsible for radio signal disruption at high latitudes. We present the first hybrid-Vlasov simulations of proton precipitation in the polar cusps. We use two runs from the Vlasiator model to compare cusp proton precipitation fluxes during southward and northward interplanetary magnetic field (IMF) driving. The simulations reproduce well-known features of cusp precipitation, such as a reverse dispersion of precipitating proton energies, with proton energies increasing with increasing geomagnetic latitude under northward IMF driving, and a nonreversed dispersion under southward IMF driving. The cusp is also found more polewards in the northward IMF simulation than in the southward IMF simulation. In addition, we find that the bursty precipitation during southward IMF driving is associated with the transit of flux transfer events in the vicinity of the cusp. In the northward IMF simulation, dual lobe reconnection takes place. As a consequence, in addition to the high-latitude precipitation spot associated with the lobe reconnection from the same hemisphere, we observe lower-latitude precipitating protons which originate from the opposite hemisphere’s lobe reconnection site. The proton velocity distribution functions along the newly closed dayside magnetic field lines exhibit multiple proton beams travelling parallel and antiparallel to the magnetic field direction, which is consistent with previously reported observations with the Cluster spacecraft. In both runs, clear electromagnetic ion cyclotron waves are generated in the cusps and might further increase the calculated precipitating fluxes by scattering protons to the loss cone in the low-altitude cusp. Global kinetic simulations can improve the understanding of space weather by providing a detailed physical description of the entire near-Earth space and its internal couplings.

Model‐Based Properties of the Dayside Open/Closed Boundary: Is There a UT‐Dependent Variation?

AbstractThe open‐closed boundary (OCB) defines a region of significant transformation in Earth's protective magnetic shield. Principle among these changes is the transition of magnetic field lines from having two foot points, one in each hemisphere, to one foot point at Earth, the other mapping to the solar wind. Charged particles in the solar wind are able to follow these open field lines into Earth's upper atmosphere. The OCB also defines the polar cap boundary. Being able to identify and track the OCB allows study of several components of the geomagnetic system. Among them are the electrodynamics of the geomagnetic field and the reconnection balance between the dayside and nightside of the geomagnetic field. Furthermore, the OCB can provide insights into the precipitation of energetic protons into the ionosphere. Using the Tsyganenko model of the geomagnetic field (T96), we demonstrate a diurnal fluctuation which we call the Universal Time (UT) effect of the OCB. This UT effect is independent of all other inputs. We anticipate this UT effect to have important consequences in modeling the OCB and other polar cap‐associated structures, especially polar cap absorption events that adversely affect high‐frequency radio wave propagation in polar regions.

Magnetic local time asymmetries in precipitating electron and proton populations with and without substorm activity

Abstract. The magnetic local time (MLT) dependence of electron (0.15–300 keV) and proton (0.15–6900 keV) precipitation into the atmosphere based on National Oceanic and Atmospheric Administration POES and METOP satellite data during 2001–2008 was described. Using modified APEX coordinates the influence of particle energy, substorm activity and geomagnetic disturbance on the MLT flux distribution was statistically analysed. Some of the findings are the following. a. Substorms mostly increase particle precipitation in the night sector by about factor 2–4, but can also reduce it in the day sector.b. MLT dependence can be assigned to particles entering the magnetosphere at the cusp region and magnetospheric particles in combination with energy-specific drifts (in agreement with Newell et al., 2009).c. MLT flux differences of up to 2 orders of magnitude have been identified inside the auroral oval during geomagnetically disturbed conditions. The novelty here is the comprehensive coverage of energy bands and the focus on asymmetry.d. The maximum flux asymmetry ratio depends on particle energy, decreasing with Kp for low energetic particles and increasing with Kp for higher energy electrons, while high energy protons show a more complex dependency. While some aspects may already have been known, the quantification of the flux asymmetry sheds new light on MLT variation.

Direct Observation of Subrelativistic Electron Precipitation Potentially Driven by EMIC Waves

AbstractElectromagnetic ion cyclotron (EMIC) waves are known to typically cause electron losses into Earth's upper atmosphere at >~1 MeV, while the minimum energy of electrons subject to efficient EMIC‐driven precipitation loss is unresolved. This letter reports electron precipitation from subrelativistic energies of ~250 keV up to ~1 MeV observed by the Focused Investigations of Relativistic Electron Burst Intensity, Range and Dynamics (FIREBIRD‐II) CubeSats, while two Polar Operational Environmental Satellites (POES) observed proton precipitation nearby. Van Allen Probe A detected EMIC waves (~0.7–2.0 nT) over the similar L shell extent of electron precipitation observed by FIREBIRD‐II, albeit with a ~1.6 magnetic local time (MLT) difference. Although plasmaspheric hiss and magnetosonic waves were also observed, quasi‐linear calculations indicate that EMIC waves were the most efficient in driving the electron precipitation. Quasi‐linear theory predicts efficient precipitation at >0.8–1 MeV (due to H‐band EMIC waves), suggesting that other mechanisms are required to explain the observed subrelativistic electron precipitation.

Simultaneous Observations of EMIC Waves, ELF/VLF Waves, and Energetic Particle Precipitation during Multiple Compressions of the Magnetosphere

Simultaneous observations of ELF/VLF and EMIC waves from Van Allen Probe satellites in the daytime Earth’s magnetosphere and on the ground during multiple compressions of the magnetosphere due to the fluctuations of the dynamic pressure of the solar wind are considered. Each magnetospheric compression leads to the generation of a wave burst in these frequency ranges. Based on data on the spectral and amplitude characteristics of the waves, measurements of the magnetic field, and the cold plasma density, the pitch-angle diffusion coefficients of protons and electrons in the vicinity of the loss cone are calculated. It is shown that ELF waves with frequencies of 30 keV) electrons; VLF waves at frequencies of 2–5 kHz may be responsible for precipitation of electrons with energy of ~1 keV. The EMIC waves observed from satellites and on the ground are related to the precipitation of protons with energies of 10–100 keV. The particle energies that correspond to the maxima of the diffusion coefficient are compared with the energies of the charged particles precipitating into the ionosphere, which were determined based on data from low-orbit POES satellites, and it is shown that they are in a good agreement with each other.

Quiet Time Structured Pc1 Waves Generated During Transient Foreshock

AbstractWe study two events of structured Pc1 waves (pearls) observed by CARISMA magnetometers during a period of quiet magnetic (Kp ~1) and solar wind conditions on 1 August 2008. Bursts of proton precipitations and electromagnetic ion‐cyclotron waves were simultaneously observed by NOAA/POES and GOES satellites at dayside. Apparent correspondence was found between ground pearl pulsations and magnetospheric compressions observed by GOES and THEMIS satellites. We have found the Pc1 wave splitting into very close subfrequencies (within 0.1 Hz) that can be explained by weak magnetospheric compressions. The compressions are caused by pressure pulses originated from transient foreshock and interplanetary magnetic field discontinuities observed upstream of the bow shock by the THEMIS‐C probe. Thus, the observed pearls are compression‐related Pc1 waves generated under transient foreshock conditions.

Properties of Localized Precipitation of Energetic Protons Equatorward of the Isotropic Boundary

AbstractUsing National Oceanic and Atmospheric Administration Polar Orbiting Environmental Satellite (NOAA/POES) observations of energetic protons, we for the first time investigated statistical properties of a specific type of particle precipitation—localized precipitation of energetic protons (LPEP) equatorward of the isotropy boundary. The maximum occurrence rate was found in the day‐afternoon sector at L > 6. The maximum precipitating flux is found at lower L shells (L = 4–5). The dependence of LPEP occurrence and intensity on the geomagnetic activity indices and solar wind parameters is investigated. In particular, while the precipitating proton flux increases with geomagnetic activity everywhere, the occurrence rate in the day‐afternoon sector at L > 6 decreases under the strongest activity. We conclude that revealed LPEP properties are mostly similar to those obtained for electromagnetic ion cyclotron waves on the basis of data from previous spacecraft missions. This similarity supports the suggestion on LPEP as the result of ion cyclotron instability in the magnetosphere.

Effects of Energetic Electron and Proton Precipitations on Thermospheric Nitric Oxide Cooling During Shock‐Led Interplanetary Coronal Mass Ejections

AbstractSatellite measurements have revealed significant enhancement of 5.3‐μm nitric oxide (NO) emission during shock‐led interplanetary coronal mass ejections. Great discrepancies in modeled neutral density occur during these events and may be attributed to the abnormally high NO cooling. Meanwhile, the relative significance of protons, soft electrons, and keV‐electrons to NO emission is yet to be well determined. The goal of this study is to identify the contribution of electron and proton precipitations to the thermospheric NO cooling by using the Defense Meteorological Satellite Program (DMSP) data. The observed energetic electrons and protons (0.1–30.2 keV) during 36 shock‐led interplanetary coronal mass ejection events in 2002–2010 are binned into geomagnetic grids to provide statistical distributions of the particle precipitation for polar regions. The distributions are incorporated into the Global Ionosphere‐Thermosphere Model. The results show that electrons play a dominant role to NO cooling, but protons are also important and contribute to up to a quarter of NO cooling by electrons and ions combined. NO cooling enhancement during the events is proportional to the level of energy flux and is dominated by the electrons in the energy band of 1.4–3.1 keV. Both total electron content (TEC) and NO cooling enhance at the source regions, but they have different lifetime and correlation with the particle precipitations. Generally, NO cooling and TEC enhancements have a positive correlation with the precipitating energy. Cross correlation shows that particle precipitations have more instantaneous impact on TEC while it takes longer for the atmosphere to heat up for cooling to proceed.

Kinetic Monte Carlo Model for the Precipitation of High-Energy Protons and Hydrogen Atoms into the Atmosphere of Mars with Taking into Account the Measured Magnetic Field

Results of model computations of the interaction of the high-energy protons and hydrogen atoms (H/H+) precipitating into the Martian atmosphere are presented. These computations were performed using a modification of the kinetic Monte Carlo model developed earlier for the analysis of the data from the MEX/ASPERA-3 instrument onboard the Mars Express spacecraft and the MAVEN/SWIA instrument onboard the MAVEN spacecraft. In this modification of the model, an arbitrary (three-dimensional) structure of the magnetic field of Mars is taken into account for the first time. With local measurements of all three components of the magnetic field, not only the flux of protons penetrating into the atmosphere, but also the degradation of the H/H+ flux along the spacecraft orbit and the formation of upward fluxes of protons and hydrogen atoms scattered by the atmosphere, can now be described. A comparison of simulations and measurements of proton fluxes at low altitudes are used to infer the efficiency of charge exchange between the solar wind and the extended Martian hydrogen corona. It was found that the induced magnetic field plays a very important role in the formation of the proton flux back-scattered by the atmosphere and strongly controls its magnitude.

Hybrid-Vlasov modelling of nightside auroral proton precipitation during southward interplanetary magnetic field conditions

Abstract. Particle precipitation plays a key role in the coupling of the terrestrial magnetosphere and ionosphere by modifying the upper atmospheric conductivity and chemistry, driving field-aligned currents, and producing aurora. Yet quantitative observations of precipitating fluxes are limited, since ground-based instruments can only provide indirect measurements of precipitation, while particle telescopes aboard spacecraft merely enable point-like in situ observations with an inherently coarse time resolution above a given location. Further, orbit timescales generally prevent the analysis of whole events. On the other hand, global magnetospheric simulations can provide estimations of particle precipitation with a global view and higher time resolution. We present the first results of auroral (∼1–30 keV) proton precipitation estimation using the Vlasiator global hybrid-Vlasov model in a noon–midnight meridional plane simulation driven by steady solar wind with a southward interplanetary magnetic field. We first calculate the bounce loss-cone angle value at selected locations in the simulated nightside magnetosphere. Then, using the velocity distribution function representation of the proton population at those selected points, we study the population inside the loss cone. This enables the estimation of differential precipitating number fluxes as would be measured by a particle detector aboard a low-Earth-orbiting (LEO) spacecraft. The obtained differential flux values are in agreement with a well-established empirical model in the midnight sector, as are the integral energy flux and mean precipitating energy. We discuss the time evolution of the precipitation parameters derived in this manner in the global context of nightside magnetospheric activity in this simulation, and we find in particular that precipitation bursts of <1 min duration can be self-consistently and unambiguously associated with dipolarising flux bundles generated by tail reconnection. We also find that the transition region seems to partly regulate the transmission of precipitating protons to the inner magnetosphere, suggesting that it has an active role in regulating ionospheric precipitation.

Diffuse Auroral Electron and Ion Precipitation Effects on RCM-E Comparisons With Satellite Data During the 17 March 2013 Storm.

Effects of scattering of electrons from whistler chorus waves and of ions due to field line curvature on diffuse precipitating particle fluxes and ionospheric conductance during the large 17 March 2013 storm are examined using the self-consistent Rice Convection Model Equilibrium (RCM-E) model. Electrons are found to dominate the diffuse precipitating particle integrated energy flux, with large fluxes from ~21:00 magnetic local time (MLT) eastward to ~11:00 MLT during the storm main phase. Simulated proton and oxygen ion precipitation due to field line curvature scattering is sporadic and localized, occurring where model magnetic field lines are significantly stretched on the night side at equatorial geocentric radial distances r 0 ≳8 R E and/or at r 0 ~5.5 to 6.5 R E from dusk to midnight where the partial ring current field has perturbed the magnetic field. The precipitating protons likewise contribute sporadically to the storm time Hall and Pedersen conductance in localized regions whereas the precipitating electrons are the dominate storm time contributor to enhanced Hall and Pedersen conductance at auroral magnetic latitudes on the night and morning side. The RCM-E model can reproduce general features of the Van Allen Probe/MagEIS observed trapped electron differential flux spectrograms over energies of ~37 to 150 keV. The simulations with a parameterized electron loss model also reproduce reasonably well the storm time Defense Meteorological Satellite Program integrated electron energy flux at 850 km at satellite crossings from predawn to midmorning. However, model-data agreement is not as good from dusk to premidnight where there are large uncertainties in the electron loss model.

Lyman-α emission in the Martian proton aurora: Line profile and role of horizontal induced magnetic field

Enhancements of the dayside Lyman-α emission by as much as ∼50% have been observed between 120 and 130 km in the lower Martian thermosphere from the Mars Express and MAVEN satellites, usually following solar events such as coronal mass ejections and corotating interaction regions. They have been assumed to be optical signatures of proton aurora related to an increase in the solar wind proton flux hitting Mars’ bow shock. We present model simulations of the Lyman-α line profiles at different altitudes. These are partly guided by in situ measurements of the energy spectrum of protons in the magnetosheath region by the SWIA instrument on board the MAVEN spacecraft. We show that the auroral Lyman-α line profile is significantly broader than the hydrogen core of the planetary thermal H atom. Consequently, most of the auroral emission is produced outside the optically thick hydrogen core and creates the observed intensity enhancement. Simulations with incident energetic hydrogen atoms (H ENAs) produce a somewhat broader line profile. Monte Carlo calculations are made separately for incident solar wind protons and H ENAs produced by charge exchange in the hydrogen corona. Absorption by CO2 along the line of sight significantly affects the intensity distribution in the lower thermosphere. The calculated altitude of the peak emission for both types of incident particles is consistent with the observed characteristics of the proton aurora. We show that the presence of a horizontal induced magnetic field somewhat increases the line width and decreases the altitude of the emission peak as a consequence of the magnetic barrier effect on proton precipitation. The brightness of the Lyman-α emission also drops as a result of increased magnetic shielding of the protons.

Proton Auroras Equatorward of the Oval as a Manifestation of the Ion-Cyclotron Instability in the Earth’s Magnetosphere (Brief Review)

Different types of proton auroras observed by the IMAGE satellite equatorward of the proton aurora oval are briefly reviewed. These auroras are caused by the precipitation of energetic protons from the Earth’s magnetosphere during the development of the ion-cyclotron instability. In addition to the previously considered types of proton auroras (spots, evening arcs, and dayside flashes), a new type is described: longlasting proton auroras on the dayside. The scheme of interrelation between different proton auroras equatorward of the oval with the distribution of cold plasmaspheric plasma is given.

A Statistical Study to Determine the Origin of Long-duration Gamma-Ray Flares

Abstract Two scenarios have been proposed to account for sustained ≥30 MeV gamma-ray emission in solar flares: (1) prolonged particle acceleration/trapping involving large-scale magnetic loops at the flare site, and (2) precipitation of high-energy (>300 MeV) protons accelerated at coronal/interplanetary shock waves. To determine which of these scenarios is more likely, we examine the associated soft X-ray flares, coronal mass ejections (CMEs), and solar energetic proton events for (a) the long-duration gamma-ray flares (LDGRFs) observed by the Large Area Telescope on Fermi, and (b) delayed and/or spatially extended high-energy gamma-ray flares observed by the Gamma-ray Spectrometer on the Solar Maximum Mission, the Gamma-1 telescope on the Gamma satellite, and the Energetic Gamma-Ray Experiment Telescope on the Compton Gamma-Ray Observatory. For the Fermi data set of 11 LDGRFs with >100 MeV emission lasting for ≥∼2 hr, we search for associations and reverse associations between LDGRFs, X-ray flares, CMEs, and SEPs, i.e., beginning with the gamma-ray flares and also, in turn, with X-class soft X-ray flares, fast (≥1500 km s−1) and wide CMEs, and intense (peak flux ≥2.67 × 10−3 protons cm−2 s−1 sr−1, with peak to background ratio >1.38) >300 MeV SEPs at 1 au. While LDGRFs tend to be associated with bright X-class flares, we find that only one-third of the X-class flares during the time of Fermi monitoring coincide with an LDGRF. However, nearly all fast, wide CMEs are associated with an LDGRF. These preliminary association analyses favor the proton precipitation scenario, although there is a prominent counter-example of a potentially magnetically well-connected solar eruption with >100 MeV emission for ∼10 hr for which the near-Earth >300 MeV proton intensity did not rise above background.

EMIC Wave Events During the Four GEM QARBM Challenge Intervals

AbstractThis paper presents observations of electromagnetic ion cyclotron (EMIC) waves from multiple data sources during the four Geospace Environment Modeling challenge events in 2013 selected by the Geospace Environment Modeling Quantitative Assessment of Radiation Belt Modeling focus group: 17 and 18 March (stormtime enhancement), 31 May to 2 June (stormtime dropout), 19 and 20 September (nonstorm enhancement), and 23–25 September (nonstorm dropout). Observations include EMIC wave data from the Van Allen Probes, Geostationary Operational Environmental Satellite, and Time History of Events and Macroscale Interactions during Substorms spacecraft in the near‐equatorial magnetosphere and from several arrays of ground‐based search coil magnetometers worldwide, as well as localized ring current proton precipitation data from low‐altitude Polar Operational Environmental Satellite spacecraft. Each of these data sets provides only limited spatial coverage, but their combination shows consistent occurrence patterns and reveals some events that would not be identified as significant using near‐equatorial spacecraft alone. Relativistic and ultrarelativistic electron flux observations, phase space density data, and pitch angle distributions based on data from the Relativistic Electron‐Proton Telescope and Magnetic Electron Ion Spectrometer instruments on the Van Allen Probes during these events show two cases during which EMIC waves are likely to have played an important role in causing major flux dropouts of ultrarelativistic electrons, particularly near L* ~4.0. In three other cases, identifiable smaller and more short‐lived dropouts appeared, and in five other cases, these waves evidently had little or no effect.

Generation of EMIC Waves in the Magnetosphere and Precipitation of Energetic Protons: Comparison of the Data from THEMIS High Earth Orbiting Satellites and POES Low Earth Orbiting Satellites

Regions of the detection of electromagnetic ion-cyclotron (EMIC) waves on the THEMIS satellites near the equatorial plane and the precipitation of energetic protons on POES low Earth orbiting satellites are compared with the magnetospheric magnetic field model. It is confirmed that low Earth orbiting satellites detect the precipitation of energetic protons in the regon associated with observations of EMIC waves in the magnetosphere. This is consistent with the idea that protons are scattered in the loss cone as a result of ioncyclotron interaction. Thus, observations of fluxes of energetic protons in low Earth orbits can be used to monitor ion-cyclotron instability regions in the magnetosphere. Simultaneous observations at high and low Earth orbits contribute to the construction of a spatiotemporal pattern of the interaction region of EMIC waves and energetic protons. In addition, it is shown that proton precipitation associated with EMIC waves can cause errors in determining the latitude of the isotropic boundary (the equatorial boundary of isotropic fluxes of energetic protons), which is an indicator of the configuration of the magnetic field in the magnetosphere.

Monte Carlo Simulations of the Interaction of Fast Proton and Hydrogen Atoms With the Martian Atmosphere and Comparison With In Situ Measurements

AbstractWe present model results of the interaction of proton and hydrogen atom precipitation with the Martian atmosphere. We use a kinetic Monte Carlo model developed earlier for the analysis of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA‐3) Mars Express data. With the availability of Mars Atmosphere and Volatile Evolution Mission in situ measurements, not only the flux of protons incident on the atmosphere but also their degradation along the orbit may now be described. The comparison of the simulations with data collected with the Solar Wind Ion Analyzer shows that the Monte Carlo model reproduces some of the measured features. The results of comparison between simulations and measurements of the proton fluxes at low altitudes make it possible to infer the efficiency of charge exchange between solar wind and the extended hydrogen corona if the value of the magnetic field is measured simultaneously. We also find that the induced magnetic field plays a very important role in the formation of the backscattered flux and strongly controls its magnitude. At the same time, discrepancies between the modeled and the measured energy spectra of the backscattered protons are pointed out. We suggest that some of the physical processes controlling the upward flux are not fully understood or that the data processing of the measured backscattered proton flux should be improved.

A Statistical Study of Spatial Variation of Relativistic Electron Precipitation Energy Spectra With Polar Operational Environmental Satellites

AbstractThe mechanisms that drive relativistic electron precipitation (REP) from the radiation belts can be better understood with a better knowledge of the particle energies involved. National Oceanic and Atmospheric Administration Polar Operational Environmental Satellites, being a network of multiple satellites, can provide multiple point spectral data over a long time period, including the Van Allen Probe's era. The number of energy channels is limited, but the particle detectors on Polar Operational Environmental Satellites have a narrow field of view allowing an investigation of bounce loss cone particles. We use the ratio of count rates in the E3 (>300 keV) and the P6 (>700 keV) channels as a parameter to define spectral hardness. Using this parameter, the spatial variation of spectral hardness of REP events was investigated. It was found that very soft events were mostly found in the dusk‐midnight‐early morning magnetic local time sectors and L∼ 5–7 while the hardest events were located in the postnoon sector peaking at L∼ 4–5. The hardest events peaked at lower L shells, and less than 20% were coincident with low‐energy (30–80 keV) proton precipitation. Further, around 70% of nightside REP coincident with proton precipitation was associated with stretched magnetic field lines indicating that curvature scattering may have been an important driver. Around 62% of nightside REP coincident with proton precipitation associated with relaxed magnetic field lines, suggesting a mechanism other than magnetic field curvature scattering, was highly energetic.

A Statistical Study of the Spatial Extent of Relativistic Electron Precipitation With Polar Orbiting Environmental Satellites

AbstractRelativistic electron precipitation (REP) in the atmosphere can contribute significantly to electron loss from the outer radiation belts. In order to estimate the contribution to this loss, it is important to estimate the spatial extent of the precipitation region. We observed REP with the zenith pointing (0°) Medium Energy Proton Electron Detector (MEPED) on board Polar Orbiting Environmental Satellites (POES), for 15 years (2000–2014) and used both single‐satellite and multisatellite measurements to estimate an average extent of the region of precipitation in L shell and magnetic local time (MLT). In the duration of 15 years (2000–2014), 31,035 REP events were found in this study. Events were found to split into two classes; one class of events coincided with proton precipitation in the P1 channel (30–80 keV), were located in the dusk and early morning sector, and were more localized in L shell (dL < 0.5), whereas the other class of events did not coincide with proton precipitation, were located mostly in the midnight sector, and were wider in L shell (dL ∼ 1–2.5). Both classes were highly localized in MLT (dMLT ≤ 3 h), occurring mostly during the declining phase of the solar cycle and geomagnetically active times. The events located in the midnight sector for both classes were found to be associated with tail magnetic field stretching which could be due to the fact that they tend to occur mostly during geomagnetically active times or could imply that precipitation is caused by current sheet scattering.