Electron Flux Measurements Research Articles

A numerical study of unusual flux decreases for cosmic ray protons and electrons observed by Alpha Magnetic Spectrometer in 2017

Alpha Magnetic Spectrometer (AMS), installed on the International Space Station, delivers precision measurements of cosmic proton fluxes and electron fluxes, providing unique inputs to further improve our understanding of the solar modulation of cosmic protons and electrons. The latest measurements published by AMS show significant decreases in daily cosmic proton fluxes and electron fluxes in the second half of 2017 (approximately from June 11, 2017 to December 23, 2017). A special structure, known as a loop, appears in the electron-proton hysteresis during this period. These declining fluxes, as well as their recovery toward solar minimum modulation, could be attributed to solar wind structures such as global merged interaction regions (GMIRs), which can affect cosmic ray flux for several months, as well as coronal mass ejections (CMEs). We aim to find the reason for the decrease and clarify the solar modulation mechanism underlying the loop structure. We developed a 3D numerical model based on Parker transport equation, which is solved as a set of stochastic differential equations, combined with diffusion barriers propagating away from the Sun. Correspondingly, the relevant parameters can be tuned up. The unusual changes in cosmic proton fluxes and electron fluxes in the second half of 2017 could be caused by CMEs and GMIRs. The decreases in these fluxes in 2017, with rigidities below 11 GV, have been successfully reproduced. Daily variations at Earth in terms of the diffusion coefficients (and their mean-free paths) were subsequently obtained. Furthermore, our simulation reveals that the electron-proton hysteresis loop structure in 2017 results from the different responses of protons and electrons to solar modulation, especially with respect to drift and diffusion processes in the heliosphere.

Statistical Relationship Between Electron Flux and Resonant Chorus Wave Power Near the Flux Limit

AbstractElectron precipitation by chorus whistler‐mode waves generated by the same electron population is expected to play an important role in the dynamics of the outer radiation belt, potentially setting a hard upper limit on trapped energetic electron fluxes. Here, we statistically analyze the relationship between equatorial electron fluxes and the power of mid‐latitude cyclotron‐resonant chorus waves precipitating these electrons, both inferred from ELFIN low‐altitude energy and pitch‐angle resolved electron flux measurements in 2020–2022. We provide clear evidence of a flux limitation coinciding with an exponential increase of precipitation. We statistically demonstrate that the actual inferred resonant wave power gains are well correlated with theoretical linear gains, as in the classical Kennel‐Petschek model, for moderately high linear gains and high fluxes. However, we also find a finite occurrence of very high fluxes, corresponding to resonant waves of moderate average amplitude, implying a softer, more dynamical upper limit than traditionally envisioned.

Derivations of the Total Radiation Belt Electron Content.

We present multiple derivations of the Total Radiation Belt Electron Content (TRBEC), an indicator of the global number of electrons that instantaneously occupy the radiation belts. Derived from electron flux measurements, the TRBEC reduces the spatial information into a scalar quantity that concisely describes global aspects of the system. This index provides a simple, global, and long-term assessment of the radiation belts that enables systematic analysis. In this work, we examine the TRBEC using the adiabatic invariants of which has been used in previous articles as this coordinate system removes reversible adiabatic effects. We then introduce a new expression to compute the TRBEC using the non-adiabatic coordinates of , relevant in the contexts of energetic electron precipitation, chorus, and hiss scattering where adiabatic invariant quantities are no longer conserved. From both expressions of the TRBEC we demonstrate that an erroneous factor of that appeared in previous works using the adiabatic derivation led to an overestimate of the reported electron populations. In addition, we quantify electron loss in the outer radiation belt via a case study using the Van Allen Probes data over a 20-day period from March 2013 specifying particle populations both in terms of the aforementioned adiabatic and non-adiabatic variables. The total number of electrons in the outer radiation belt reached upwards of electrons at the peak of the storm, a rest mass of roughly 10g.

Optical measurements of precipitating relativistic electron microbursts during geomagnetic disturbance and pulsating aurora

Mechanisms of formation and losses of radiation belts are the most important questions of magnetospheric physics, especially in a subsecond temporal scale. Energetic particles release their energy in the atmosphere producing fluorescent emission in characteristic wavelength bands. This emission is measurable and can be an additional information source on the spatiotemporal structure of particle fluxes and spectra. Here we present the world’s first measurements of UV-microbursts during geomagnetic disturbance and pulsating aurora caused by high-energy electron precipitation. It demonstrates that fundamental questions of magnetospheric physics mentioned above can be addressed by using the optical measurements by highly sensitive photometers with high temporal resolution. Such a photometer was installed at Verkhnetulomsky observatory at Kola Peninsula and measured a series of short (less than 0.5 s) pulses of emission with an angular size of bright spot ∼0.2 rad. Simultaneous measurements of high-energy electron fluxes made by the NOAA-19 satellite and fine temporal structure of geomagnetic pulsations demonstrate a magnetospheric origin of the observed events.

Nightside Electron Precipitation Patterns as Observed by ELFIN and CIRBE CubeSats

AbstractThe rapidly expanding fleet of low‐altitude CubeSats equipped with energetic particle detectors brings new opportunities for monitoring the dynamics of the radiation belt and near‐Earth plasma sheet. Despite their small sizes, CubeSats can carry state‐of‐the‐art instruments that provide electron flux measurements with finer energy resolution and broader energy coverage, compared to conventional missions such as POES satellites. The recently launched CIRBE CubeSat measures 250–6,000 keV electrons with extremely high energy resolution, however, CIRBE typically only measures locally‐trapped electrons and cannot directly measure the precipitating electrons. This work aims to develop a technique for identifying indications of nightside precipitation using the locally‐trapped electron measurements by the CIRBE CubeSat. This study focuses on two main types of drivers for nightside precipitation: electron scattering by the curvature of magnetic field lines in the magnetotail current sheet and electron scattering by resonance with electromagnetic ion cyclotron (EMIC) waves. Using energy and pitch‐angle resolved electron fluxes from the low‐altitude ELFIN CubeSat, we reveal the features that distinguish between these two precipitation mechanisms based solely on locally‐trapped flux measurements. Then we present measurements from four CIRBE orbits and demonstrate the applicability of the proposed technique to the investigation of nightside precipitation using CIRBE observations, enabling separation between precipitation induced by curvature scattering and EMIC waves in nearby regions. Our study underscores the feasibility of employing high‐energy‐resolution CIRBE measurements for detecting nightside precipitation of relativistic electrons. Additionally, we briefly discuss outstanding scientific questions about these precipitation patterns that could be addressed with CIRBE measurements.

ELFIN‐GPS Comparison of Energetic Electron Fluxes: Modeling Low‐Altitude Electron Flux Mapping to the Equatorial Magnetosphere

AbstractNear‐equatorial measurements of energetic electron fluxes, in combination with numerical simulation, are widely used for monitoring of the radiation belt dynamics. However, the long orbital periods of near‐equatorial spacecraft constrain the cadence of observations to once per several hours or greater, that is, much longer than the mesoscale injections and rapid local acceleration and losses of energetic electrons of interest. An alternative approach for radiation belt monitoring is to use measurements of low‐altitude spacecraft, which cover, once per hour or faster, the latitudinal range of the entire radiation belt within a few minutes. Such an approach requires, however, a procedure for mapping the flux from low equatorial pitch angles (near the loss cone) as measured at low altitude, to high equatorial pitch angles (far from the loss cone), as necessitated by equatorial flux models. Here we do this using the high energy resolution ELFIN measurements of energetic electrons. Combining those with GPS measurements we develop a model for the electron anisotropy coefficient, , that describes electron flux dependence on equatorial pitch‐angle, , . We then validate this model by comparing its equatorial predictions from ELFIN with in‐situ near‐equatorial measurements from Arase (ERG) in the outer radiation belt.

The Global Characteristics of Electrons Near the Inner Edge of the Inner Radiation Belt

AbstractEnergetic electrons around the inner edge of the inner radiation belt (L1.3) have not been studied to the extent of the rest of the inner belt and certainly not to that of the outer radiation belt. Yet, the behavior of electrons at the inner edge of the inner belt could improve our understanding of important dynamics deep within Earth's magnetosphere. Previous work has analyzed these electrons during either isolated events or via significantly limited statistical studies, and it remains unclear what the particular drivers of electron flux enhancements in this region may be. Here, we present a broad statistical study of electrons around the inner edge of the inner radiation belt, utilizing the 7‐year data set of the MagEIS particle detectors aboard both Van Allen Probes spacecraft. Moreover, we separate electron flux measurements into stably trapped and quasi‐trapped electrons and directly compare their behavior. We find both populations to be variable in L and energy, as well as showing a clear magnetic local time (MLT) asymmetry. Potential drivers are also explored, where we demonstrate an association between increased electron fluxes in this region and heightened solar wind speed, Sym‐H, dynamic pressure, southward IMF and most prominently with the AU and AL indices.

Checking Key Assumptions of the Kennel‐Petschek Flux Limit With ELFIN CubeSats

AbstractIn planetary radiation belts, the Kennel‐Petschek flux limit is expected to set an upper limit on trapped electron fluxes at 80–600 keV in the presence of efficient electron loss through pitch‐angle diffusion by whistler‐mode chorus waves generated around the magnetic equator by the same 80–600 keV electron population. Comparisons with maximum measured fluxes have been relatively successful, but several key assumptions of the Kennel‐Petschek model have not been experimentally tested. The Kennel‐Petschek model notably assumes an exponential growth of chorus waves as the trapped electron flux increases, and a fixed maximum wave power gain of about 3. Here, we describe a method for inferring the near‐equatorial wave power gain using only measurements of trapped, precipitating, and backscattered electron fluxes at low altitude. Next, we make use of Electron Losses and Fields Investigation (ELFIN) CubeSats measurements of such electron fluxes during two moderate geomagnetic storms with sustained electron injections to infer the corresponding chorus wave power gains as a function of time, energy, and equatorial trapped electron flux. We show that wave power increases exponentially with trapped flux, with a wave power gain roughly proportional to the theoretical linear convective gain, and that the maximum inferred gain near the upper flux limit is roughly 10, with a factor of 2 uncertainty. Therefore, two key theoretical underpinnings of the Kennel‐Petschek model are borne out by the present results, although the strong inferred gains should correspond to higher flux limits than in traditional estimates.

Observations of Relativistic Electron Enhancement and Butterfly Pitch Angle Distributions at Low L (<3)

AbstractElectrons in Earth's outer radiation belt are highly dynamic, with fluxes changing by up to orders of magnitude. The penetration of electrons from the outer belt to the inner belt is one such change observed during geomagnetic storms and was previously observed in electrons up to 1 MeV for some strong storms observed by the Van Allen Probes. We analyze pulse height analysis data from the Relativistic Electric and Proton Telescope (REPT) on the Van Allen Probes to produce electron flux measurements with lower minimum energy and significantly improved resolution compared to the standard REPT data and show that electron penetrations into the inner belt (L ≤ 2) extend to at least 1.3 MeV and penetrations into the slot region (2 < L < 2.8) extend to at least 1.5 MeV during certain geomagnetic storms. We also demonstrate that these penetrations are associated with butterfly pitch angle distributions from 1 to 1.3 MeV.

Can We Intercalibrate Satellite Measurements by Means of Data Assimilation? An Attempt on LEO Satellites

AbstractLow Earth Orbit satellites offer extensive data of the radiation belt region, but utilizing these observations is challenging due to potential contamination and difficulty of intercalibration with spacecraft measurements at Highly Elliptic Orbit that can observe all equatorial pitch‐angles. This study introduces a new intercalibration method for satellite measurements of energetic electrons in the radiation belts using a Data assimilation (DA) approach. We demonstrate our technique by intercalibrating the electron flux measurements of the National Oceanic and Atmospheric Administration (NOAA) Polar‐orbiting Operational Environmental Satellites (POES) NOAA‐15,‐16,‐17,‐18,‐19, and MetOp‐02 against Van Allen Probes observations from October 2012 to September 2013. We use a reanalysis of the radiation belts obtained by assimilating Van Allen Probes and Geostationary Operational Environmental Satellites observations into 3‐D Versatile Electron Radiation Belt (VERB‐3D) code simulations via a standard Kalman filter. We compare the reanalysis to the POES data set and estimate the flux ratios at each time, location, and energy. From these ratios, we derive energy and L* dependent recalibration coefficients. To validate our results, we analyze on‐orbit conjunctions between POES and Van Allen Probes. The conjunction recalibration coefficients and the data‐assimilative estimated coefficients show strong agreement, indicating that the differences between POES and Van Allen Probes observations remain within a factor of two. Additionally, the use of DA allows for improved statistics, as the possible comparisons are increased 10‐fold. Data‐assimilative intercalibration of satellite observations is an efficient approach that enables intercalibration of large data sets using short periods of data.

Multipoint Detection of GRB221009A’s Propagation through the Heliosphere

We present the results of processing the effects of the powerful gamma-ray burst GRB221009A captured by the charged particle detectors (electrostatic analyzers and solid-state detectors) on board spacecraft at different points in the heliosphere on 2022 October 9. To follow the GRB221009A propagation through the heliosphere, we used the electron and proton flux measurements from solar missions Solar Orbiter and STEREO-A; Earth’s magnetosphere and solar wind missions THEMIS and Wind; meteorological satellites POES15, POES19, and MetOp3; and MAVEN—a NASA mission orbiting Mars. GRB221009A had a structure of four bursts: the less intense Pulse 1—the triggering impulse—was detected by gamma-ray observatories at T 0 = 13:16:59 UT (near the Earth); the most intense Pulses 2 and 3 were detected on board all the spacecraft from the list; and Pulse 4 was detected in more than 500 s after Pulse 1. Due to their different scientific objectives, the spacecraft, whose data were used in this study, were separated by more than 1 au (Solar Orbiter and MAVEN). This enabled the tracking of GRB221009A as it was propagating across the heliosphere. STEREO-A was the first to register Pulse 2 and 3 of the GRB, almost 100 s before their detection by spacecraft in the vicinity of Earth. MAVEN detected GRB221009A Pulses 2, 3, and 4 at the orbit of Mars about 237 s after their detection near Earth. By processing the observed time delays, we show that the source location of the GRB221009A was at R.A. 288.°5, decl. 18.°5 ± 2° (J2000).

A Novel Electrodialysis Membrane, Modified by Polydopamine and Carbon Nanofibers, Removes Toxic Heavy Metal Ions From Wastewaters

Background: In light of severe and growing shortages of clean water and the rising environmental pollution in many countries, seawater desalination has been an effective method to produce freshwater. Cationic membranes have enabled environmental scientists to effectively remove toxic heavy metals from wastewater and to regenerate freshwater. Methods: We used a novel method, involving electro- and physico-chemical membranes to successfully remove toxic heavy metal ions (copper & chromium) from wastewater samples. Specifically, Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, surface wettability, flux, selectivity and electrical resistance measurements were applied to conduct this study. Results: The obtained results illustrated relatively uniform foaming of the modified membranes. Also, electron microscopic images indicated almost even distribution of the particles. The dada indicated that applying polydopamine layer and incorporating nanofibers in monomer solution caused surface hydrophilic enhancement. Also, increased carbon nanofibers loading ratio to 0.07% raised the ionic flux. The data also showed a higher capacity in the modified membranes for the removal of copper and chromium ions from the wastewater samples. Although the surface modified membranes displayed a higher flux and lower permselectivity to some extents, utilizing nanoparticles led to a steady trend of ion elimination. Generally, carbon nanofibers incorporation to the membrane surface modified samples up to 0.1% weight, resulting in nearly a constant areal electrical resistance. Conclusion: The novel method developed by this study is an excellent candidate with high potential for the removal of toxic heavy metal ions from wastewater samples.

Using MEPED observations to infer plasma density and chorus intensity in the radiation belts

Efforts to model and predict energetic electron fluxes in the radiation belts are highly sensitive to local wave-particle interactions. In this study, we use multi-point measurements of precipitating and trapped electron fluxes to investigate the dynamic variation of chorus wave-particle interactions during the 17 March 2013 storm. Quasilinear theory characterizes the chorus wave-particle interaction as a diffusive process, with the diffusion coefficients depending on the particle energy and pitch angle, as well as the background plasma parameters such as the wave intensity and plasma density. These plasma parameters in the radiation belts are spatially localized and time-varying, so we construct event-specific diffusion coefficients using MEPED (onboard POES/MetOp) measurements of electron fluxes at low Earth orbit. This new method provides realistic diffusion coefficients for chorus waves that account for changes in the wave intensity, the plasma density, and the magnetic field strength in the outer radiation belt. We show that the inferred chorus intensity is significantly lower than previous estimates that use MEPED observations since the same amount of increased precipitation by 30–300 keV electrons can be explained by a change in the plasma density. This technique therefore allows for us to create time varying, global maps of the plasma-gyrofrequency ratio (fpe/fce), and therefore plasma density, in the outer radiation belts using the MEPED measurements. The global density estimates compare reasonably well to in situ density measurements from RBSP-B.

Inter‐Calibration Between the Electron Flux Measurements of FengYun‐3B and Van Allen Probe‐A Based on Electron Phase Space Density Conjunctions

AbstractCross‐satellite calibration of energetic particle fluxes is essential to understanding Earth's radiation belt dynamics and modeling the space radiation environment. Using the method of comparing phase space density (PSD) conjunctions in the same set of phase space coordinates, we perform a cross‐satellite calibration of energetic electron fluxes measured by the Low Earth Orbit Chinese FengYun‐3B satellite (FY‐3B) and the near‐equatorial Highly Eccentric Orbit Van Allen Probe‐A (VAP‐A), respectively. VAP‐A provides pitch angle resolved electron (directional) differential fluxes while FY‐3B provides omnidirectional electron differential fluxes. Before calculating the PSDs from FY‐3B high energy electron detector (HEED), a method is introduced to estimate the local pitch angle of FY‐3B based on the installation direction information of HEED and the T89c magnetic field model. We calculate the calibration factors by using the PSD conjunctions inferred from the two satellites for three fixed sets of (μ, K, L*) during the geomagnetic storm times. The calibration factors range from 0.76 to 0.86 varying with fixed sets of (μ, K, L*), which indicates that the electron differential fluxes from FY‐3B are higher than that from VAP‐A. During geomagnetic quiet times, we perform calibration by using independent Gaussian fitting analysis of the number of points with the unaveraged PSDs of FY‐3B and VAP‐A for three fixed sets of (μ, K, L*), with the corresponding calibration factors of 0.78, 0.72, and 0.46. The calibrated electron differential fluxes of FY‐3B measured at the high magnetic latitudes, can be used in the future modeling of the radiation belt electron dynamics.

A statistical relationship between the fluence of magnetospheric relativistic electrons and interplanetary and geomagnetic characteristics

The correlation coefficients between the electron fluence, the solar wind speed and the geomagnetic activity Ap-index with different delay times are calculated. Calculations are based on measurements of magnetospheric electron fluxes with energy >2 MeV in geostationary orbits for 35 years (1987–2021).We use >2 MeV relativistic electron flux measurements from the different Energetic Particle Sensors (EPS) on the geosynchronous spacecrafts GOES. The correlation coefficients between electron fluences on neighboring days are calculated as well. There is significant inertia in the behavior of the fluence of high-energy magnetospheric electrons. It is found that the fluence of high-energy magnetospheric electrons is weakly related to the level of geomagnetic activity on the same day, but correlates with the geomagnetic activity Ap-index observed 2–3 days earlier. The fluence of high-energy magnetospheric electrons is quite closely related to the speed of the solar wind, especially with the speed measured 2 days earlier. In general, in cycles 22–24 of solar activity, higher correlation coefficients of the electron fluence with the solar wind speed and the Ap-index are observed in the phases of decline and minimum of solar activity. A three-parameter model has also been obtained based on the prehistory of the fluence behavior, data on the Ap-index of geomagnetic activity, and measurements of the solar wind speed. The created model allows to make the prediction of high-energy magnetospheric electrons fluence for the next day.The model shows good agreement with the experimental data with a high correlation coefficient (0.82) for the entire period 1987–2021.

Statistical investigation on equatorial pitch angle distribution of energetic electrons in Earth’s outer radiation belt during CME- and CIR-driven storms

We present a statistical investigation (September 2012 - September 2017) of pitch angle distribution (PAD) of energetic electrons (∼30 keV - 1 MeV) in the outer radiation belt (L ≥ 3) during CME- and CIR-driven geomagnetic storms using Van Allen Probe measurements. We selected geomagnetic storms based on minimum of SYM-H being less than -50 nT and classified the storms according to their drivers. Thus, we obtained 23 CME- and 24 CIR-driven storms. During the storm intervals, pitch angle resolved electron flux measurements are obtained from the MagEIS instrument on-board Van Allen Probe-A spacecraft. We assume symmetric pitch angle distributions around 90° pitch angle and fit the observed PADs with Legendre polynomials after propagating them to the magnetic equator. Legendre coefficients c2 and c4, and the ratio R = |c2/c4| are used to categorize the different PAD types. To resolve the spatio-temporal distribution of PADs, these coefficients are binned in 5 L-shell bins, 12 MLT bins for seven energy channels and four storm phases. We found that several hundreds of keV electrons exhibit clear dependence on local time, storm phases and storm drivers, with increased anisotropy for CME-driven storms during main and early recovery phases. On the contrary, we found that tens of keV electrons do not exhibit significant dependence on these parameters. We have discussed the different physical mechanisms responsible for the observed MLT dependent PADs and found drift-shell splitting to be the major contributor.

Average characteristics of high-energy magnetospheric electron flux enhancements and the parameters of near-Earth and interplanetary medium in 1987–2021

ABSTRACT Based on the data of 35-yr (1987–2021) measurements of magnetospheric electron fluxes with energy >2 MeV in geostationary orbits, solar wind speed, and geomagnetic activity, a catalogue of electron flux enhancements was compiled in which the electron fluence exceeds 108 cm–2 sr–1 d–1. The epoch superposition method performed using the GOES-13 spacecraft data shows that large electron flux enhancements are preceded by a significant increase in the solar wind velocity and the Ap index of geomagnetic activity, and immediately before the increase the relativistic electron flux decreases. For the events of the catalogue, the average characteristics of electron flux enhancements and parameters of the interplanetary and near-Earth medium were calculated: the mean values of the diurnal and total fluences during an event and the average duration of electron enhancements. The average duration of the electron flux enhancement is 5 d, and the maximum duration is 24 d. Based on the calculated mean values of the electron fluences, solar wind velocity, and Ap-index of geomagnetic activity on the day of electron enhancement and on previous days, a typical behaviour of these parameters during and before an electron flux enhancement was obtained. The average characteristics of electron flux enhancements and the parameters of interplanetary and near-Earth medium are calculated before large electron flux enhancements, when the fluence exceeds 3 × 108, 5 × 108, and 109 particles cm–2 sr–1 d–1, respectively. It is shown that the greater the increase in solar wind velocity and geomagnetic activity the larger the subsequent electron flux enhancement.

Characteristics of Electron Microburst Precipitation Based on High‐Resolution ELFIN Measurements

AbstractWe present statistical characteristics of electron microburst precipitation using high time‐resolution measurements from the low‐altitude Electron Losses and Fields InvestigatioN (ELFIN) CubeSats. The radial distribution of the equatorial projection of microbursts as a function of geomagnetic activity suggests that they are produced by resonant interaction with quasi‐parallel lower‐band chorus waves. ELFIN electron flux measurements provide the first statistical models of microburst energy spectra from 50 keV to 2 MeV. Microbursts with energies up to 150 keV have a relatively flat pitch‐angle spectrum. Estimates of scattering rates required to produce the observed flat spectra suggest that such precipitation signatures are due to near‐equatorial electron scattering by chorus wave packets with peak amplitudes of 0.4–0.9 nT, well above the threshold for nonlinear resonant interaction. More rare microbursts, exceeding 500 keV, are observed preferentially near dawn during disturbed periods. We interpret them as evidence of scattering by intense ducted chorus waves propagating from the equator up to middle latitudes with little attenuation.

A Study on Monte Carlo Simulation of the Radiation Environment above GeV at the DAMPE Orbit

The Dark Matter Particle Explorer (DAMPE) has been undergoing a stable on-orbit operation for more than 6 yr and acquired observations of over 11 billion events. A better understanding of the overall radiation environment of the DAMPE orbit is crucial for both simulation data production and flight data analysis. In this work, we study the radiation environment at low Earth orbit and develop a simulation software package using the framework of ATMNC3, in which state-of-the-art full 3D models of the Earth’s atmospheric and magnetic-field configurations are integrated. We consider in our Monte Carlo procedure event-by-event propagation of cosmic rays in the geomagnetic field and their interaction with the Earth’s atmosphere, focusing on the particles above GeV that are able to trigger the DAMPE data acquisition system. We compare the simulation results with the cosmic-ray electron and positron (CRE) flux measurements made by DAMPE. The overall agreement on both the spectral and angular distribution of the CRE flux demonstrates that our simulation is well established. Our software package could be of more general usage for simulation of the radiation environment of low Earth orbit at various altitudes.

A Statistical Examination of EMIC Wave‐Driven Electron Pitch Angle Scattering Signatures

AbstractElectromagnetic ion cyclotron (EMIC) waves have long been thought to contribute significantly to the variability of Earth's outer radiation belt because of their ability to scatter relativistic (>0.5 MeV) electrons into the loss cone on short timescales. We investigate statistically such pitch angle scattering signatures (“bite‐outs”) and their quantitative agreement with cold plasma theory. Our analysis is based on EMIC wave events and local plasma parameters observed simultaneously with energetic electrons by the Van Allen Probes between February and May 2017. We determine the energy and pitch angle ranges in which relativistic electron scattering is likely and find that, on average, EMIC wave‐driven scattering of core (E ≤ 2 MeV) electrons is possible in 28% of events. By comparing the expected ranges for scattering to electron flux measurements co‐located with the wave activity, we determine that scattering signatures are found in 46% of those. Additionally, we find that the scattering signatures are more likely to occur under increased geomagnetic activity and for waves with greater wave power. These results provide observational evidence that EMIC wave‐driven scattering of core relativistic electrons is common in the duskside outer radiation belt.