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Atmospheric waves
Authors: Thorne R M, Li W, Ma Q, Ni B, and Bortnik J
Title: Radiation belt electron acceleration by chorus waves during the 17 March 2013 storm
Abstract: Local acceleration driven by whistler-mode chorus waves is suggested to be fundamentally important for accelerating seed electron population to ultra-relativistic energies in the outer radiation belt. In this study, we quantitatively evaluate chorus-driven electron acceleration during the 17 March 2013 storm, when Van Allen Probes observed very rapid electron acceleration up to multi MeV within ∼15 hours. A clear peak in electron phase space density observed at L∗ ∼ 4 indicates that the internal local acceleration process was operating. We construct the global distribution of chorus wave intensity from the low-altitude electron measurements by multiple POES satellites over a broad L-MLT region, which is used to simulate the radiation belt electron dynamics driven by chorus waves. Our. . .
Date: 08/2014 Publisher: IEEE DOI: 10.1109/URSIGASS.2014.6929882 Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6929882
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banded whistler waves
Authors: Teng S., Tao X., and Li W
Title: Typical Characteristics of Whistler Mode Waves Categorized by Their Spectral Properties Using Van Allen Probes Observations
Abstract: Properties of banded, no‐gap, lower band only, and upper band only whistler mode waves (0.1–0.8fce) outside the plasmasphere are investigated using Van Allen Probes data. Our analysis shows that no‐gap whistler waves have higher occurrence rate at morning side and dayside, while banded and lower band only waves have higher occurrence rate between midnight and dawn. We also find that the occurrence rate of no‐gap whistler waves peaks at magnetic latitude |MLAT|∼8–10°, while banded waves have higher occurrence rate near the equator for urn:x-wiley:grl:media:grl58818:grl58818-math-0001°. The wave normal angle distributions of these four groups of waves are similar to previous results. The distinct local time and latitudinal distribution of no‐gap and banded whistler mode waves. . .
Date: 03/2019 Publisher: Geophysical Research Letters Pages: 3607 - 3614 DOI: 10.1029/2019GL082161 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL082161
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bandwidth
Authors: Gao X., Li W, Thorne R M, Bortnik J, Angelopoulos V, et al.
Title: Statistical results describing the bandwidth and coherence coefficient of whistler mode waves using THEMIS waveform data
Abstract: The bandwidths and coherence coefficients of lower band whistler mode waves are analyzed using Time History of Events and Macroscale Interactions during Substorms (THEMIS) waveform data for rising tones, falling tones, and hiss-like emissions separately. We also evaluate their dependences on the spatial location, electron density, the ratio of plasma frequency to local electron gyrofrequency (fpe/fce), and the wave amplitude. Our results show that the bandwidth normalized by the local electron gyrofrequency (fce) of rising and falling tones is very narrow (~0.01 fce), smaller than that of the hiss-like emissions (~0.025 fce). Meanwhile, the normalized bandwidth of discrete emissions gradually decreases with increasing wave amplitude, whereas that of hiss-like emissions increases slowly. Th. . .
Date: 11/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020158 Available at: http://doi.wiley.com/10.1002/2014JA020158
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beam instability
Authors: Li W, Mourenas D., Artemyev A. V., Bortnik J, Thorne R M, et al.
Title: Unraveling the excitation mechanisms of highly oblique lower band chorus waves
Abstract: Excitation mechanisms of highly oblique, quasi-electrostatic lower band chorus waves are investigated using Van Allen Probes observations near the equator of the Earth's magnetosphere. Linear growth rates are evaluated based on in situ, measured electron velocity distributions and plasma conditions and compared with simultaneously observed wave frequency spectra and wave normal angles. Accordingly, two distinct excitation mechanisms of highly oblique lower band chorus have been clearly identified for the first time. The first mechanism relies on cyclotron resonance with electrons possessing both a realistic temperature anisotropy at keV energies and a plateau at 100–500 eV in the parallel velocity distribution. The second mechanism corresponds to Landau resonance with a 100–500 eV . . .
Date: 09/2016 Publisher: Geophysical Research Letters Pages: 8867 - 8875 DOI: 10.1002/grl.v43.1710.1002/2016GL070386 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL070386/abstract
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Chorus
Authors: Li W, Chen L, Bortnik J, Thorne R M, Angelopoulos V, et al.
Title: First Evidence for Chorus at a Large Geocentric Distance as a Source of Plasmaspheric Hiss: Coordinated THEMIS and Van Allen Probes Observation
Abstract: Recent ray tracing suggests that plasmaspheric hiss can originate from chorus observed outside of the plasmapause. Although a few individual events have been reported to support this mechanism, the number of reported conjugate events is still very limited. Using coordinated observations between THEMIS and Van Allen Probes, we report on an interesting event, where chorus was observed at a large L-shell (~9.8), different from previously reported events at L < 6, but still exhibited a remarkable correlation with hiss observed in the outer plasmasphere (L ~ 5.5). Ray tracing indicates that a subset of chorus can propagate into the observed location of hiss on a timescale of ~ 5-6 s, in excellent agreement with the observed time lag between chorus and hiss. This provides quantitative support th. . .
Date: 01/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062832 Available at: http://doi.wiley.com/10.1002/2014GL062832
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Chorus wave
Authors: Li W, Thorne R M, Bortnik J, Baker D N, Reeves G D, et al.
Title: Solar wind conditions leading to efficient radiation belt electron acceleration: A superposed epoch analysis
Abstract: Determining preferential solar wind conditions leading to efficient radiation belt electron acceleration is crucial for predicting radiation belt electron dynamics. Using Van Allen Probes electron observations (>1 MeV) from 2012 to 2015, we identify a number of efficient and inefficient acceleration events separately to perform a superposed epoch analysis of the corresponding solar wind parameters and geomagnetic indices. By directly comparing efficient and inefficient acceleration events, we clearly show that prolonged southward Bz, high solar wind speed, and low dynamic pressure are critical for electron acceleration to >1 MeV energies in the heart of the outer radiation belt. We also evaluate chorus wave evolution using the superposed epoch analysis for the identified efficient and . . .
Date: 09/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL065342 Available at: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015GL065342/abstract
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Authors: Li W, Santolik O, Bortnik J, Thorne R M, Kletzing C A, et al.
Title: New Chorus Wave Properties Near the Equator from Van Allen Probes Wave Observations
Abstract: The chorus wave properties are evaluated using Van Allen Probes data in the Earth's equatorial magnetosphere. Two distinct modes of lower band chorus are identified: a quasi-parallel mode and a quasi-electrostatic mode, whose wave normal direction is close to the resonance cone. Statistical results indicate that the quasi-electrostatic (quasi-parallel) mode preferentially occurs during relatively quiet (disturbed) geomagnetic activity at lower (higher) L shells. Although the magnetic intensity of the quasi-electrostatic mode is considerably weaker than the quasi-parallel mode, their electric intensities are comparable. A newly identified feature of the quasi-electrostatic mode is that its frequency peaks at higher values compared to the quasi-parallel mode that exhibits a broad frequency s. . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL068780 Available at: http://doi.wiley.com/10.1002/2016GL068780
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chorus waves
Authors: Teng S., Tao X., and Li W
Title: Typical Characteristics of Whistler Mode Waves Categorized by Their Spectral Properties Using Van Allen Probes Observations
Abstract: Properties of banded, no‐gap, lower band only, and upper band only whistler mode waves (0.1–0.8fce) outside the plasmasphere are investigated using Van Allen Probes data. Our analysis shows that no‐gap whistler waves have higher occurrence rate at morning side and dayside, while banded and lower band only waves have higher occurrence rate between midnight and dawn. We also find that the occurrence rate of no‐gap whistler waves peaks at magnetic latitude |MLAT|∼8–10°, while banded waves have higher occurrence rate near the equator for urn:x-wiley:grl:media:grl58818:grl58818-math-0001°. The wave normal angle distributions of these four groups of waves are similar to previous results. The distinct local time and latitudinal distribution of no‐gap and banded whistler mode waves. . .
Date: 03/2019 Publisher: Geophysical Research Letters Pages: 3607 - 3614 DOI: 10.1029/2019GL082161 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL082161
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Authors: Li W, Mourenas D., Artemyev A., Agapitov O., Bortnik J, et al.
Title: Evidence of stronger pitch angle scattering loss caused by oblique whistler-mode waves as compared with quasi-parallel waves
Abstract: Wave normal distributions of lower-band whistler-mode waves observed outside the plasmapause exhibit two peaks; one near the parallel direction and the other at very oblique angles. We analyze a number of conjunction events between the Van Allen Probes near the equatorial plane and POES satellites at conjugate low altitudes, where lower-band whistler-mode wave amplitudes were inferred from the two-directional POES electron measurements over 30–100 keV, assuming that these waves were quasi-parallel. For conjunction events, the wave amplitudes inferred from the POES electron measurements were found to be overestimated as compared with the Van Allen Probes measurements primarily for oblique waves and quasi-parallel waves with small wave amplitudes (< ~20 pT) measured at low latitudes. This . . .
Date: 08/2014 Publisher: Geophysical Research Letters Pages: n/a - n/a DOI: 10.1002/2014GL061260 Available at: http://doi.wiley.com/10.1002/2014GL061260
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chorus-driven local acceleration
Authors: Li W, Ma Q, Thorne R M, Bortnik J, Zhang X.-J., et al.
Title: Radiation belt electron acceleration during the 17 March 2015 geomagnetic storm: Observations and simulations
Abstract: Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3-D diffusion simulation. By quantitatively comparing the observed and simulated electron evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak loca. . .
Date: 06/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 5520 - 5536 DOI: 10.1002/jgra.v121.610.1002/2016JA022400 Available at: http://doi.wiley.com/10.1002/2016JA022400
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CME
Authors: Kanekal S G, Baker D N, Henderson M G, Li W, Fennell J. F., et al.
Title: Relativistic electron response to the combined magnetospheric impact of a coronal mass ejection overlapping with a high-speed stream: Van Allen Probes observations
Abstract: During early November 2013, the magnetosphere experienced concurrent driving by a coronal mass ejection (CME) during an ongoing high-speed stream (HSS) event. The relativistic electron response to these two kinds of drivers, i.e., HSS and CME, is typically different, with the former often leading to a slower buildup of electrons at larger radial distances, while the latter energizing electrons rapidly with flux enhancements occurring closer to the Earth.We present a detailed analysis of the relativistic electron response including radial profiles of phase space density as observed by both MagEIS and REPT instruments on the Van Allen Probes mission. Data from the MagEIS instrument establishes the behavior of lower energy (<1MeV) electrons which span both intermediary and seed populations du. . .
Date: 09/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021395 Available at: http://doi.wiley.com/10.1002/2015JA021395
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coherence coefficient
Authors: Gao X., Li W, Thorne R M, Bortnik J, Angelopoulos V, et al.
Title: Statistical results describing the bandwidth and coherence coefficient of whistler mode waves using THEMIS waveform data
Abstract: The bandwidths and coherence coefficients of lower band whistler mode waves are analyzed using Time History of Events and Macroscale Interactions during Substorms (THEMIS) waveform data for rising tones, falling tones, and hiss-like emissions separately. We also evaluate their dependences on the spatial location, electron density, the ratio of plasma frequency to local electron gyrofrequency (fpe/fce), and the wave amplitude. Our results show that the bandwidth normalized by the local electron gyrofrequency (fce) of rising and falling tones is very narrow (~0.01 fce), smaller than that of the hiss-like emissions (~0.025 fce). Meanwhile, the normalized bandwidth of discrete emissions gradually decreases with increasing wave amplitude, whereas that of hiss-like emissions increases slowly. Th. . .
Date: 11/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020158 Available at: http://doi.wiley.com/10.1002/2014JA020158
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Drift shell splitting
Authors: Zhang X.-J., Li W, Thorne R M, Angelopoulos V, Ma Q, et al.
Title: Physical mechanism causing rapid changes in ultrarelativistic electron pitch angle distributions right after a shock arrival: Evaluation of an electron dropout event
Abstract: Three mechanisms have been proposed to explain relativistic electron flux depletions (dropouts) in the Earth's outer radiation belt during storm times: adiabatic expansion of electron drift shells due to a decrease in magnetic field strength, magnetopause shadowing and subsequent outward radial diffusion, and precipitation into the atmosphere (driven by EMIC wave scattering). Which mechanism predominates in causing electron dropouts commonly observed in the outer radiation belt is still debatable. In the present study, we evaluate the physical mechanism that may be primarily responsible for causing the sudden change in relativistic electron pitch angle distributions during a dropout event observed by Van Allen Probes during the main phase of the 27 February 2014 storm. During this event, t. . .
Date: 09/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022517 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA022517/abstract
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dropouts
Authors: Turner D. L., Angelopoulos V, Morley S. K., Henderson M G, Reeves G D, et al.
Title: On the cause and extent of outer radiation belt losses during the 30 September 2012 dropout event
Abstract: On 30 September 2012, a flux “dropout” occurred throughout Earth's outer electron radiation belt during the main phase of a strong geomagnetic storm. Using eight spacecraft from NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Van Allen Probes missions and NOAA's Geostationary Operational Environmental Satellites constellation, we examined the full extent and timescales of the dropout based on particle energy, equatorial pitch angle, radial distance, and species. We calculated phase space densities of relativistic electrons, in adiabatic invariant coordinates, which revealed that loss processes during the dropout were > 90% effective throughout the majority of the outer belt and the plasmapause played a key role in limiting the spatial extent . . .
Date: 03/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 1530 - 1540 DOI: 10.1002/2013JA019446 Available at: http://doi.wiley.com/10.1002/2013JA019446
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Authors: Zhang X.-J., Li W, Thorne R M, Angelopoulos V, Ma Q, et al.
Title: Physical mechanism causing rapid changes in ultrarelativistic electron pitch angle distributions right after a shock arrival: Evaluation of an electron dropout event
Abstract: Three mechanisms have been proposed to explain relativistic electron flux depletions (dropouts) in the Earth's outer radiation belt during storm times: adiabatic expansion of electron drift shells due to a decrease in magnetic field strength, magnetopause shadowing and subsequent outward radial diffusion, and precipitation into the atmosphere (driven by EMIC wave scattering). Which mechanism predominates in causing electron dropouts commonly observed in the outer radiation belt is still debatable. In the present study, we evaluate the physical mechanism that may be primarily responsible for causing the sudden change in relativistic electron pitch angle distributions during a dropout event observed by Van Allen Probes during the main phase of the 27 February 2014 storm. During this event, t. . .
Date: 09/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022517 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA022517/abstract
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electromagnetic ion cyclotron waves
Authors: Ma Q, Li W, Yue C., Thorne R M, Bortnik J, et al.
Title: Ion Heating by Electromagnetic Ion Cyclotron Waves and Magnetosonic Waves in the Earth's Inner Magnetosphere
Abstract: Electromagnetic ion cyclotron (EMIC) waves and magnetosonic waves are commonly observed in the Earth's magnetosphere associated with enhanced ring current activity. Using wave and ion measurements from the Van Allen Probes, we identify clear correlations between the hydrogen‐ and helium‐band EMIC waves with the enhancement of trapped helium and oxygen ion fluxes, respectively. We calculate the diffusion coefficients of different ion species using quasi‐linear theory to understand the effects of resonant scattering by EMIC waves. Our calculations indicate that EMIC waves can cause pitch angle scattering loss of several keV to hundreds of keV ions, and heating of tens of eV to several keV helium and oxygen ions by hydrogen‐ and helium‐band EMIC waves, respectively. Moreover, we fou. . .
Date: 06/2019 Publisher: Geophysical Research Letters Pages: 6258 - 6267 DOI: 10.1029/2019GL083513 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL083513
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Electron acceleration
Authors: Li W, Thorne R M, Bortnik J, Baker D N, Reeves G D, et al.
Title: Solar wind conditions leading to efficient radiation belt electron acceleration: A superposed epoch analysis
Abstract: Determining preferential solar wind conditions leading to efficient radiation belt electron acceleration is crucial for predicting radiation belt electron dynamics. Using Van Allen Probes electron observations (>1 MeV) from 2012 to 2015, we identify a number of efficient and inefficient acceleration events separately to perform a superposed epoch analysis of the corresponding solar wind parameters and geomagnetic indices. By directly comparing efficient and inefficient acceleration events, we clearly show that prolonged southward Bz, high solar wind speed, and low dynamic pressure are critical for electron acceleration to >1 MeV energies in the heart of the outer radiation belt. We also evaluate chorus wave evolution using the superposed epoch analysis for the identified efficient and . . .
Date: 09/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL065342 Available at: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015GL065342/abstract
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Authors: Li W, Ma Q, Thorne R M, Bortnik J, Zhang X.-J., et al.
Title: Radiation belt electron acceleration during the 17 March 2015 geomagnetic storm: Observations and simulations
Abstract: Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3-D diffusion simulation. By quantitatively comparing the observed and simulated electron evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak loca. . .
Date: 06/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 5520 - 5536 DOI: 10.1002/jgra.v121.610.1002/2016JA022400 Available at: http://doi.wiley.com/10.1002/2016JA022400
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electron acceleration and loss
Authors: Ma Q, Li W, Thorne R M, Nishimura Y., Zhang X.-J., et al.
Title: Simulation of energy-dependent electron diffusion processes in the Earth's outer radiation belt
Abstract: The radial and local diffusion processes induced by various plasma waves govern the highly energetic electron dynamics in the Earth's radiation belts, causing distinct characteristics in electron distributions at various energies. In this study, we present our simulation results of the energetic electron evolution during a geomagnetic storm using the University of California, Los Angeles 3-D diffusion code. Following the plasma sheet electron injections, the electrons at different energy bands detected by the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron Proton Telescope (REPT) instruments on board the Van Allen Probes exhibit a rapid enhancement followed by a slow diffusive movement in differential energy fluxes, and the radial extent to which electrons can penetra. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022507 Available at: http://doi.wiley.com/10.1002/2016JA022507
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electron accelerationl whistler mode waves
Authors: Ma Q, Li W, Bortnik J, Thorne R M, Chu X., et al.
Title: Quantitative Evaluation of Radial Diffusion and Local Acceleration Processes During GEM Challenge Events
Abstract: We simulate the radiation belt electron flux enhancements during selected Geospace Environment Modeling (GEM) challenge events to quantitatively compare the major processes involved in relativistic electron acceleration under different conditions. Van Allen Probes observed significant electron flux enhancement during both the storm time of 17–18 March 2013 and non–storm time of 19–20 September 2013, but the distributions of plasma waves and energetic electrons for the two events were dramatically different. During 17–18 March 2013, the SYM‐H minimum reached −130 nT, intense chorus waves (peak Bw ~140 pT) occurred at 3.5 < L < 5.5, and several hundred keV to several MeV electron fluxes increased by ~2 orders of magnitude mostly at 3.5 < L < 5.5. During 19–20 September 2013, th. . .
Date: 03/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA025114 Available at: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JA025114
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electron distribution
Authors: Mourenas D., Artemyev A. V., Agapitov O.V., Krasnoselskikh V., and Li W
Title: Approximate analytical solutions for the trapped electron distribution due to quasi-linear diffusion by whistler-mode waves
Abstract: The distribution of trapped energetic electrons inside the Earth's radiation belts is the focus of intense studies aiming at better describing the evolution of the space environment in the presence of various disturbances induced by the solar wind or by an enhanced lightning activity. Such studies are usually performed by means of comparisons with full numerical simulations solving the Fokker-Planck quasi-linear diffusion equation for the particle distribution function. Here, we present for the first time approximate but realistic analytical solutions for the electron distribution, which are shown to be in good agreement with exact numerical solutions in situations where resonant scattering of energetic electrons by whistler-mode hiss, lightning-generated or chorus waves, is the dominant p. . .
Date: 11/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020443 Available at: http://doi.wiley.com/10.1002/2014JA020443
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electron flux decay
Authors: Ma Q, Li W, Thorne R M, Bortnik J, Reeves G D, et al.
Title: Characteristic energy range of electron scattering due to plasmaspheric hiss
Abstract: We investigate the characteristic energy range of electron flux decay due to the interaction with plasmaspheric hiss in the Earth's inner magnetosphere. The Van Allen Probes have measured the energetic electron flux decay profiles in the Earth's outer radiation belt during a quiet period following the geomagnetic storm that occurred on 7 November 2015. The observed energy of significant electron decay increases with decreasing L shell and is well correlated with the energy band corresponding to the first adiabatic invariant μ = 4–200 MeV/G. The electron diffusion coefficients due to hiss scattering are calculated at L = 2–6, and the modeled energy band of effective pitch angle scattering is also well correlated with the constant μ lines and is consistent with the observed e. . .
Date: 11/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023311 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023311/full
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electron precipitation
Authors: Li W, Mourenas D., Artemyev A., Agapitov O., Bortnik J, et al.
Title: Evidence of stronger pitch angle scattering loss caused by oblique whistler-mode waves as compared with quasi-parallel waves
Abstract: Wave normal distributions of lower-band whistler-mode waves observed outside the plasmapause exhibit two peaks; one near the parallel direction and the other at very oblique angles. We analyze a number of conjunction events between the Van Allen Probes near the equatorial plane and POES satellites at conjugate low altitudes, where lower-band whistler-mode wave amplitudes were inferred from the two-directional POES electron measurements over 30–100 keV, assuming that these waves were quasi-parallel. For conjunction events, the wave amplitudes inferred from the POES electron measurements were found to be overestimated as compared with the Van Allen Probes measurements primarily for oblique waves and quasi-parallel waves with small wave amplitudes (< ~20 pT) measured at low latitudes. This . . .
Date: 08/2014 Publisher: Geophysical Research Letters Pages: n/a - n/a DOI: 10.1002/2014GL061260 Available at: http://doi.wiley.com/10.1002/2014GL061260
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Authors: Capannolo L., Li W, Ma Q, Chen L, Shen X.‐C., et al.
Title: Direct Observation of Subrelativistic Electron Precipitation Potentially Driven by EMIC Waves
Abstract: Electromagnetic 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 . . .
Date: 11/2019 Publisher: Geophysical Research Letters DOI: 10.1029/2019GL084202 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL084202
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Authors: Li W, Shen X.‐C., Ma Q, Capannolo L., Shi R., et al.
Title: Quantification of Energetic Electron Precipitation Driven by Plume Whistler Mode Waves, Plasmaspheric Hiss, and Exohiss
Abstract: Whistler mode waves are important for precipitating energetic electrons into Earth's upper atmosphere, while the quantitative effect of each type of whistler mode wave on electron precipitation is not well understood. In this letter, we evaluate energetic electron precipitation driven by three types of whistler mode waves: plume whistler mode waves, plasmaspheric hiss, and exohiss observed outside the plasmapause. By quantitatively analyzing three conjunction events between Van Allen Probes and POES/MetOp satellites, together with quasi‐linear calculation, we found that plume whistler mode waves are most effective in pitch angle scattering loss, particularly for the electrons from tens to hundreds of keV. Our new finding provides the first direct evidence of effective pitch angle scatter. . .
Date: 03/2019 Publisher: Geophysical Research Letters Pages: 3615 - 3624 DOI: 10.1029/2019GL082095 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL082095
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Authors: Zhang X.-J., Li W, Ma Q, Thorne R M, Angelopoulos V, et al.
Title: Direct evidence for EMIC wave scattering of relativistic electrons in space
Abstract: Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes. EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022521 Available at: http://doi.wiley.com/10.1002/2016JA022521
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Electron transport
Authors: Ma Q, Li W, Thorne R M, Bortnik J, Reeves G D, et al.
Title: Diffusive transport of several hundred keV electrons in the Earth's slot region
Abstract: We investigate the gradual diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward diffusion and decay of ~200-600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10-day non-disturbed period following the storm, the peak of electron fluxes gradually moved from L~2.7 to L~2.4, and the flux levels decreased by a factor of ~2-4 depending on the electron energy. We simulated the radial intrusion and decay of electrons using a 3-dimentional diffusion code, which reproduced the energy-dependent transport of electrons from ~100 keV to 1 MeV in the slot region. At energies of 100-200 keV, the electrons experience fast transport across the slot region due to the . . .
Date: 09/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024452 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024452/full
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Electron traps
Authors: Li W, Ni B, Thorne R M, Bortnik J, Green J C, et al.
Title: Calculation of whistler-mode wave intensity using energetic electron precipitation
Abstract: The energetic electron population measured by multiple low-altitude POES satellites is used to infer whistlermode wave amplitudes using a physics-based inversion technique. We validate this technique by quantitatively analyzing a conjunction event between the Van Allen Probes and POES, and find that the inferred hiss wave amplitudes from POES electron measurements agree remarkably well with directly measured hiss waves amplitudes. We also use this technique to construct the global distribution of chorus wave intensity with extensive coverage over a broad L-MLT region during the 8–9 October 2012 storm and demonstrate that the inferred chorus wave amplitudes agree well with conjugate measurements of chorus wave amplitudes from the Van Allen Probes. The evolution of the whistler-mode wave i. . .
Date: 08/2014 Publisher: IEEE DOI: 10.1109/URSIGASS.2014.6929965 Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6929965
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EMIC wave occurrence
Authors: Min Kyungguk, Lee Jeongwoo, Keika Kunihiro, and Li W
Title: Global distribution of EMIC waves derived from THEMIS observations
Abstract: [1] Electromagnetic ion cyclotron (EMIC) waves play an important role in magnetospheric dynamics and their global distribution has been of great interest. This paper presents the distribution of EMIC waves over a broader range than ever before, as enabled by observations with the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft from 2007 to 2010. Our major findings are: (1) There are two major peaks in the EMIC wave occurrence probability. One is at dusk and 8–12 RE where the helium band dominates the hydrogen band waves. The other is at dawn and 10–12 RE where the hydrogen band dominates the helium band waves. (2) In terms of wave spectral power the dusk events are stronger (≈10 nT2/Hz) than the dawn events (≈3 nT2/Hz). (3) The dawn . . .
Date: 05/2012 Publisher: Journal of Geophysical Research DOI: 10.1029/2012JA017515
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EMIC waves
Authors: Capannolo L., Li W, Ma Q, Chen L, Shen X.‐C., et al.
Title: Direct Observation of Subrelativistic Electron Precipitation Potentially Driven by EMIC Waves
Abstract: Electromagnetic 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 . . .
Date: 11/2019 Publisher: Geophysical Research Letters DOI: 10.1029/2019GL084202 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL084202
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Authors: Capannolo L., Li W, Ma Q, Shen X.‐C., Zhang X.‐J., et al.
Title: Energetic Electron Precipitation: Multievent Analysis of Its Spatial Extent During EMIC Wave Activity
Abstract: Electromagnetic ion cyclotron (EMIC) waves can drive precipitation of tens of keV protons and relativistic electrons, and are a potential candidate for causing radiation belt flux dropouts. In this study, we quantitatively analyze three cases of EMIC‐driven precipitation, which occurred near the dusk sector observed by multiple Low‐Earth‐Orbiting (LEO) Polar Operational Environmental Satellites/Meteorological Operational satellite programme (POES/MetOp) satellites. During EMIC wave activity, the proton precipitation occurred from few tens of keV up to hundreds of keV, while the electron precipitation was mainly at relativistic energies. We compare observations of electron precipitation with calculations using quasi‐linear theory. For all cases, we consider the effects of other magn. . .
Date: 03/2019 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA026291 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA026291
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Authors: Zhang X.-J., Li W, Ma Q, Thorne R M, Angelopoulos V, et al.
Title: Direct evidence for EMIC wave scattering of relativistic electrons in space
Abstract: Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes. EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022521 Available at: http://doi.wiley.com/10.1002/2016JA022521
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Authors: Min Kyungguk, Lee Jeongwoo, Keika Kunihiro, and Li W
Title: Global distribution of EMIC waves derived from THEMIS observations
Abstract: [1] Electromagnetic ion cyclotron (EMIC) waves play an important role in magnetospheric dynamics and their global distribution has been of great interest. This paper presents the distribution of EMIC waves over a broader range than ever before, as enabled by observations with the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft from 2007 to 2010. Our major findings are: (1) There are two major peaks in the EMIC wave occurrence probability. One is at dusk and 8–12 RE where the helium band dominates the hydrogen band waves. The other is at dawn and 10–12 RE where the hydrogen band dominates the helium band waves. (2) In terms of wave spectral power the dusk events are stronger (≈10 nT2/Hz) than the dawn events (≈3 nT2/Hz). (3) The dawn . . .
Date: 05/2012 Publisher: Journal of Geophysical Research DOI: 10.1029/2012JA017515
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Authors: Zhang X.-J., Li W, Thorne R M, Angelopoulos V, Bortnik J, et al.
Title: Statistical distribution of EMIC wave spectra: Observations from Van Allen Probes
Abstract: It has been known that electromagnetic ion cyclotron (EMIC) waves can precipitate ultrarelativistic electrons through cyclotron resonant scattering. However, the overall effectiveness of this mechanism has yet to be quantified, because it is difficult to obtain the global distribution of EMIC waves that usually exhibit limited spatial presence. We construct a statistical distribution of EMIC wave frequency spectra and their intensities based on Van Allen Probes measurements from September 2012 to December 2015. Our results show that as the ratio of plasma frequency over electron gyrofrequency increases, EMIC wave power becomes progressively dominated by the helium band. There is a pronounced dawn-dusk asymmetry in the wave amplitude and the frequency spectrum. The frequency spectrum does n. . .
Date: 12/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL071158 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL071158/full
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Authors: Capannolo L., Li W, Ma Q, Zhang X.-J., Redmon R. J., et al.
Title: Understanding the Driver of Energetic Electron Precipitation Using Coordinated Multisatellite Measurements
Abstract: Magnetospheric plasma waves play a significant role in ring current and radiation belt dynamics, leading to pitch angle scattering loss and/or stochastic acceleration of the particles. During a non‐storm time dropout event on 24 September 2013, intense electromagnetic ion cyclotron (EMIC) waves were detected by Van Allen Probe A (Radiation Belt Storm Probes‐A). We quantitatively analyze a conjunction event when Van Allen Probe A was located approximately along the same magnetic field line as MetOp‐01, which detected simultaneous precipitation of >30 keV protons and energetic electrons over an unexpectedly broad energy range (>~30 keV). Multipoint observations together with quasi‐linear theory provide direct evidence that the observed electron precipitation at higher energy (>~700 k. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078604 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078604
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Authors: Nishimura Y., Bortnik J, Li W, Lyons L R, Donovan E. F., et al.
Title: Evolution of nightside subauroral proton aurora caused by transient plasma sheet flows
Abstract: While nightside subauroral proton aurora shows rapid temporal variations, the cause of this variability has rarely been investigated. Using well-coordinated observations by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imagers, THEMIS satellites in the equatorial magnetosphere, and the low-altitude NOAA 17 satellite, we examined the rapid temporal evolution of subauroral proton aurora in the premidnight sector. An isolated proton aurora occurred soon after an auroral poleward boundary intensification that was followed by an auroral streamer reaching the equatorward boundary of the auroral oval. Three THEMIS satellites in the magnetotail detected flow bursts and one of the THEMIS satellites in the outer plasmasphere observed a ring current injectio. . .
Date: 07/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 5295 - 5304 DOI: 10.1002/2014JA020029 Available at: http://doi.wiley.com/10.1002/2014JA020029
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Empirical Fitting
Authors: Ma Q, Li W, Bortnik J, Kletzing C A, Kurth W S, et al.
Title: Global Survey and Empirical Model of Fast Magnetosonic Waves Over Their Full Frequency Range in Earth's Inner Magnetosphere
Abstract: We investigate the global distribution and provide empirical models of fast magnetosonic waves using the combined observations by the magnetometer and waveform receiver on board Van Allen Probes. The magnetometer measurements of magnetosonic waves indicate a significant wave power within the frequency range from the helium gyrofrequency to 20 Hz at L ≥ 4 in the afternoon sector, both inside and outside the plasmapause. The waveform receiver measurements indicate a significant wave power from 20 Hz to the lower hybrid resonance frequency at L ≤ 5.5 near the dayside outside the plasmapause or in the afternoon sector inside the plasmapause. The sum of the wave powers from the two instruments provides the wave power distribution over the complete frequency range. The most significant root. . .
Date: 12/2019 Publisher: Journal of Geophysical Research: Space Physics Pages: 10270 - 10282 DOI: 10.1029/2019JA027407 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JA027407
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Energetic electron diffusion
Authors: Ma Q, Li W, Thorne R M, Bortnik J, Reeves G D, et al.
Title: Diffusive transport of several hundred keV electrons in the Earth's slot region
Abstract: We investigate the gradual diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward diffusion and decay of ~200-600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10-day non-disturbed period following the storm, the peak of electron fluxes gradually moved from L~2.7 to L~2.4, and the flux levels decreased by a factor of ~2-4 depending on the electron energy. We simulated the radial intrusion and decay of electrons using a 3-dimentional diffusion code, which reproduced the energy-dependent transport of electrons from ~100 keV to 1 MeV in the slot region. At energies of 100-200 keV, the electrons experience fast transport across the slot region due to the . . .
Date: 09/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024452 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024452/full
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energetic electron precipitation
Authors: Capannolo L., Li W, Ma Q, Shen X.‐C., Zhang X.‐J., et al.
Title: Energetic Electron Precipitation: Multievent Analysis of Its Spatial Extent During EMIC Wave Activity
Abstract: Electromagnetic ion cyclotron (EMIC) waves can drive precipitation of tens of keV protons and relativistic electrons, and are a potential candidate for causing radiation belt flux dropouts. In this study, we quantitatively analyze three cases of EMIC‐driven precipitation, which occurred near the dusk sector observed by multiple Low‐Earth‐Orbiting (LEO) Polar Operational Environmental Satellites/Meteorological Operational satellite programme (POES/MetOp) satellites. During EMIC wave activity, the proton precipitation occurred from few tens of keV up to hundreds of keV, while the electron precipitation was mainly at relativistic energies. We compare observations of electron precipitation with calculations using quasi‐linear theory. For all cases, we consider the effects of other magn. . .
Date: 03/2019 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA026291 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA026291
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energetic particle injections
Authors: Turner D. L., Claudepierre S G, Fennell J. F., O'Brien T P, Blake J B, et al.
Title: Energetic electron injections deep into the inner magnetosphere associated with substorm activity
Abstract: From a survey of the first nightside season of NASA's Van Allen Probes mission (Dec/2012 – Sep/2013), 47 energetic (10s to 100s of keV) electron injection events were found at L-shells ≤ 4, all of which are deeper than any previously reported substorm-related injections. Preliminary details from these events are presented, including how: all occurred shortly after dipolarization signatures and injections were observed at higher L-shells; the deepest observed injection was at L~2.5; and, surprisingly, L≤4 injections are limited in energy to ≤250 keV. We present a detailed case study of one example event revealing that the injection of electrons down to L~3.5 was different from injections observed at higher L and likely resulted from drift resonance with a fast magnetosonic wave in t. . .
Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL063225 Available at: http://doi.wiley.com/10.1002/2015GL063225
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energetic particle precipitation
Authors: Capannolo L., Li W, Ma Q, Zhang X.-J., Redmon R. J., et al.
Title: Understanding the Driver of Energetic Electron Precipitation Using Coordinated Multisatellite Measurements
Abstract: Magnetospheric plasma waves play a significant role in ring current and radiation belt dynamics, leading to pitch angle scattering loss and/or stochastic acceleration of the particles. During a non‐storm time dropout event on 24 September 2013, intense electromagnetic ion cyclotron (EMIC) waves were detected by Van Allen Probe A (Radiation Belt Storm Probes‐A). We quantitatively analyze a conjunction event when Van Allen Probe A was located approximately along the same magnetic field line as MetOp‐01, which detected simultaneous precipitation of >30 keV protons and energetic electrons over an unexpectedly broad energy range (>~30 keV). Multipoint observations together with quasi‐linear theory provide direct evidence that the observed electron precipitation at higher energy (>~700 k. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078604 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078604
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Energy measurement
Authors: Li W, Ni B, Thorne R M, Bortnik J, Green J C, et al.
Title: Calculation of whistler-mode wave intensity using energetic electron precipitation
Abstract: The energetic electron population measured by multiple low-altitude POES satellites is used to infer whistlermode wave amplitudes using a physics-based inversion technique. We validate this technique by quantitatively analyzing a conjunction event between the Van Allen Probes and POES, and find that the inferred hiss wave amplitudes from POES electron measurements agree remarkably well with directly measured hiss waves amplitudes. We also use this technique to construct the global distribution of chorus wave intensity with extensive coverage over a broad L-MLT region during the 8–9 October 2012 storm and demonstrate that the inferred chorus wave amplitudes agree well with conjugate measurements of chorus wave amplitudes from the Van Allen Probes. The evolution of the whistler-mode wave i. . .
Date: 08/2014 Publisher: IEEE DOI: 10.1109/URSIGASS.2014.6929965 Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6929965
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energy-dependent diffusion
Authors: Ma Q, Li W, Thorne R M, Nishimura Y., Zhang X.-J., et al.
Title: Simulation of energy-dependent electron diffusion processes in the Earth's outer radiation belt
Abstract: The radial and local diffusion processes induced by various plasma waves govern the highly energetic electron dynamics in the Earth's radiation belts, causing distinct characteristics in electron distributions at various energies. In this study, we present our simulation results of the energetic electron evolution during a geomagnetic storm using the University of California, Los Angeles 3-D diffusion code. Following the plasma sheet electron injections, the electrons at different energy bands detected by the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron Proton Telescope (REPT) instruments on board the Van Allen Probes exhibit a rapid enhancement followed by a slow diffusive movement in differential energy fluxes, and the radial extent to which electrons can penetra. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022507 Available at: http://doi.wiley.com/10.1002/2016JA022507
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equatorial pitch angle distribution
Authors: Zhang X.-J., Li W, Ma Q, Thorne R M, Angelopoulos V, et al.
Title: Direct evidence for EMIC wave scattering of relativistic electrons in space
Abstract: Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes. EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022521 Available at: http://doi.wiley.com/10.1002/2016JA022521
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FIREBIRD‐II
Authors: Capannolo L., Li W, Ma Q, Chen L, Shen X.‐C., et al.
Title: Direct Observation of Subrelativistic Electron Precipitation Potentially Driven by EMIC Waves
Abstract: Electromagnetic 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 . . .
Date: 11/2019 Publisher: Geophysical Research Letters DOI: 10.1029/2019GL084202 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL084202
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Fokker-Planck equation
Authors: Zhang X.-J., Li W, Ma Q, Thorne R M, Angelopoulos V, et al.
Title: Direct evidence for EMIC wave scattering of relativistic electrons in space
Abstract: Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes. EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022521 Available at: http://doi.wiley.com/10.1002/2016JA022521
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Global Survey
Authors: Ma Q, Li W, Bortnik J, Kletzing C A, Kurth W S, et al.
Title: Global Survey and Empirical Model of Fast Magnetosonic Waves Over Their Full Frequency Range in Earth's Inner Magnetosphere
Abstract: We investigate the global distribution and provide empirical models of fast magnetosonic waves using the combined observations by the magnetometer and waveform receiver on board Van Allen Probes. The magnetometer measurements of magnetosonic waves indicate a significant wave power within the frequency range from the helium gyrofrequency to 20 Hz at L ≥ 4 in the afternoon sector, both inside and outside the plasmapause. The waveform receiver measurements indicate a significant wave power from 20 Hz to the lower hybrid resonance frequency at L ≤ 5.5 near the dayside outside the plasmapause or in the afternoon sector inside the plasmapause. The sum of the wave powers from the two instruments provides the wave power distribution over the complete frequency range. The most significant root. . .
Date: 12/2019 Publisher: Journal of Geophysical Research: Space Physics Pages: 10270 - 10282 DOI: 10.1029/2019JA027407 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JA027407
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hiss
Authors: Li W, Chen L, Bortnik J, Thorne R M, Angelopoulos V, et al.
Title: First Evidence for Chorus at a Large Geocentric Distance as a Source of Plasmaspheric Hiss: Coordinated THEMIS and Van Allen Probes Observation
Abstract: Recent ray tracing suggests that plasmaspheric hiss can originate from chorus observed outside of the plasmapause. Although a few individual events have been reported to support this mechanism, the number of reported conjugate events is still very limited. Using coordinated observations between THEMIS and Van Allen Probes, we report on an interesting event, where chorus was observed at a large L-shell (~9.8), different from previously reported events at L < 6, but still exhibited a remarkable correlation with hiss observed in the outer plasmasphere (L ~ 5.5). Ray tracing indicates that a subset of chorus can propagate into the observed location of hiss on a timescale of ~ 5-6 s, in excellent agreement with the observed time lag between chorus and hiss. This provides quantitative support th. . .
Date: 01/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062832 Available at: http://doi.wiley.com/10.1002/2014GL062832
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Authors: Li W, Shen X.‐C., Ma Q, Capannolo L., Shi R., et al.
Title: Quantification of Energetic Electron Precipitation Driven by Plume Whistler Mode Waves, Plasmaspheric Hiss, and Exohiss
Abstract: Whistler mode waves are important for precipitating energetic electrons into Earth's upper atmosphere, while the quantitative effect of each type of whistler mode wave on electron precipitation is not well understood. In this letter, we evaluate energetic electron precipitation driven by three types of whistler mode waves: plume whistler mode waves, plasmaspheric hiss, and exohiss observed outside the plasmapause. By quantitatively analyzing three conjunction events between Van Allen Probes and POES/MetOp satellites, together with quasi‐linear calculation, we found that plume whistler mode waves are most effective in pitch angle scattering loss, particularly for the electrons from tens to hundreds of keV. Our new finding provides the first direct evidence of effective pitch angle scatter. . .
Date: 03/2019 Publisher: Geophysical Research Letters Pages: 3615 - 3624 DOI: 10.1029/2019GL082095 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL082095
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hiss diffusion coefficient
Authors: Li W, Ma Q, Thorne R M, Bortnik J, Kletzing C A, et al.
Title: Statistical properties of plasmaspheric hiss derived from Van Allen Probes data and their Effects on radiation belt electron dynamics
Abstract: Plasmaspheric hiss is known to play an important role in controlling the overall structure and dynamics of radiation belt electrons inside the plasmasphere. Using newly available Van Allen Probes wave data, which provide excellent coverage in the entire inner magnetosphere, we evaluate the global distribution of the hiss wave frequency spectrum and wave intensity for different levels of substorm activity. Our statistical results show that observed hiss peak frequencies are generally lower than the commonly adopted value (~550 Hz), which was in frequent use, and that the hiss wave power frequently extends below 100 Hz, particularly at larger L shells (> ~3) on the dayside during enhanced levels of substorm activity. We also compare electron pitch angle scattering rates caused by hiss . . .
Date: 05/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021048 Available at: http://doi.wiley.com/10.1002/2015JA021048
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