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Alfven waves
Authors: Chaston C. C., Bonnell J. W., Wygant J R, Reeves G D, Baker D N, et al.
Title: Radial transport of radiation belt electrons in kinetic field-line resonances
Abstract: A representative case study from the Van Allen Probes during a geomagnetic storm recovery phase reveals enhanced electron fluxes at intermediate pitch angles over energies from ~100 keV to 5 MeV coincident with broadband low frequency electromagnetic waves. The statistical properties of these waves are used to build a model for radial diffusion via drift-bounce resonances in kinetic Alfvén eigenmodes/kinetic field-line resonances. Estimated diffusion coefficients indicate timescales for radial transport of the order of hours in storm-time events at energies from <100 keV to MeVs over equatorial pitch angles from the edge of the loss cone to nearly perpendicular to the geomagnetic field. The correlation of kinetic resonances with electron depletions and enhancements during storm main phase. . .
Date: 07/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074587 Available at: onlinelibrary.wiley.com/doi/10.1002/2017GL074587/full
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Authors: Chaston C. C., Bonnell J. W., Wygant J R, Kletzing C A, Reeves G D, et al.
Title: Extreme ionospheric ion energization and electron heating in Alfvén waves in the storm-time inner magnetosphere
Abstract: We report measurements of energized outflowing/bouncing ionospheric ions and heated electrons in the inner magnetosphere during a geomagnetic storm. The ions arrive in the equatorial plane with pitch angles that increase with energy over a range from tens of eV to > 50 keV while the electrons are field-aligned up to ~1 keV. These particle distributions are observed during intervals of broadband low frequency electromagnetic field fluctuations consistent with a Doppler-shifted spectrum of kinetic Alfvén waves and kinetic field-line resonances. The fluctuations extend from L≈3 out to the apogee of the Van Allen Probes spacecraft at L≈6.5. They thereby span most of the L-shell range occupied by the ring current. These measurements suggest a model for ionospheric ion outflow and energizat. . .
Date: 12/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL066674 Available at: http://doi.wiley.com/10.1002/2015GL066674http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015GL066674
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Authors: Chaston C. C., Bonnell J. W., Kletzing C A, Hospodarsky G B, Wygant J R, et al.
Title: Broadband low frequency electromagnetic waves in the inner magnetosphere
Abstract: A prominent yet largely unrecognized feature of the inner magnetosphere associated with particle injections, and more generally geomagnetic storms, is the occurrence of broadband electromagnetic field fluctuations over spacecraft frame frequencies (fsc) extending from effectively zero to fsc ≳ 100 Hz. Using observations from the Van Allen Probes we show that these waves most commonly occur pre-midnight but are observed over a range of local times extending into the dayside magnetosphere. We find that the variation of magnetic spectral energy density with fsc obeys inline image over several decades with a spectral break-point at fb ≈1 Hz. The values for α are log normally distributed with α = 1.9 ± 0.6 for fsc < fb andα = 2.9 ± 0.6 for fsc > fb. A is . . .
Date: 09/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021690 Available at: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015JA021690/abstract
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Authors: Chaston C. C., Bonnell J. W., Halford A J, Reeves G D, Baker D N, et al.
Title: Pitch Angle Scattering and Loss of Radiation Belt Electrons in Broadband Electromagnetic Waves
Abstract: A magnetic conjunction between Van Allen Probes spacecraft and the Balloon Array for Radiation‐belt Relativistic Electron Losses (BARREL) reveals the simultaneous occurrence of broadband Alfvénic fluctuations and multi‐timescale modulation of enhanced atmospheric X‐ray bremsstrahlung emission. The properties of the Alfvénic fluctuations are used to build a model for pitch angle scattering in the outer radiation belt on electron gyro‐radii scale field structures. It is shown that this scattering may lead to the transport of electrons into the loss cone over an energy range from hundreds of keV to multi‐MeV on diffusive timescales on the order of hours. This process may account for modulation of atmospheric X‐ray fluxes observed from balloons and constitute a significant loss p. . .
Date: 09/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL079527 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079527
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Authors: Chaston C. C., Bonnell J. W., Wygant J R, Reeves G D, Baker D N, et al.
Title: Radiation belt “dropouts” and drift-bounce resonances in broadband electromagnetic waves
Abstract: Observations during the main phase of geomagnetic storms reveal an anti-correlation between the occurrence of broadband low frequency electromagnetic waves and outer radiation belt electron flux. We show that the drift-bounce motion of electrons in the magnetic field of these waves leads to rapid electron transport. For observed spectral energy densities it is demonstrated that the wave magnetic field can drive radial diffusion via drift-bounce resonance on timescales less than a drift orbit. This process may provide outward transport sufficient to account for electron “dropouts” during storm main phase and more generally modulate the outer radiation belt during geomagnetic storms.
Date: 02/2018 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL076362 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL076362/full
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Authors: Chaston C. C., Bonnell J. W., Reeves G D, and Skoug R M
Title: Driving ionospheric outflows and magnetospheric O + energy density with Alfvén waves
Abstract: We show how dispersive Alfvén waves observed in the inner magnetosphere during geomagnetic storms can extract O+ ions from the topside ionosphere and accelerate these ions to energies exceeding 50 keV in the equatorial plane. This occurs through wave trapping, a variant of “shock” surfing, and stochastic ion acceleration. These processes in combination with the mirror force drive field-aligned beams of outflowing ionospheric ions into the equatorial plane that evolve to provide energetic O+ distributions trapped near the equator. These waves also accelerate preexisting/injected ion populations on the same field lines. We show that the action of dispersive Alfvén waves over several minutes may drive order of magnitude increases in O+ ion pressure to make substantial contributions to. . .
Date: 05/2016 Publisher: Geophysical Research Letters Pages: 4825 - 4833 DOI: 10.1002/2016GL069008 Available at: http://doi.wiley.com/10.1002/2016GL069008
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antenna sheath impedance
Authors: Hartley D. P., Kletzing C A, Kurth W S, Hospodarsky G B, Bounds S R, et al.
Title: An improved sheath impedance model for the Van Allen probes EFW instrument: Effects of the spin axis antenna
Abstract: A technique to quantitatively determine the sheath impedance of the Van Allen Probes Electric Field and Waves (EFW) instrument is presented. This is achieved, for whistler mode waves, through a comparison between the total electric field wave power spectra calculated from magnetic field observations and cold plasma theory, and the total electric field wave power measured by the EFW spherical double probes instrument. In a previous study, a simple density-dependent sheath impedance model was developed in order to account for the differences between the observed and calculated wave electric field. The current study builds on this previous work by investigating the remaining discrepancies, identifying their cause, and developing an improved sheath impedance correction. Analysis reveals that a. . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023597 Available at: http://doi.wiley.com/10.1002/2016JA023597
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chorus spatial scales
Authors: Agapitov O., Blum L. W., Mozer F S, Bonnell J. W., and Wygant J
Title: Chorus whistler wave source scales as determined from multipoint Van Allen Probe measurements
Abstract: Whistler mode chorus waves are particularly important in outer radiation belt dynamics due to their key role in controlling the acceleration and scattering of electrons over a very wide energy range. The key parameters for both nonlinear and quasi-linear treatment of wave-particle interactions are the temporal and spatial scales of the wave source region and coherence of the wave field perturbations. Neither the source scale nor the coherence scale is well established experimentally, mostly because of a lack of multipoint VLF waveform measurements. We present an unprecedentedly long interval of coordinated VLF waveform measurements (sampled at 16384 s−1) aboard the two Van Allen Probes spacecraft—9 h (0800–1200 UT and 1700–2200 UT) during two consecutive apogees on 15 July . . .
Date: 03/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL072701 Available at: http://doi.wiley.com/10.1002/2017GL072701
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coherence scales
Authors: Blum L. W., Agapitov O., Bonnell J. W., Kletzing C., and Wygant J
Title: EMIC wave spatial and coherence scales as determined from multipoint Van Allen Probe measurements
Abstract: Electromagnetic ion cyclotron (EMIC) waves can provide a strong source of energetic electron pitch angle scattering. These waves are often quite localized, thus their spatial extent can have a large effect on their overall scattering efficiency. Using measurements from the dual Van Allen Probes, we examine four EMIC wave events observed simultaneously on the two probes at varying spacecraft separations. Correlation of both the wave amplitude and phase observed at both spacecraft is examined to estimate the active region and coherence scales of the waves. We find well-correlated wave amplitude and amplitude modulation across distances spanning hundreds to thousands of kilometers. Phase coherence persisting 30–60 s is observable during close conjunction events but is lost as spacecraft s. . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL068799 Available at: http://doi.wiley.com/10.1002/2016GL068799
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convection
Authors: Califf S., Li X, Blum L., Jaynes A., Schiller Q., et al.
Title: THEMIS measurements of quasi-static electric fields in the inner magnetosphere
Abstract: We use four years of THEMIS double-probe measurements to offer, for the first time, a complete picture of the dawn-dusk electric field covering all local times and radial distances in the inner magnetosphere based on in situ equatorial observations. This study is motivated by the results from the CRRES mission, which revealed a local maximum in the electric field developing near Earth during storm times, rather than the expected enhancement at higher L shells that is shielded near Earth as suggested by the Volland-Stern model. The CRRES observations were limited to the dusk side, while THEMIS provides complete local time coverage. We show strong agreement with the CRRES results on the dusk side, with a local maximum near L =4 for moderate levels of geomagnetic activity and evidence of stro. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020360 Available at: http://doi.wiley.com/10.1002/2014JA020360
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Diffusion
Authors: Chaston C. C., Bonnell J. W., Wygant J R, Reeves G D, Baker D N, et al.
Title: Radial transport of radiation belt electrons in kinetic field-line resonances
Abstract: A representative case study from the Van Allen Probes during a geomagnetic storm recovery phase reveals enhanced electron fluxes at intermediate pitch angles over energies from ~100 keV to 5 MeV coincident with broadband low frequency electromagnetic waves. The statistical properties of these waves are used to build a model for radial diffusion via drift-bounce resonances in kinetic Alfvén eigenmodes/kinetic field-line resonances. Estimated diffusion coefficients indicate timescales for radial transport of the order of hours in storm-time events at energies from <100 keV to MeVs over equatorial pitch angles from the edge of the loss cone to nearly perpendicular to the geomagnetic field. The correlation of kinetic resonances with electron depletions and enhancements during storm main phase. . .
Date: 07/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074587 Available at: onlinelibrary.wiley.com/doi/10.1002/2017GL074587/full
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double layers
Authors: Vasko I. Y., Agapitov O. V., Mozer F S, Bonnell J. W., Artemyev A. V., et al.
Title: Electron-acoustic solitons and double layers in the inner magnetosphere
Abstract: The Van Allen Probes observe generally two types of electrostatic solitary waves (ESW) contributing to the broadband electrostatic wave activity in the nightside inner magnetosphere. ESW with symmetric bipolar parallel electric field are electron phase space holes. The nature of ESW with asymmetric bipolar (and almost unipolar) parallel electric field has remained puzzling. To address their nature, we consider a particular event observed by Van Allen Probes to argue that during the broadband wave activity electrons with energy above 200 eV provide the dominant contribution to the total electron density, while the density of cold electrons (below a few eV) is less than a few tenths of the total electron density. We show that velocities of the asymmetric ESW are close to velocity of electron. . .
Date: 05/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074026 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL074026/full
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double probe
Authors: Califf S., Li X, Blum L., Jaynes A., Schiller Q., et al.
Title: THEMIS measurements of quasi-static electric fields in the inner magnetosphere
Abstract: We use four years of THEMIS double-probe measurements to offer, for the first time, a complete picture of the dawn-dusk electric field covering all local times and radial distances in the inner magnetosphere based on in situ equatorial observations. This study is motivated by the results from the CRRES mission, which revealed a local maximum in the electric field developing near Earth during storm times, rather than the expected enhancement at higher L shells that is shielded near Earth as suggested by the Volland-Stern model. The CRRES observations were limited to the dusk side, while THEMIS provides complete local time coverage. We show strong agreement with the CRRES results on the dusk side, with a local maximum near L =4 for moderate levels of geomagnetic activity and evidence of stro. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020360 Available at: http://doi.wiley.com/10.1002/2014JA020360
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drift‐bounce resonance
Authors: Chaston C. C., Bonnell J. W., Halford A J, Reeves G D, Baker D N, et al.
Title: Pitch Angle Scattering and Loss of Radiation Belt Electrons in Broadband Electromagnetic Waves
Abstract: A magnetic conjunction between Van Allen Probes spacecraft and the Balloon Array for Radiation‐belt Relativistic Electron Losses (BARREL) reveals the simultaneous occurrence of broadband Alfvénic fluctuations and multi‐timescale modulation of enhanced atmospheric X‐ray bremsstrahlung emission. The properties of the Alfvénic fluctuations are used to build a model for pitch angle scattering in the outer radiation belt on electron gyro‐radii scale field structures. It is shown that this scattering may lead to the transport of electrons into the loss cone over an energy range from hundreds of keV to multi‐MeV on diffusive timescales on the order of hours. This process may account for modulation of atmospheric X‐ray fluxes observed from balloons and constitute a significant loss p. . .
Date: 09/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL079527 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079527
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EFW
Authors: Hartley D. P., Kletzing C A, Kurth W S, Bounds S R, Averkamp T. F., et al.
Title: Using the cold plasma dispersion relation and whistler-mode waves to quantify the antenna sheath impedance of the Van Allen Probes EFW instrument
Abstract: Cold plasma theory and parallel wave propagation are often assumed when approximating the whistler mode magnetic field wave power from electric field observations. The current study is the first to include the wave normal angle from the Electric and Magnetic Field Instrument Suite and Integrated Science package on board the Van Allen Probes in the conversion factor, thus allowing for the accuracy of these assumptions to be quantified. Results indicate that removing the assumption of parallel propagation does not significantly affect calculated plasmaspheric hiss wave powers. Hence, the assumption of parallel propagation is valid. For chorus waves, inclusion of the wave normal angle in the conversion factor leads to significant alterations in the distribution of wave power ratios (observed/. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022501 Available at: http://doi.wiley.com/10.1002/2016JA022501
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Authors: Hartley D. P., Kletzing C A, Kurth W S, Hospodarsky G B, Bounds S R, et al.
Title: An improved sheath impedance model for the Van Allen probes EFW instrument: Effects of the spin axis antenna
Abstract: A technique to quantitatively determine the sheath impedance of the Van Allen Probes Electric Field and Waves (EFW) instrument is presented. This is achieved, for whistler mode waves, through a comparison between the total electric field wave power spectra calculated from magnetic field observations and cold plasma theory, and the total electric field wave power measured by the EFW spherical double probes instrument. In a previous study, a simple density-dependent sheath impedance model was developed in order to account for the differences between the observed and calculated wave electric field. The current study builds on this previous work by investigating the remaining discrepancies, identifying their cause, and developing an improved sheath impedance correction. Analysis reveals that a. . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023597 Available at: http://doi.wiley.com/10.1002/2016JA023597
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electric field
Authors: Califf S., Li X, Blum L., Jaynes A., Schiller Q., et al.
Title: THEMIS measurements of quasi-static electric fields in the inner magnetosphere
Abstract: We use four years of THEMIS double-probe measurements to offer, for the first time, a complete picture of the dawn-dusk electric field covering all local times and radial distances in the inner magnetosphere based on in situ equatorial observations. This study is motivated by the results from the CRRES mission, which revealed a local maximum in the electric field developing near Earth during storm times, rather than the expected enhancement at higher L shells that is shielded near Earth as suggested by the Volland-Stern model. The CRRES observations were limited to the dusk side, while THEMIS provides complete local time coverage. We show strong agreement with the CRRES results on the dusk side, with a local maximum near L =4 for moderate levels of geomagnetic activity and evidence of stro. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020360 Available at: http://doi.wiley.com/10.1002/2014JA020360
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Authors: Hartley D. P., Kletzing C A, Kurth W S, Hospodarsky G B, Bounds S R, et al.
Title: An improved sheath impedance model for the Van Allen probes EFW instrument: Effects of the spin axis antenna
Abstract: A technique to quantitatively determine the sheath impedance of the Van Allen Probes Electric Field and Waves (EFW) instrument is presented. This is achieved, for whistler mode waves, through a comparison between the total electric field wave power spectra calculated from magnetic field observations and cold plasma theory, and the total electric field wave power measured by the EFW spherical double probes instrument. In a previous study, a simple density-dependent sheath impedance model was developed in order to account for the differences between the observed and calculated wave electric field. The current study builds on this previous work by investigating the remaining discrepancies, identifying their cause, and developing an improved sheath impedance correction. Analysis reveals that a. . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023597 Available at: http://doi.wiley.com/10.1002/2016JA023597
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electron holes
Authors: Vasko I. Y., Agapitov O. V., Mozer F S, Artemyev A. V., Krasnoselskikh V. V., et al.
Title: Diffusive scattering of electrons by electron holes around injection fronts
Abstract: Van Allen Probes have detected nonlinear electrostatic spikes around injection fronts in the outer radiation belt. These spikes include electron holes (EH), double layers, and more complicated solitary waves. We show that EHs can efficiently scatter electrons due to their substantial transverse electric fields. Although the electron scattering driven by EHs is diffusive, it cannot be evaluated via the standard quasi-linear theory. We derive analytical formulas describing local electron scattering by a single EH and verify them via test particle simulations. We show that the most efficiently scattered are gyroresonant electrons (crossing EH on a time scale comparable to the local electron gyroperiod). We compute bounce-averaged diffusion coefficients and demonstrate their dependence on the . . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023337 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023337/full
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electron losses
Authors: Vasko I. Y., Agapitov O. V., Mozer F S, Artemyev A. V., Krasnoselskikh V. V., et al.
Title: Diffusive scattering of electrons by electron holes around injection fronts
Abstract: Van Allen Probes have detected nonlinear electrostatic spikes around injection fronts in the outer radiation belt. These spikes include electron holes (EH), double layers, and more complicated solitary waves. We show that EHs can efficiently scatter electrons due to their substantial transverse electric fields. Although the electron scattering driven by EHs is diffusive, it cannot be evaluated via the standard quasi-linear theory. We derive analytical formulas describing local electron scattering by a single EH and verify them via test particle simulations. We show that the most efficiently scattered are gyroresonant electrons (crossing EH on a time scale comparable to the local electron gyroperiod). We compute bounce-averaged diffusion coefficients and demonstrate their dependence on the . . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023337 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023337/full
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electron precipitation
Authors: Chaston C. C., Bonnell J. W., Wygant J R, Kletzing C A, Reeves G D, et al.
Title: Extreme ionospheric ion energization and electron heating in Alfvén waves in the storm-time inner magnetosphere
Abstract: We report measurements of energized outflowing/bouncing ionospheric ions and heated electrons in the inner magnetosphere during a geomagnetic storm. The ions arrive in the equatorial plane with pitch angles that increase with energy over a range from tens of eV to > 50 keV while the electrons are field-aligned up to ~1 keV. These particle distributions are observed during intervals of broadband low frequency electromagnetic field fluctuations consistent with a Doppler-shifted spectrum of kinetic Alfvén waves and kinetic field-line resonances. The fluctuations extend from L≈3 out to the apogee of the Van Allen Probes spacecraft at L≈6.5. They thereby span most of the L-shell range occupied by the ring current. These measurements suggest a model for ionospheric ion outflow and energizat. . .
Date: 12/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL066674 Available at: http://doi.wiley.com/10.1002/2015GL066674http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015GL066674
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Authors: Blum L. W., Halford A., Millan R., Bonnell J. W., Goldstein J, et al.
Title: Observations of coincident EMIC wave activity and duskside energetic electron precipitation on 18-19 January 2013
Abstract: Electromagnetic ion cyclotron (EMIC) waves have been suggested to be a cause of radiation belt electron loss to the atmosphere. Here simultaneous, magnetically conjugate measurements are presented of EMIC wave activity, measured at geosynchronous orbit and on the ground, and energetic electron precipitation, seen by the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) campaign, on two consecutive days in January 2013. Multiple bursts of precipitation were observed on the duskside of the magnetosphere at the end of 18 January and again late on 19 January, concurrent with particle injections, substorm activity, and enhanced magnetospheric convection. The structure, timing, and spatial extent of the waves are compared to those of the precipitation during both days to det. . .
Date: 07/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL065245 Available at: http://doi.wiley.com/10.1002/2015GL065245
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electron-acoustic waves
Authors: Vasko I. Y., Agapitov O. V., Mozer F S, Bonnell J. W., Artemyev A. V., et al.
Title: Electron-acoustic solitons and double layers in the inner magnetosphere
Abstract: The Van Allen Probes observe generally two types of electrostatic solitary waves (ESW) contributing to the broadband electrostatic wave activity in the nightside inner magnetosphere. ESW with symmetric bipolar parallel electric field are electron phase space holes. The nature of ESW with asymmetric bipolar (and almost unipolar) parallel electric field has remained puzzling. To address their nature, we consider a particular event observed by Van Allen Probes to argue that during the broadband wave activity electrons with energy above 200 eV provide the dominant contribution to the total electron density, while the density of cold electrons (below a few eV) is less than a few tenths of the total electron density. We show that velocities of the asymmetric ESW are close to velocity of electron. . .
Date: 05/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074026 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL074026/full
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EMFISIS
Authors: Hartley D. P., Kletzing C A, Kurth W S, Bounds S R, Averkamp T. F., et al.
Title: Using the cold plasma dispersion relation and whistler-mode waves to quantify the antenna sheath impedance of the Van Allen Probes EFW instrument
Abstract: Cold plasma theory and parallel wave propagation are often assumed when approximating the whistler mode magnetic field wave power from electric field observations. The current study is the first to include the wave normal angle from the Electric and Magnetic Field Instrument Suite and Integrated Science package on board the Van Allen Probes in the conversion factor, thus allowing for the accuracy of these assumptions to be quantified. Results indicate that removing the assumption of parallel propagation does not significantly affect calculated plasmaspheric hiss wave powers. Hence, the assumption of parallel propagation is valid. For chorus waves, inclusion of the wave normal angle in the conversion factor leads to significant alterations in the distribution of wave power ratios (observed/. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022501 Available at: http://doi.wiley.com/10.1002/2016JA022501
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Authors: Hartley D. P., Kletzing C A, Kurth W S, Hospodarsky G B, Bounds S R, et al.
Title: An improved sheath impedance model for the Van Allen probes EFW instrument: Effects of the spin axis antenna
Abstract: A technique to quantitatively determine the sheath impedance of the Van Allen Probes Electric Field and Waves (EFW) instrument is presented. This is achieved, for whistler mode waves, through a comparison between the total electric field wave power spectra calculated from magnetic field observations and cold plasma theory, and the total electric field wave power measured by the EFW spherical double probes instrument. In a previous study, a simple density-dependent sheath impedance model was developed in order to account for the differences between the observed and calculated wave electric field. The current study builds on this previous work by investigating the remaining discrepancies, identifying their cause, and developing an improved sheath impedance correction. Analysis reveals that a. . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023597 Available at: http://doi.wiley.com/10.1002/2016JA023597
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EMIC waves
Authors: Blum L. W., Halford A., Millan R., Bonnell J. W., Goldstein J, et al.
Title: Observations of coincident EMIC wave activity and duskside energetic electron precipitation on 18-19 January 2013
Abstract: Electromagnetic ion cyclotron (EMIC) waves have been suggested to be a cause of radiation belt electron loss to the atmosphere. Here simultaneous, magnetically conjugate measurements are presented of EMIC wave activity, measured at geosynchronous orbit and on the ground, and energetic electron precipitation, seen by the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) campaign, on two consecutive days in January 2013. Multiple bursts of precipitation were observed on the duskside of the magnetosphere at the end of 18 January and again late on 19 January, concurrent with particle injections, substorm activity, and enhanced magnetospheric convection. The structure, timing, and spatial extent of the waves are compared to those of the precipitation during both days to det. . .
Date: 07/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL065245 Available at: http://doi.wiley.com/10.1002/2015GL065245
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Authors: Blum L. W., Agapitov O., Bonnell J. W., Kletzing C., and Wygant J
Title: EMIC wave spatial and coherence scales as determined from multipoint Van Allen Probe measurements
Abstract: Electromagnetic ion cyclotron (EMIC) waves can provide a strong source of energetic electron pitch angle scattering. These waves are often quite localized, thus their spatial extent can have a large effect on their overall scattering efficiency. Using measurements from the dual Van Allen Probes, we examine four EMIC wave events observed simultaneously on the two probes at varying spacecraft separations. Correlation of both the wave amplitude and phase observed at both spacecraft is examined to estimate the active region and coherence scales of the waves. We find well-correlated wave amplitude and amplitude modulation across distances spanning hundreds to thousands of kilometers. Phase coherence persisting 30–60 s is observable during close conjunction events but is lost as spacecraft s. . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL068799 Available at: http://doi.wiley.com/10.1002/2016GL068799
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Authors: Blum L. W., Bonnell J. W., Agapitov O., Paulson K., and Kletzing C.
Title: EMIC wave scale size in the inner magnetosphere: Observations from the dual Van Allen Probes
Abstract: Estimating the spatial scales of electromagnetic ion cyclotron (EMIC) waves is critical for quantifying their overall scattering efficiency and effects on thermal plasma, ring current, and radiation belt particles. Using measurements from the dual Van Allen Probes in 2013–2014, we characterize the spatial and temporal extents of regions of EMIC wave activity and how these depend on local time and radial distance within the inner magnetosphere. Observations are categorized into three types—waves observed by only one spacecraft, waves measured by both spacecraft simultaneously, and waves observed by both spacecraft with some time lag. Analysis reveals that dayside (and H+ band) EMIC waves more frequently span larger spatial areas, while nightside (and He+ band) waves are more often loc. . .
Date: 02/2017 Publisher: Geophysical Research Letters Pages: 1227 - 1233 DOI: 10.1002/2016GL072316 Available at: http://doi.wiley.com/10.1002/2016GL072316
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energetic particles
Authors: Chaston C. C., Bonnell J. W., Halford A J, Reeves G D, Baker D N, et al.
Title: Pitch Angle Scattering and Loss of Radiation Belt Electrons in Broadband Electromagnetic Waves
Abstract: A magnetic conjunction between Van Allen Probes spacecraft and the Balloon Array for Radiation‐belt Relativistic Electron Losses (BARREL) reveals the simultaneous occurrence of broadband Alfvénic fluctuations and multi‐timescale modulation of enhanced atmospheric X‐ray bremsstrahlung emission. The properties of the Alfvénic fluctuations are used to build a model for pitch angle scattering in the outer radiation belt on electron gyro‐radii scale field structures. It is shown that this scattering may lead to the transport of electrons into the loss cone over an energy range from hundreds of keV to multi‐MeV on diffusive timescales on the order of hours. This process may account for modulation of atmospheric X‐ray fluxes observed from balloons and constitute a significant loss p. . .
Date: 09/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL079527 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079527
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field line resonances
Authors: Chaston C. C., Bonnell J. W., Wygant J R, Reeves G D, Baker D N, et al.
Title: Radial transport of radiation belt electrons in kinetic field-line resonances
Abstract: A representative case study from the Van Allen Probes during a geomagnetic storm recovery phase reveals enhanced electron fluxes at intermediate pitch angles over energies from ~100 keV to 5 MeV coincident with broadband low frequency electromagnetic waves. The statistical properties of these waves are used to build a model for radial diffusion via drift-bounce resonances in kinetic Alfvén eigenmodes/kinetic field-line resonances. Estimated diffusion coefficients indicate timescales for radial transport of the order of hours in storm-time events at energies from <100 keV to MeVs over equatorial pitch angles from the edge of the loss cone to nearly perpendicular to the geomagnetic field. The correlation of kinetic resonances with electron depletions and enhancements during storm main phase. . .
Date: 07/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074587 Available at: onlinelibrary.wiley.com/doi/10.1002/2017GL074587/full
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Geomagnetic storms
Authors: Chaston C. C., Bonnell J. W., Wygant J R, Reeves G D, Baker D N, et al.
Title: Radiation belt “dropouts” and drift-bounce resonances in broadband electromagnetic waves
Abstract: Observations during the main phase of geomagnetic storms reveal an anti-correlation between the occurrence of broadband low frequency electromagnetic waves and outer radiation belt electron flux. We show that the drift-bounce motion of electrons in the magnetic field of these waves leads to rapid electron transport. For observed spectral energy densities it is demonstrated that the wave magnetic field can drive radial diffusion via drift-bounce resonance on timescales less than a drift orbit. This process may provide outward transport sufficient to account for electron “dropouts” during storm main phase and more generally modulate the outer radiation belt during geomagnetic storms.
Date: 02/2018 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL076362 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL076362/full
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Authors: Chaston C. C., Bonnell J. W., Halford A J, Reeves G D, Baker D N, et al.
Title: Pitch Angle Scattering and Loss of Radiation Belt Electrons in Broadband Electromagnetic Waves
Abstract: A magnetic conjunction between Van Allen Probes spacecraft and the Balloon Array for Radiation‐belt Relativistic Electron Losses (BARREL) reveals the simultaneous occurrence of broadband Alfvénic fluctuations and multi‐timescale modulation of enhanced atmospheric X‐ray bremsstrahlung emission. The properties of the Alfvénic fluctuations are used to build a model for pitch angle scattering in the outer radiation belt on electron gyro‐radii scale field structures. It is shown that this scattering may lead to the transport of electrons into the loss cone over an energy range from hundreds of keV to multi‐MeV on diffusive timescales on the order of hours. This process may account for modulation of atmospheric X‐ray fluxes observed from balloons and constitute a significant loss p. . .
Date: 09/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL079527 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079527
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Authors: Chaston C. C., Bonnell J. W., Kletzing C A, Hospodarsky G B, Wygant J R, et al.
Title: Broadband low frequency electromagnetic waves in the inner magnetosphere
Abstract: A prominent yet largely unrecognized feature of the inner magnetosphere associated with particle injections, and more generally geomagnetic storms, is the occurrence of broadband electromagnetic field fluctuations over spacecraft frame frequencies (fsc) extending from effectively zero to fsc ≳ 100 Hz. Using observations from the Van Allen Probes we show that these waves most commonly occur pre-midnight but are observed over a range of local times extending into the dayside magnetosphere. We find that the variation of magnetic spectral energy density with fsc obeys inline image over several decades with a spectral break-point at fb ≈1 Hz. The values for α are log normally distributed with α = 1.9 ± 0.6 for fsc < fb andα = 2.9 ± 0.6 for fsc > fb. A is . . .
Date: 09/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021690 Available at: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015JA021690/abstract
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Authors: Chaston C. C., Bonnell J. W., Wygant J R, Kletzing C A, Reeves G D, et al.
Title: Extreme ionospheric ion energization and electron heating in Alfvén waves in the storm-time inner magnetosphere
Abstract: We report measurements of energized outflowing/bouncing ionospheric ions and heated electrons in the inner magnetosphere during a geomagnetic storm. The ions arrive in the equatorial plane with pitch angles that increase with energy over a range from tens of eV to > 50 keV while the electrons are field-aligned up to ~1 keV. These particle distributions are observed during intervals of broadband low frequency electromagnetic field fluctuations consistent with a Doppler-shifted spectrum of kinetic Alfvén waves and kinetic field-line resonances. The fluctuations extend from L≈3 out to the apogee of the Van Allen Probes spacecraft at L≈6.5. They thereby span most of the L-shell range occupied by the ring current. These measurements suggest a model for ionospheric ion outflow and energizat. . .
Date: 12/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL066674 Available at: http://doi.wiley.com/10.1002/2015GL066674http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015GL066674
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injection
Authors: Vasko I. Y., Agapitov O. V., Mozer F S, Artemyev A. V., Krasnoselskikh V. V., et al.
Title: Diffusive scattering of electrons by electron holes around injection fronts
Abstract: Van Allen Probes have detected nonlinear electrostatic spikes around injection fronts in the outer radiation belt. These spikes include electron holes (EH), double layers, and more complicated solitary waves. We show that EHs can efficiently scatter electrons due to their substantial transverse electric fields. Although the electron scattering driven by EHs is diffusive, it cannot be evaluated via the standard quasi-linear theory. We derive analytical formulas describing local electron scattering by a single EH and verify them via test particle simulations. We show that the most efficiently scattered are gyroresonant electrons (crossing EH on a time scale comparable to the local electron gyroperiod). We compute bounce-averaged diffusion coefficients and demonstrate their dependence on the . . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023337 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023337/full
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inner magnetosphere
Authors: Califf S., Li X, Blum L., Jaynes A., Schiller Q., et al.
Title: THEMIS measurements of quasi-static electric fields in the inner magnetosphere
Abstract: We use four years of THEMIS double-probe measurements to offer, for the first time, a complete picture of the dawn-dusk electric field covering all local times and radial distances in the inner magnetosphere based on in situ equatorial observations. This study is motivated by the results from the CRRES mission, which revealed a local maximum in the electric field developing near Earth during storm times, rather than the expected enhancement at higher L shells that is shielded near Earth as suggested by the Volland-Stern model. The CRRES observations were limited to the dusk side, while THEMIS provides complete local time coverage. We show strong agreement with the CRRES results on the dusk side, with a local maximum near L =4 for moderate levels of geomagnetic activity and evidence of stro. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020360 Available at: http://doi.wiley.com/10.1002/2014JA020360
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Authors: Blum L. W., Bonnell J. W., Agapitov O., Paulson K., and Kletzing C.
Title: EMIC wave scale size in the inner magnetosphere: Observations from the dual Van Allen Probes
Abstract: Estimating the spatial scales of electromagnetic ion cyclotron (EMIC) waves is critical for quantifying their overall scattering efficiency and effects on thermal plasma, ring current, and radiation belt particles. Using measurements from the dual Van Allen Probes in 2013–2014, we characterize the spatial and temporal extents of regions of EMIC wave activity and how these depend on local time and radial distance within the inner magnetosphere. Observations are categorized into three types—waves observed by only one spacecraft, waves measured by both spacecraft simultaneously, and waves observed by both spacecraft with some time lag. Analysis reveals that dayside (and H+ band) EMIC waves more frequently span larger spatial areas, while nightside (and He+ band) waves are more often loc. . .
Date: 02/2017 Publisher: Geophysical Research Letters Pages: 1227 - 1233 DOI: 10.1002/2016GL072316 Available at: http://doi.wiley.com/10.1002/2016GL072316
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Authors: Vasko I. Y., Agapitov O. V., Mozer F S, Bonnell J. W., Artemyev A. V., et al.
Title: Electron-acoustic solitons and double layers in the inner magnetosphere
Abstract: The Van Allen Probes observe generally two types of electrostatic solitary waves (ESW) contributing to the broadband electrostatic wave activity in the nightside inner magnetosphere. ESW with symmetric bipolar parallel electric field are electron phase space holes. The nature of ESW with asymmetric bipolar (and almost unipolar) parallel electric field has remained puzzling. To address their nature, we consider a particular event observed by Van Allen Probes to argue that during the broadband wave activity electrons with energy above 200 eV provide the dominant contribution to the total electron density, while the density of cold electrons (below a few eV) is less than a few tenths of the total electron density. We show that velocities of the asymmetric ESW are close to velocity of electron. . .
Date: 05/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074026 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL074026/full
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ion acceleration
Authors: Chaston C. C., Bonnell J. W., Reeves G D, and Skoug R M
Title: Driving ionospheric outflows and magnetospheric O + energy density with Alfvén waves
Abstract: We show how dispersive Alfvén waves observed in the inner magnetosphere during geomagnetic storms can extract O+ ions from the topside ionosphere and accelerate these ions to energies exceeding 50 keV in the equatorial plane. This occurs through wave trapping, a variant of “shock” surfing, and stochastic ion acceleration. These processes in combination with the mirror force drive field-aligned beams of outflowing ionospheric ions into the equatorial plane that evolve to provide energetic O+ distributions trapped near the equator. These waves also accelerate preexisting/injected ion populations on the same field lines. We show that the action of dispersive Alfvén waves over several minutes may drive order of magnitude increases in O+ ion pressure to make substantial contributions to. . .
Date: 05/2016 Publisher: Geophysical Research Letters Pages: 4825 - 4833 DOI: 10.1002/2016GL069008 Available at: http://doi.wiley.com/10.1002/2016GL069008
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Authors: Chaston C. C., Bonnell J. W., Wygant J R, Kletzing C A, Reeves G D, et al.
Title: Extreme ionospheric ion energization and electron heating in Alfvén waves in the storm-time inner magnetosphere
Abstract: We report measurements of energized outflowing/bouncing ionospheric ions and heated electrons in the inner magnetosphere during a geomagnetic storm. The ions arrive in the equatorial plane with pitch angles that increase with energy over a range from tens of eV to > 50 keV while the electrons are field-aligned up to ~1 keV. These particle distributions are observed during intervals of broadband low frequency electromagnetic field fluctuations consistent with a Doppler-shifted spectrum of kinetic Alfvén waves and kinetic field-line resonances. The fluctuations extend from L≈3 out to the apogee of the Van Allen Probes spacecraft at L≈6.5. They thereby span most of the L-shell range occupied by the ring current. These measurements suggest a model for ionospheric ion outflow and energizat. . .
Date: 12/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL066674 Available at: http://doi.wiley.com/10.1002/2015GL066674http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015GL066674
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ion outflow
Authors: Chaston C. C., Bonnell J. W., Wygant J R, Kletzing C A, Reeves G D, et al.
Title: Extreme ionospheric ion energization and electron heating in Alfvén waves in the storm-time inner magnetosphere
Abstract: We report measurements of energized outflowing/bouncing ionospheric ions and heated electrons in the inner magnetosphere during a geomagnetic storm. The ions arrive in the equatorial plane with pitch angles that increase with energy over a range from tens of eV to > 50 keV while the electrons are field-aligned up to ~1 keV. These particle distributions are observed during intervals of broadband low frequency electromagnetic field fluctuations consistent with a Doppler-shifted spectrum of kinetic Alfvén waves and kinetic field-line resonances. The fluctuations extend from L≈3 out to the apogee of the Van Allen Probes spacecraft at L≈6.5. They thereby span most of the L-shell range occupied by the ring current. These measurements suggest a model for ionospheric ion outflow and energizat. . .
Date: 12/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL066674 Available at: http://doi.wiley.com/10.1002/2015GL066674http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015GL066674
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ion upflo
Authors: Chaston C. C., Bonnell J. W., Wygant J R, Kletzing C A, Reeves G D, et al.
Title: Extreme ionospheric ion energization and electron heating in Alfvén waves in the storm-time inner magnetosphere
Abstract: We report measurements of energized outflowing/bouncing ionospheric ions and heated electrons in the inner magnetosphere during a geomagnetic storm. The ions arrive in the equatorial plane with pitch angles that increase with energy over a range from tens of eV to > 50 keV while the electrons are field-aligned up to ~1 keV. These particle distributions are observed during intervals of broadband low frequency electromagnetic field fluctuations consistent with a Doppler-shifted spectrum of kinetic Alfvén waves and kinetic field-line resonances. The fluctuations extend from L≈3 out to the apogee of the Van Allen Probes spacecraft at L≈6.5. They thereby span most of the L-shell range occupied by the ring current. These measurements suggest a model for ionospheric ion outflow and energizat. . .
Date: 12/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL066674 Available at: http://doi.wiley.com/10.1002/2015GL066674http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015GL066674
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Ionosphere
Authors: Chaston C. C., Bonnell J. W., Reeves G D, and Skoug R M
Title: Driving ionospheric outflows and magnetospheric O + energy density with Alfvén waves
Abstract: We show how dispersive Alfvén waves observed in the inner magnetosphere during geomagnetic storms can extract O+ ions from the topside ionosphere and accelerate these ions to energies exceeding 50 keV in the equatorial plane. This occurs through wave trapping, a variant of “shock” surfing, and stochastic ion acceleration. These processes in combination with the mirror force drive field-aligned beams of outflowing ionospheric ions into the equatorial plane that evolve to provide energetic O+ distributions trapped near the equator. These waves also accelerate preexisting/injected ion populations on the same field lines. We show that the action of dispersive Alfvén waves over several minutes may drive order of magnitude increases in O+ ion pressure to make substantial contributions to. . .
Date: 05/2016 Publisher: Geophysical Research Letters Pages: 4825 - 4833 DOI: 10.1002/2016GL069008 Available at: http://doi.wiley.com/10.1002/2016GL069008
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ionospheric outflow
Authors: Chaston C. C., Bonnell J. W., Reeves G D, and Skoug R M
Title: Driving ionospheric outflows and magnetospheric O + energy density with Alfvén waves
Abstract: We show how dispersive Alfvén waves observed in the inner magnetosphere during geomagnetic storms can extract O+ ions from the topside ionosphere and accelerate these ions to energies exceeding 50 keV in the equatorial plane. This occurs through wave trapping, a variant of “shock” surfing, and stochastic ion acceleration. These processes in combination with the mirror force drive field-aligned beams of outflowing ionospheric ions into the equatorial plane that evolve to provide energetic O+ distributions trapped near the equator. These waves also accelerate preexisting/injected ion populations on the same field lines. We show that the action of dispersive Alfvén waves over several minutes may drive order of magnitude increases in O+ ion pressure to make substantial contributions to. . .
Date: 05/2016 Publisher: Geophysical Research Letters Pages: 4825 - 4833 DOI: 10.1002/2016GL069008 Available at: http://doi.wiley.com/10.1002/2016GL069008
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Kelvin-Helmholtz
Authors: Walsh B. M., Thomas E. G., Hwang K.-J., Baker J. B. H., Ruohoniemi J. M., et al.
Title: Dense plasma and Kelvin-Helmholtz waves at Earth's dayside magnetopause
Abstract: Spacecraft observations of boundary waves at the dayside terrestrial magnetopause and their ground-based signatures are presented. Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measured boundary waves at the magnetopause while ground-based HF radar measured corresponding signatures in the ionosphere indicating a large-scale response and tailward propagating waves. The properties of the oscillations are consistent with linear phase Kelvin-Helmholtz waves along the magnetopause boundary. During this time period multiple THEMIS spacecraft also measured a plasmaspheric plume contacting the local magnetopause and mass loading the boundary. Previous work has demonstrated that increasing the density at the magnetopause can lower the efficiency of reconnec. . .
Date: 07/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021014 Available at: http://doi.wiley.com/10.1002/2015JA021014
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magnetopause
Authors: Walsh B. M., Thomas E. G., Hwang K.-J., Baker J. B. H., Ruohoniemi J. M., et al.
Title: Dense plasma and Kelvin-Helmholtz waves at Earth's dayside magnetopause
Abstract: Spacecraft observations of boundary waves at the dayside terrestrial magnetopause and their ground-based signatures are presented. Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measured boundary waves at the magnetopause while ground-based HF radar measured corresponding signatures in the ionosphere indicating a large-scale response and tailward propagating waves. The properties of the oscillations are consistent with linear phase Kelvin-Helmholtz waves along the magnetopause boundary. During this time period multiple THEMIS spacecraft also measured a plasmaspheric plume contacting the local magnetopause and mass loading the boundary. Previous work has demonstrated that increasing the density at the magnetopause can lower the efficiency of reconnec. . .
Date: 07/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021014 Available at: http://doi.wiley.com/10.1002/2015JA021014
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multipoint
Authors: Blum L. W., Bonnell J. W., Agapitov O., Paulson K., and Kletzing C.
Title: EMIC wave scale size in the inner magnetosphere: Observations from the dual Van Allen Probes
Abstract: Estimating the spatial scales of electromagnetic ion cyclotron (EMIC) waves is critical for quantifying their overall scattering efficiency and effects on thermal plasma, ring current, and radiation belt particles. Using measurements from the dual Van Allen Probes in 2013–2014, we characterize the spatial and temporal extents of regions of EMIC wave activity and how these depend on local time and radial distance within the inner magnetosphere. Observations are categorized into three types—waves observed by only one spacecraft, waves measured by both spacecraft simultaneously, and waves observed by both spacecraft with some time lag. Analysis reveals that dayside (and H+ band) EMIC waves more frequently span larger spatial areas, while nightside (and He+ band) waves are more often loc. . .
Date: 02/2017 Publisher: Geophysical Research Letters Pages: 1227 - 1233 DOI: 10.1002/2016GL072316 Available at: http://doi.wiley.com/10.1002/2016GL072316
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multipoint measurements
Authors: Blum L. W., Agapitov O., Bonnell J. W., Kletzing C., and Wygant J
Title: EMIC wave spatial and coherence scales as determined from multipoint Van Allen Probe measurements
Abstract: Electromagnetic ion cyclotron (EMIC) waves can provide a strong source of energetic electron pitch angle scattering. These waves are often quite localized, thus their spatial extent can have a large effect on their overall scattering efficiency. Using measurements from the dual Van Allen Probes, we examine four EMIC wave events observed simultaneously on the two probes at varying spacecraft separations. Correlation of both the wave amplitude and phase observed at both spacecraft is examined to estimate the active region and coherence scales of the waves. We find well-correlated wave amplitude and amplitude modulation across distances spanning hundreds to thousands of kilometers. Phase coherence persisting 30–60 s is observable during close conjunction events but is lost as spacecraft s. . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL068799 Available at: http://doi.wiley.com/10.1002/2016GL068799
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pitch‐angle scattering
Authors: Chaston C. C., Bonnell J. W., Halford A J, Reeves G D, Baker D N, et al.
Title: Pitch Angle Scattering and Loss of Radiation Belt Electrons in Broadband Electromagnetic Waves
Abstract: A magnetic conjunction between Van Allen Probes spacecraft and the Balloon Array for Radiation‐belt Relativistic Electron Losses (BARREL) reveals the simultaneous occurrence of broadband Alfvénic fluctuations and multi‐timescale modulation of enhanced atmospheric X‐ray bremsstrahlung emission. The properties of the Alfvénic fluctuations are used to build a model for pitch angle scattering in the outer radiation belt on electron gyro‐radii scale field structures. It is shown that this scattering may lead to the transport of electrons into the loss cone over an energy range from hundreds of keV to multi‐MeV on diffusive timescales on the order of hours. This process may account for modulation of atmospheric X‐ray fluxes observed from balloons and constitute a significant loss p. . .
Date: 09/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL079527 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079527
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Plasmaspheric Hiss
Authors: Hartley D. P., Kletzing C A, Kurth W S, Bounds S R, Averkamp T. F., et al.
Title: Using the cold plasma dispersion relation and whistler-mode waves to quantify the antenna sheath impedance of the Van Allen Probes EFW instrument
Abstract: Cold plasma theory and parallel wave propagation are often assumed when approximating the whistler mode magnetic field wave power from electric field observations. The current study is the first to include the wave normal angle from the Electric and Magnetic Field Instrument Suite and Integrated Science package on board the Van Allen Probes in the conversion factor, thus allowing for the accuracy of these assumptions to be quantified. Results indicate that removing the assumption of parallel propagation does not significantly affect calculated plasmaspheric hiss wave powers. Hence, the assumption of parallel propagation is valid. For chorus waves, inclusion of the wave normal angle in the conversion factor leads to significant alterations in the distribution of wave power ratios (observed/. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022501 Available at: http://doi.wiley.com/10.1002/2016JA022501
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