Biblio

Found 643 results
Filters: Keyword is Van Allen Probes  [Clear All Filters]
Journal Article
Authors: Lejosne Solène, and Mozer F S
Title: Van Allen Probe measurements of the electric drift E × B/B2 at Arecibo's L = 1.4 field line coordinate
Abstract: We have used electric and magnetic measurements by Van Allen Probe B from 2013 to 2014 to examine the equatorial electric drift E × B/B2 at one field line coordinate set to Arecibo's incoherent scatter radar location (L = 1.43). We report on departures from the traditional picture of corotational motion with the Earth in two ways: (1) the rotational angular speed is found to be 10% smaller than the rotational angular speed of the Earth, in agreement with previous works on plasmaspheric notches, and (2) the equatorial electric drift displays a dependence in magnetic local time, with a pattern consistent with the mapping of the Arecibo ionosphere dynamo electric fields along equipotential magnetic field lines. The electric fields due to the ionosphere dynamo are therefore expected t. . .
Date: 07/2016 Publisher: Geophysical Research Letters Pages: 6768 - 6774 DOI: 10.1002/2016GL069875 Available at: http://doi.wiley.com/10.1002/2016GL069875
More Details
Authors: Korotova G. I., Sibeck D G, Tahakashi K., Dai L., Spence H E, et al.
Title: Van Allen Probe observations of drift-bounce resonances with Pc 4 pulsations and wave–particle interactions in the pre-midnight inner magnetosphere
Abstract: We present Van Allen Probe B observations of azimuthally limited, antisymmetric, poloidal Pc 4 electric and magnetic field pulsations in the pre-midnight sector of the magnetosphere from 05:40 to 06:00 UT on 1 May 2013. Oscillation periods were similar for the magnetic and electric fields and proton fluxes. The flux of energetic protons exhibited an energy-dependent response to the pulsations. Energetic proton variations were anticorrelated at medium and low energies. Although we attribute the pulsations to a drift-bounce resonance, we demonstrate that the energy-dependent response of the ion fluxes results from pulsation-associated velocities sweeping energy-dependent radial ion flux gradients back and forth past the spacecraft.
Date: 01/2015 Publisher: Annales Geophysicae Pages: 955 - 964 DOI: 10.5194/angeo-33-955-2015 Available at: http://www.ann-geophys.net/33/955/2015/angeo-33-955-2015.pdf
More Details
Authors: Boardsen S. A., Hospodarsky G B, Kletzing C A, Pfaff R. F., Kurth W S, et al.
Title: Van Allen Probe Observations of Periodic Rising Frequencies of the Fast Magnetosonic Mode
Abstract: Near simultaneous periodic dispersive features of fast magnetosonic mode emissions are observed by both Van Allen Probes spacecraft while separated in magnetic local time by ~5 hours: Probe A at 15 and Probe B at 9–11 hours. Both spacecraft see similar frequency features, characterized by a periodic repetition at ~180 s. Each repetition is characterized by a rising frequency. Since no modulation is observed in the proton shell distribution, the plasma density, or in the background magnetic field at either spacecraft we conclude that these waves are not generated near the spacecraft but external to both spacecraft locations. Probe A while outside the plasmapause sees the start of each repetition ~40 s before probe B while deep inside the plasmasphere. We can qualitatively reproduce . . .
Date: 12/2014 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062020 Available at: http://doi.wiley.com/10.1002/2014GL062020
More Details
Authors: Thaller S. A., Wygant J R, Dai L., Breneman A.W., Kersten K., et al.
Title: Van Allen Probes investigation of the large scale duskward electric field and its role in ring current formation and plasmasphere erosion in the June 1, 2013 storm
Abstract: Using the Van Allen Probes we investigate the enhancement in the large scale duskward convection electric field during the geomagnetic storm (Dst ~ −120 nT) on June 1, 2013 and its role in ring current ion transport and energization, and plasmasphere erosion. During this storm, enhancements of ~1-2 mV/m in the duskward electric field in the co-rotating frame are observed down to L shells as low as ~2.3. A simple model consisting of a dipole magnetic field and constant, azimuthally westward, electric field is used to calculate the earthward and westward drift of 90° pitch angle ions. This model is applied to determine how far earthward ions can drift while remaining on Earth's night side, given the strength and duration of the convection electric field. The calculation based on this simp. . .
Date: 05/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020875 Available at: http://doi.wiley.com/10.1002/2014JA020875
More Details
Authors: Engebretson M. J., Posch J. L., Wygant J R, Kletzing C A, Lessard M. R., et al.
Title: Van Allen probes, NOAA, GOES, and ground observations of an intense EMIC wave event extending over 12 hours in MLT
Abstract: Although most studies of the effects of EMIC waves on Earth's outer radiation belt have focused on events in the afternoon sector in the outer plasmasphere or plume region, strong magnetospheric compressions provide an additional stimulus for EMIC wave generation across a large range of local times and L shells. We present here observations of the effects of a wave event on February 23, 2014 that extended over 8 hours in UT and over 12 hours in local time, stimulated by a gradual 4-hour rise and subsequent sharp increases in solar wind pressure. Large-amplitude linearly polarized hydrogen band EMIC waves (up to 25 nT p-p) appeared for over 4 hours at both Van Allen Probes, from late morning through local noon, when these spacecraft were outside the plasmapause, with densities ~5-20 cm-3. W. . .
Date: 06/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021227 Available at: http://doi.wiley.com/10.1002/2015JA021227
More Details
Authors: He Yihua, Xiao Fuliang, Zhou Qinghua, Yang Chang, Liu Si, et al.
Title: Van Allen Probes observation and modeling of chorus excitation and propagation during weak geomagnetic activities
Abstract: We report correlated data on nightside chorus waves and energetic electrons during two small storm periods: 1 November 2012 (Dst≈-45) and 14 January 2013 (Dst≈-18). The Van Allen Probes simultaneously observed strong chorus waves at locations L = 5.8 − 6.3, with a lower frequency band 0.1 − 0.5fce and a peak spectral density ∼[10−4 nT2/Hz. In the same period, the fluxes and anisotropy of energetic (∼ 10-300 keV) electrons were greatly enhanced in the interval of large negative interplanetary magnetic field Bz. Using a bi-Maxwellian distribution to model the observed electron distribution, we perform ray tracing simulations to show that nightside chorus waves are indeed produced by the observed electron distribution with a peak growth for a field-aligned propagation around bet. . .
Date: 07/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021376 Available at: http://doi.wiley.com/10.1002/2015JA021376
More Details
Authors: Chen X.-R., Zong Q.-G., Zhou X.-Z., Blake Bernard, Wygant John R., et al.
Title: Van Allen Probes observation of a 360° phase shift in the flux modulation of injected electrons by ULF waves
Abstract: We present Van Allen Probe observation of drift-resonance interaction between energetic electrons and ultra-low frequency (ULF) waves on October 29, 2013. Oscillations in electron flux were observed at the period of ∼450s, which is also the dominant period of the observed ULF magnetic pulsations. The phase shift of the electron fluxes (∼50 to 150 keV) across the estimated resonant energy (∼104 keV) is ∼360°. This phase relationship is different from the characteristic 180° phase shift as expected from the drift-resonance theory. We speculate that the additional 180° phase difference arises from the inversion of electron phase space density (PSD) gradient, which in turn is caused by the drift motion of the substorm injected electrons. This PSD gradient adjusts the characteristic . . .
Date: 12/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL071252 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL071252/full
More Details
Authors: Chen X.-R., Zong Q.-G., Zhou X.-Z., Blake Bernard, Wygant J. R., et al.
Title: Van Allen Probes observation of a 360° phase shift in the flux modulation of injected electrons by ULF waves
Abstract: We present Van Allen Probe observation of drift-resonance interaction between energetic electrons and ultralow frequency (ULF) waves on 29 October 2013. Oscillations in electron flux were observed at the period of ∼450 s, which is also the dominant period of the observed ULF magnetic pulsations. The phase shift of the electron fluxes (∼50 to 150 keV) across the estimated resonant energy (∼104 keV) is ∼360°. This phase relationship is different from the characteristic 180° phase shift as expected from the drift-resonance theory. We speculate that the additional 180° phase difference arises from the inversion of electron phase space density (PSD) gradient, which in turn is caused by the drift motion of the substorm injected electrons. This PSD gradient adjusts the characteristic p. . .
Date: 02/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL071252 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL071252/full
More Details
Authors: Takahashi Kazue, Claudepierre S G, Rankin Robert, Mann Ian, and Smith C W
Title: Van Allen Probes Observation of a Fundamental Poloidal Standing Alfvén Wave Event Related to Giant Pulsations
Abstract: The Van Allen Probes‐A spacecraft observed an ∼9 mHz ultra‐low‐frequency wave on 6 October 2012, at L∼ 5.7, in the dawn sector, and very near the magnetic equator. The wave had a strong electric field that was initially stronger in the azimuthal component and later in the radial component, exhibited properties of a fundamental standing Alfvén wave, and was associated with giant pulsations observed on the ground near the magnetic field footprint of the spacecraft. The wave was accompanied by oscillations of the flux of energetic protons (jH+). The amplitude of urn:x-wiley:jgra:media:jgra54254:jgra54254-math-0001 oscillations was large at equatorial pitch angles away from 90°, and the energy dependence of the phase and amplitude of the oscillations exhibited features consistent w. . .
Date: 05/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2017JA025139 Available at: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2017JA025139
More Details
Authors: Claudepierre S G, Mann I R, Takahashi K, Fennell J F, Hudson M K, et al.
Title: Van Allen Probes observation of localized drift-resonance between poloidal mode ultra-low frequency waves and 60 keV electrons
Abstract: [1] We present NASA Van Allen Probes observations of wave-particle interactions between magnetospheric ultra-low frequency (ULF) waves and energetic electrons (20–500 keV) on 31 October 2012. The ULF waves are identified as the fundamental poloidal mode oscillation and are excited following an interplanetary shock impact on the magnetosphere. Large amplitude modulations in energetic electron flux are observed at the same period (≈ 3 min) as the ULF waves and are consistent with a drift-resonant interaction. The azimuthal mode number of the interacting wave is estimated from the electron measurements to be ~40, based on an assumed symmetric drift resonance. The drift-resonant interaction is observed to be localized and occur over 5–6 wave cycles, demonstrating peak electron flux modul. . .
Date: 09/2013 Publisher: Geophysical Research Letters Pages: 4491–4497 DOI: 10.1002/grl.50901 Available at: http://onlinelibrary.wiley.com/doi/10.1002/grl.50901/full
More Details
Authors: Hartley D. P., Kletzing C A, Chen L, Horne R B, and ík O.
Title: Van Allen Probes observations of chorus wave vector orientations: Implications for the chorus-to-hiss mechanism
Abstract: Using observations from the Van Allen Probes EMFISIS instrument, coupled with ray tracing simulations, we determine the fraction of chorus wave power with the conditions required to access the plasmasphere and evolve into plasmaspheric hiss. It is found that only an extremely small fraction of chorus occurs with the required wave vector orientation, carrying only a small fraction of the total chorus wave power. The exception is on the edge of plasmaspheric plumes, where strong azimuthal density gradients are present. In these cases, up to 94% of chorus wave power exists with the conditions required to access the plasmasphere. As such, we conclude that strong azimuthal density gradients are actually a requirement if a significant fraction of chorus wave power is to enter the plasmasphere an. . .
Date: 02/2019 Publisher: Geophysical Research Letters DOI: 10.1029/2019GL082111 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL082111
More Details
Authors: Colpitts C. A., Cattell C. A., Engebretson M., Broughton M., Tian S., et al.
Title: Van Allen Probes observations of cross-scale coupling between electromagnetic ion cyclotron waves and higher-frequency wave modes
Abstract: We present observations of higher-frequency (~50–2500 Hz, ~0.1–0.7 fce) wave modes modulated at the frequency of colocated lower frequency (0.5–2 Hz, on the order of fci) waves. These observations come from the Van Allen Probes Electric Field and Waves instrument's burst mode data and represent the first observations of coupling between waves in these frequency ranges. The higher-frequency wave modes, typically whistler mode hiss and chorus or magnetosonic waves, last for a few to a few tens of seconds but are in some cases observed repeatedly over several hours. The higher-frequency waves are observed to be unmodulated before and after the presence of the electromagnetic ion cyclotron (EMIC) waves, but when the EMIC waves are present, the amplitude of the higher-frequency waves . . .
Date: 11/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL071566 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL071566/full
More Details
Authors: Fennell J. F., Roeder J. L., Kurth W S, Henderson M G, Larsen B A, et al.
Title: Van Allen Probes observations of direct wave-particle interactions
Abstract: Quasiperiodic increases, or “bursts,” of 17–26 keV electron fluxes in conjunction with chorus wave bursts were observed following a plasma injection on 13 January 2013. The pitch angle distributions changed during the burst events, evolving from sinN(α) to distributions that formed maxima at α = 75–80°, while fluxes at 90° and <60° remained nearly unchanged. The observations occurred outside of the plasmasphere in the postmidnight region and were observed by both Van Allen Probes. Density, cyclotron frequency, and pitch angle of the peak flux were used to estimate resonant electron energy. The result of ~15–35 keV is consistent with the energies of the electrons showing the flux enhancements and corresponds to electrons in and above the steep flux gradient that signa. . .
Date: 03/2014 Publisher: Geophysical Research Letters Pages: 1869 - 1875 DOI: 10.1002/2013GL059165 Available at: http://doi.wiley.com/10.1002/2013GL059165
More Details
Authors: Oimatsu S., é M., Takahashi K., Yamamoto K., Keika K, et al.
Title: Van Allen Probes observations of drift-bounce resonance and energy transfer between energetic ring current protons and poloidal Pc4 wave
Abstract: A poloidal Pc4 wave and proton flux oscillations are observed in the inner magnetosphere on the dayside near the magnetic equator by the Van Allen Probes spacecraft on 2 March 2014. The flux oscillations are observed in the energy range of 67.0 keV to 268.8 keV with the same frequency of the poloidal Pc4 wave. We find pitch angle and energy dispersion in the phase difference between the poloidal magnetic field and the proton flux oscillations, which are features of drift‐bounce resonance. We estimate the resonance energy to be ~120 keV for pitch angle (α) of 30° or 150°, and 170–180 keV for α = 50° or 130°. To examine the direction of energy flow between protons and the wave, we calculate the sign of the gradient of proton phase space density (df/dW) on both the inbound and outbo. . .
Date: 04/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2017JA025087 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2017JA025087
More Details
Authors: Cho J.-H., Lee D.-Y., Noh S.-J., Shin D.-K., Hwang J., et al.
Title: Van Allen Probes Observations of Electromagnetic Ion Cyclotron Waves Triggered by Enhanced Solar Wind Dynamic Pressure
Abstract: Magnetospheric compression due to impact of enhanced solar wind dynamic pressure Pdyn has long been considered as one of the generation mechanisms of electromagnetic ion cyclotron (EMIC) waves. With the Van Allen Probe-A observations, we identify three EMIC wave events that are triggered by Pdyn enhancements under prolonged northward IMF quiet time preconditions. They are in contrast to one another in a few aspects. Event 1 occurs in the middle of continuously increasing Pdyn while Van Allen Probe-A is located outside the plasmapause at post-midnight and near the equator (magnetic latitude (MLAT) ~ -3o). Event 2 occurs by a sharp Pdyn pulse impact while Van Allen Probe-A is located inside the plasmapause in the dawn sector and rather away from the equator (MLAT ~ 12o). Event 3 is c. . .
Date: 09/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022841 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA022841/full
More Details
Authors: é M., Keika K, Kletzing C A, Spence H E, Smith C W, et al.
Title: Van Allen Probes observations of magnetic field dipolarization and its associated O + flux variations in the inner magnetosphere at L  < 6.6
Abstract: We investigate magnetic field dipolarization in the inner magnetosphere and its associated ion flux variations, using the magnetic field and energetic ion flux data acquired by the Van Allen Probes. From a study of 74 events that appeared at L = 4.5–6.6 between 1 October 2012 and 31 October 2013, we reveal the following characteristics of the dipolarization in the inner magnetosphere: (1) its timescale is approximately 5 min, (2) it is accompanied by strong magnetic fluctuations that have a dominant frequency close to the O+ gyrofrequency, (3) ion fluxes at 20–50 keV are simultaneously enhanced with larger magnitudes for O+ than for H+, (4) after a few minutes of the dipolarization, the flux enhancement at 0.1–5 keV appears with a clear energy-dispersion signature only for . . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022549 Available at: http://doi.wiley.com/10.1002/2016JA022549
More Details
Authors: Usanova M. E., Malaspina D. M., Jaynes A. N., Bruder R. J., Mann I. R., et al.
Title: Van Allen Probes observations of oxygen cyclotron harmonic waves in the inner magnetosphere
Abstract: Waves with frequencies in the vicinity of the oxygen cyclotron frequency and its harmonics have been regularly observed on the Van Allen Probes satellites during geomagnetic storms. We focus on properties of these waves and present events from the main phase of two storms on 1 November 2012 and 17 March 2013 and associated dropouts of a few MeV electron fluxes. They are electromagnetic, in the frequency range ~0.5 to several Hz, and amplitude ~0.1 to a few nT in magnetic and ~0.1 to a few mV/m in electric field, with both the wave velocity and the Poynting vector directed almost parallel to the background magnetic field. These properties are very similar to those of electromagnetic ion cyclotron waves, which are believed to contribute to loss of ring current ions and radiation belt electro. . .
Date: 09/2016 Publisher: Geophysical Research Letters Pages: 8827 - 8834 DOI: 10.1002/grl.v43.1710.1002/2016GL070233 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL070233/abstract
More Details
Authors: Foster J. C., Erickson P. J., Omura Y., Baker D N, Kletzing C A, et al.
Title: Van Allen Probes Observations of Prompt MeV Radiation Belt Electron Acceleration in Non-Linear Interactions with VLF Chorus
Abstract: Prompt recovery of MeV electron populations in the post-storm core of the outer terrestrial radiation belt involves local acceleration of a seed population of energetic electrons in interactions with VLF chorus waves. Electron interactions during the generation of VLF rising tones are strongly non-linear, such that a fraction of the relativistic electrons at resonant energies are trapped by waves, leading to significant non-adiabatic energy exchange. Through detailed examination of VLF chorus and electron fluxes observed by Van Allen Probes, we investigate the efficiency of non-linear processes for acceleration of electrons to MeV energies. We find through subpacket analysis of chorus waveforms that electrons with initial energy 100s keV - 3 MeV can be accelerated by 50 keV - 200 keV in re. . .
Date: 12/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023429 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023429/full
More Details
Authors: Foster J. C., Erickson P. J., Omura Y., Baker D. N., Kletzing C. A., et al.
Title: Van Allen Probes observations of prompt MeV radiation belt electron acceleration in nonlinear interactions with VLF chorus
Abstract: Prompt recovery of MeV (millions of electron Volts) electron populations in the poststorm core of the outer terrestrial radiation belt involves local acceleration of a seed population of energetic electrons in interactions with VLF chorus waves. Electron interactions during the generation of VLF rising tones are strongly nonlinear, such that a fraction of the relativistic electrons at resonant energies are trapped by waves, leading to significant nonadiabatic energy exchange. Through detailed examination of VLF chorus and electron fluxes observed by Van Allen Probes, we investigate the efficiency of nonlinear processes for acceleration of electrons to MeV energies. We find through subpacket analysis of chorus waveforms that electrons with initial energy of hundreds of keV to 3 MeV can be a. . .
Date: 01/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023429 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023429
More Details
Authors: Takahashi Kazue, Oimatsu Satoshi, é Masahito, Min Kyungguk, Claudepierre Seth G., et al.
Title: Van Allen Probes Observations of Second Harmonic Poloidal Standing Alfvén Waves
Abstract: Long-lasting second-harmonic poloidal standing Alfvén waves (P2 waves) were observed by the twin Van Allen Probes (Radiation Belt Storm Probes, or RBSP) spacecraft in the noon sector of the plasmasphere, when the spacecraft were close to the magnetic equator and had a small azimuthal separation. Oscillations of proton fluxes at the wave frequency (∼10 mHz) were also observed in the energy (W) range 50–300 keV. Using the unique RBSP orbital configuration, we determined the phase delay of magnetic field perturbations between the spacecraft with a 2nπ ambiguity. We then used finite gyroradius effects seen in the proton flux oscillations to remove the ambiguity and found that the waves were propagating westward with an azimuthal wave number (m) of ∼−200. The phase of the proton flux . . .
Date: 01/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024869 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024869/full
More Details
Authors: Woodroffe J. R., Jordanova V K, Funsten H O, Streltsov A. V., Bengtson M. T., et al.
Title: Van Allen Probes observations of structured whistler mode activity and coincident electron Landau acceleration inside a remnant plasmaspheric plume
Abstract: We present observations from the Van Allen Probes spacecraft that identify a region of intense whistler mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became nonlinearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement.
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA022219 Available at: http://doi.wiley.com/10.1002/2015JA022219
More Details
Authors: Woodroffe J. R., Jordanova V. K., Funsten H. O., Streltsov A. V., Bengtson M. T., et al.
Title: Van Allen Probes Observations of Structured Whistler-mode Activity and Coincident Electron Landau Acceleration Inside a Remnant Plasmaspheric Plume
Abstract: We present observations from the Van Allen Probes spacecraft that identify an region of intense whistler-mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became non-linearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement.
Date: 02/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA022219 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2015JA022219/full
More Details
Authors: Cattell C. A., Breneman A. W., Thaller S. A., Wygant J R, Kletzing C A, et al.
Title: Van Allen Probes observations of unusually low frequency whistler mode waves observed in association with moderate magnetic storms: Statistical study
Abstract: We show the first evidence for locally excited chorus at frequencies below 0.1 fce (electron cyclotron frequency) in the outer radiation belt. A statistical study of chorus during geomagnetic storms observed by the Van Allen Probes found that frequencies are often dramatically lower than expected. The frequency at peak power suddenly stops tracking the equatorial 0.5 fce and f/fce decreases rapidly, often to frequencies well below 0.1 fce (in situ and mapped to equator). These very low frequency waves are observed both when the satellites are close to the equatorial plane and at higher magnetic latitudes. Poynting flux is consistent with generation at the equator. Wave amplitudes can be up to 20 to 40 mV/m and 2 to 4 nT. We conclude that conditions during moderate to large storms. . .
Date: 09/2015 Publisher: Geophysical Research Letters Pages: 7273 - 7281 DOI: 10.1002/2015GL065565 Available at: http://doi.wiley.com/10.1002/2015GL065565http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015GL065565
More Details
Authors: Gao Zhonglei, Su Zhenpeng, Chen Lunjin, Zheng Huinan, Wang Yuming, et al.
Title: Van Allen Probes observations of whistler-mode chorus with long-lived oscillating tones
Abstract: Whistler-mode chorus plays an important role in the radiation belt electron dynamics. In the frequency-time spectrogram, chorus often appears as a hiss-like band and/or a series of short-lived (up to ∼1 s) discrete elements. Here we present some rarely reported chorus emissions with long-lived (up to 25 s) oscillating tones observed by the Van Allen Probes in the dayside (MLT ∼9–14) midlatitude (|MLAT|>15°) region. An oscillating tone can behave either regularly or irregularly and can even transform into a nearly constant tone (with a relatively narrow frequency sweep range). We suggest that these highly coherent oscillating tones were generated naturally rather than being related to some artificial VLF transmitters. Possible scenarios for the generation of the oscillating tone chor. . .
Date: 06/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL073420 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL073420/full
More Details
Authors: Fennell J. F., Claudepierre S G, Blake J B, O'Brien T P, Clemmons J. H., et al.
Title: Van Allen Probes show the inner radiation zone contains no MeV electrons: ECT/MagEIS data
Abstract: We present Van Allen Probe observations of electrons in the inner radiation zone. The measurements were made by the ECT/MagEIS sensors that were designed to measure electrons with the ability to remove unwanted signals from penetrating protons, providing clean measurements. No electrons >900 keV were observed with equatorial fluxes above background (i.e. >0.1 electrons/(cm2 s sr keV)) in the inner zone. The observed fluxes are compared to the AE9 model and CRRES observations. Electron fluxes <200 keV exceeded the AE9 model 50% fluxes and were lower than the higher energy model fluxes. Phase space density radial profiles for 1.3≤L*<2.5 had mostly positive gradients except near L*~2.1 where the profiles for μ = 20-30 MeV/G were flat or slightly peaked. The major result is that MagEIS data. . .
Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062874 Available at: http://doi.wiley.com/10.1002/2014GL062874
More Details
Authors: Sigsbee K., Kletzing C A, Smith C W, MacDowall Robert, Spence Harlan, et al.
Title: Van Allen Probes, THEMIS, GOES, and Cluster Observations of EMIC waves, ULF pulsations, and an electron flux dropout
Abstract: We examined an electron flux dropout during the 12–14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, THEMIS-A (P5), Cluster 2, and Geostationary Operational Environmental Satellite (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at geosynchronous orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 hours from 12–14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervals of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12–13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He+ EMIC wa. . .
Date: 01/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020877 Available at: http://doi.wiley.com/10.1002/2014JA020877
More Details
Authors: Ni Binbin, Zou Zhengyang, Gu Xudong, Zhou Chen, Thorne Richard M, et al.
Title: Variability of the pitch angle distribution of radiation belt ultra-relativistic electrons during and following intense geomagnetic storms: Van Allen Probes observations
Abstract: Fifteen months of pitch angle resolved Van Allen Probes REPT measurements of differential electron flux are analyzed to investigate the characteristic variability of the pitch angle distribution (PAD) of radiation belt ultra-relativistic (>2 MeV) electrons during storm conditions and during the long-term post-storm decay. By modeling the ultra-relativistic electron pitch angle distribution as sinn α, where α is the equatorial pitch angle, we examine the spatio-temporal variations of the n-value. The results show that in general n-values increase with the level of geomagnetic activity. In principle, ultra-relativistic electrons respond to geomagnetic storms by becoming more peaked at 90° pitch angle with n-values of 2–3 as a supportive signature of chorus acceleration outside the pla. . .
Date: 05/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021065 Available at: http://doi.wiley.com/10.1002/2015JA021065
More Details
Authors: Matsuda Shoya, Kasahara Yoshiya, and Kletzing Craig A.
Title: Variation in crossover frequency of EMIC waves in plasmasphere estimated from ion cyclotron whistler waves observed by Van Allen Probe A
Abstract: We report variations in the propagation of the H+ band ion cyclotron whistlers observed by Van Allen Probe A. Ion cyclotron whistlers are one of the EMIC (electromagnetic ion cyclotron) waves generated by mode conversion from lightning whistlers. Crossover frequency is an important frequency for the ion cyclotron whistlers, which is a function of the variations in the local heavy-ion composition. We surveyed waveform data obtained by the Electric and Magnetic Field Instrument and Integrated Science instrument and found that 3461 H+ band ion cyclotron whistlers were observed from 572 km to 5992 km in altitude. The main finding is that the crossover frequencies of the observed events decreased with increasing altitude. These results support the hypothesis that the total heavy-ion density dec. . .
Date: 01/2016 Publisher: Geophysical Research Letters Pages: 28 - 34 DOI: 10.1002/2015GL066893 Available at: http://doi.wiley.com/10.1002/2015GL066893
More Details
Authors: Malaspina David M., Ripoll Jean-Francois, Chu Xiangning, Hospodarsky George, and Wygant John
Title: Variation in Plasmaspheric Hiss Wave Power With Plasma Density
Abstract: Plasmaspheric hiss waves are commonly observed in the inner magnetosphere. These waves efficiently scatter electrons, facilitating their precipitation into the atmosphere. Predictive inner magnetosphere simulations often model hiss waves using parameterized empirical maps of observed hiss power. These maps nearly always include parameterization by magnetic L value. In this work, data from the Van Allen Probes are used to compare variation in hiss wave power with variation in both L value and cold plasma density. It is found that for L> 2.5, plasmaspheric hiss wave power increases with plasma density. For L> 3, this increase is stronger and occurs regardless of L value and for all local times. This result suggests that the current paradigm for parameterizing hiss wave power in many magnetos. . .
Date: 09/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078564 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078564
More Details
Authors: Pandya Megha, Veenadhari B., Ebihara Y., Kanekal S.G., and Baker D.N.
Title: Variation of Radiation belt electron flux during CME and CIR driven geomagnetic storms: Van Allen Probes observations
Abstract: Relativistic electron flux responses in the inner magnetosphere are investigated for 28 magnetic storms driven by Corotating Interaction Region (CIR) and 27 magnetic storms driven by Coronal Mass Ejection (CME), using data from the Relativistic Electron‐Proton Telescope (REPT) instrument on board Van‐Allen Probes from Oct‐2012 to May‐2017. In this present study we analyze the role of CIRs and CMEs in electron dynamics by sorting the electron fluxes in terms of averaged solar wind parameters, L‐values, and energies. The major outcomes from our study are: (i) At L = 3 and E = 3.4 MeV, for >70% cases the electron flux remains stable, while at L = 5, for ~82% cases it changes with the geomagnetic conditions. (ii) At L = 5, ~53% of the CIR storms and 30% of the CME storms show electro. . .
Date: 07/2019 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2019JA026771 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JA026771
More Details
Authors: Chen Zhe, Chen HongFei, Li YiFan, Xiang HongWen, Yu XiangQian, et al.
Title: Variations of the relativistic electron flux after a magnetospheric compression event
Abstract: On January 21, 2015, a sharp increase of the solar wind dynamic pressure impacted the magnetosphere. The magnetopause moved inward to the region L< 8 without causing a geomagnetic storm. The flux of the relativistic electrons in the outer radiation belt decreased by half during this event based on the observations of the particle radiation monitor (PRM) of the fourth of the China-Brazil Earth Resource Satellites (CBERS-4). The flux remained low for approximately 11 d; it did not recover after a small magnetic storm on January 26 but after a small magnetic storm on February 2. The loss and recovery of the relativistic electrons during this event are investigated using the PRM data, medium- and high-energy electron observations of NOAA-15 and the Van Allen Probes, medium-energy electron obse. . .
Date: 04/2017 Publisher: Science China Technological Sciences Pages: 638 - 647 DOI: 10.1007/s11431-016-9008-3 Available at: https://link.springer.com/article/10.1007/s11431-016-9008-3
More Details
Authors: Ma Q, Artemyev A. V., Mourenas D., Li W, Thorne R M, et al.
Title: Very Oblique Whistler Mode Propagation in the Radiation Belts: Effects of Hot Plasma and Landau Damping
Abstract: Satellite observations of a significant population of very oblique chorus waves in the outer radiation belt have fueled considerable interest in the effects of these waves on energetic electron scattering and acceleration. However, corresponding diffusion rates are extremely sensitive to the refractive index N, controlled by hot plasma effects including Landau damping and wave dispersion modifications by suprathermal (15–100 eV) electrons. A combined investigation of wave and electron distribution characteristics obtained from the Van Allen Probes shows that peculiarities of the measured electron distribution significantly reduce Landau damping, allowing wave propagation with high N ∼ 100–200. Further comparing measured refractive indexes with theoretical estimates incorporating hot . . .
Date: 12/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL075892 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL075892/full
More Details
Authors: Ma Qianli, Mourenas Didier, Li Wen, Artemyev Anton, and Thorne Richard M
Title: VLF waves from ground-based transmitters observed by the Van Allen Probes: Statistical model and effects on plasmaspheric electrons
Abstract: Whistler-mode Very Low Frequency (VLF) waves from powerful ground-based transmitters can resonantly scatter energetic plasmaspheric electrons and precipitate them into the atmosphere. A comprehensive 4-year statistics of Van Allen Probes measurements is carried out to assess their consequences on the dynamics of the inner radiation belt and slot region. Statistical models of the measured wave electric field power and of the inferred full wave magnetic amplitude are provided as a function of L, magnetic local time, season, and Kp over L=1-3, revealing the localization of VLF wave intensity and its variation with geomagnetic activity over 2012-2016. Since this VLF wave model can be directly used together with existing hiss and lightning-generated wave models in radiation belt simulation code. . .
Date: 06/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL073885 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL073885/full
More Details
Authors: Nakayama Y., Ebihara Y., Ohtani S, Gkioulidou M., Takahashi K., et al.
Title: Void structure of O + ions in the inner magnetosphere observed by the Van Allen Probes
Abstract: The Van Allen Probes Helium Oxygen Proton Electron instrument observed a new type of enhancement of O+ ions in the inner magnetosphere during substorms. As the satellite moved outward in the premidnight sector, the flux of the O+ ions with energy ~10 keV appeared first in the energy-time spectrograms. Then, the enhancement of the flux spread toward high and low energies. The enhanced flux of the O+ ions with the highest energy remained, whereas the flux of the ions with lower energy vanished near apogee, forming what we call the void structure. The structure cannot be found in the H+ spectrogram. We studied the generation mechanism of this structure by using numerical simulation. We traced the trajectories of O+ ions in the electric and magnetic fields from the global magnetohydrodynamic. . .
Date: 11/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023013 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023013/full
More Details
Authors: Jahn J -M, Goldstein J, Reeves G D, Fernandes P. A., Skoug R M, et al.
Title: The Warm Plasma Composition in the Inner Magnetosphere during 2012-2015
Abstract: Ionospheric heavy ions play an important role in the dynamics of Earth's magnetosphere. The greater mass and gyro radius of ionospheric oxygen differentiates its behavior from protons at the same energies. Oxygen may have an impact on tail reconnection processes, and it can at least temporarily dominate the energy content of the ring current during geomagnetic storms. At sub-keV energies, multi-species ion populations in the inner magnetosphere form the warm plasma cloak, occupying the energy range between the plasmasphere and the ring current. Lastly, cold lighter ions from the mid-latitude ionosphere create the co-rotating plasmasphere whose outer regions can interact with the plasma cloak, plasma sheet, ring current, and outer electron belt. In this paper we present a statistical view o. . .
Date: 09/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024183 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024183/full
More Details
Authors: Xiao Fuliang, Yang Chang, Su Zhenpeng, Zhou Qinghua, He Zhaoguo, et al.
Title: Wave-driven butterfly distribution of Van Allen belt relativistic electrons
Abstract: Van Allen radiation belts consist of relativistic electrons trapped by Earth's magnetic field. Trapped electrons often drift azimuthally around Earth and display a butterfly pitch angle distribution of a minimum at 90° further out than geostationary orbit. This is usually attributed to drift shell splitting resulting from day–night asymmetry in Earth’s magnetic field. However, direct observation of a butterfly distribution well inside of geostationary orbit and the origin of this phenomenon have not been provided so far. Here we report high-resolution observation that a unusual butterfly pitch angle distribution of relativistic electrons occurred within 5 Earth radii during the 28 June 2013 geomagnetic storm. Simulation results show that combined acceleration by chorus and magnetosoni. . .
Date: 05/2015 Publisher: Nature Communications Pages: 8590 DOI: 10.1038/ncomms9590 Available at: http://www.nature.com/doifinder/10.1038/ncomms9590
More Details
Authors: He Zhaoguo, Yan Qi, Chu Yuchuan, and Cao Yong
Title: Wave-driven gradual loss of energetic electrons in the slot region
Abstract: Resonant pitch angle scattering by plasmaspheric hiss has long been considered to be responsible for the energetic electron loss in the slot region, but the detailed quantitative comparison between theory and observations is still lacking. Here we focus on the loss of 100–600 keV electrons at L = 3 during the recovery phase of a geomagnetic storm on 28 June 2013. Van Allen Probes data showed the concurrence of intense (with power up to 10−4 nT2/Hz) plasmaspheric hiss waves and significant (up to 1 order) loss of energetic electrons within 2 days. Our quasi-linear diffusion simulations show that hiss scattering can basically reproduce the temporal evolution of the angular distribution of the observed electron flux decay. This quantitative analysis provides further support for the mechan. . .
Date: 09/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023087 Available at: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2016JA023087/full
More Details
Authors: Agapitov O. V., Mozer F. S., Artemyev A. V., Mourenas D., and Krasnoselskikh V. V.
Title: Wave-particle interactions in the outer radiation belts
Abstract: Data from the Van Allen Probes have provided the first extensive evidence of non-linear (as opposed to quasi-linear) wave-particle interactions in space, with the associated rapid (fraction of a bounce period) electron acceleration, to hundreds of keV by Landau resonance, in the parallel electric fields of time domain structures (TDS) and very oblique chorus waves. The experimental evidence, simulations, and theories of these processes are discussed.
Date: 12/2015 Publisher: Advances in Astronomy and Space Physics Pages: 68-74 DOI: N/A Available at: http://aasp.kiev.ua/volume5/068-074-Agapitov.pdf
More Details
Authors: Moya Pablo. S., Pinto Víctor A., Viñas Adolfo F., Sibeck David G., Kurth William S., et al.
Title: Weak Kinetic Alfvén Waves Turbulence during the November 14th 2012 geomagnetic storm: Van Allen Probes observations
Abstract: n the dawn sector, L~ 5.5 and MLT~4-7, from 01:30 to 06:00 UT during the November 14th 2012 geomagnetic storm, both Van Allen Probes observed an alternating sequence of locally quiet and disturbed intervals with two strikingly different power fluctuation levels and magnetic field orientations: either small (~10−2 nT2) total power with strong GSM Bx and weak By, or large (~10 nT2) total power with weak Bx, and strong By and Bz components. During both kinds of intervals the fluctuations occur in the vicinity of the local ion gyro-frequencies (0.01-10 Hz) in the spacecraft frame, propagate oblique to the magnetic field, (θ ~ 60°) and have magnetic compressibility C = |δB|||/|δB⊥| ∼ 1, where δB|| (δB⊥) are the average amplitudes of the fluctuations parallel (perpendicular) to the. . .
Date: 06/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020281 Available at: http://doi.wiley.com/10.1002/2014JA020281
More Details
Authors: Boyd A.J., Turner D.L., Reeves G.D., Spence H.E., Baker D.N., et al.
Title: What Causes Radiation Belt Enhancements: A Survey of the Van Allen Probes Era
Abstract: We survey radiation belt enhancement events during the Van Allen Probes era to determine what mechanism is the dominant cause of enhancements and where it is most effective. Two primary mechanisms have been proposed: (1) betatron/Fermi acceleration due to the Earthward radial transport of electrons which produces monotonic gradients in phase space density (PSD) and (2) “local acceleration" due to gyro/Landau resonant interaction with electromagnetic waves which produces radially localized, growing peaks in PSD. To differentiate between these processes, we examine radial profiles of PSD in adiabatic coordinates using data from the Van Allen Probes and THEMIS satellites for 80 outer belt enhancement events from October 2012‐April 2017 This study shows that local acceleration is the domin. . .
Date: 05/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL077699 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL077699
More Details
Authors: Fu Xiangrong, Cowee Misa M., Friedel Reinhard H., Funsten Herbert O, Gary Peter, et al.
Title: Whistler Anisotropy Instabilities as the Source of Banded Chorus: Van Allen Probes Observations and Particle-in-Cell Simulations
Abstract: Magnetospheric banded chorus is enhanced whistler waves with frequencies ωr < Ωe, where Ωe is the electron cyclotron frequency, and a characteristic spectral gap at ωr ≃ Ωe/2. This paper uses spacecraft observations and two-dimensional particle-in-cell (PIC) simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from HOPE instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron mod. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020364 Available at: http://doi.wiley.com/10.1002/2014JA020364
More Details
Authors: Lejosne Solène, and Roederer Juan G.
Title: The “zebra stripes”: An effect of F-region zonal plasma drifts on the longitudinal distribution of radiation belt particles
Abstract: We examine a characteristic effect, namely, the ubiquitous appearance of structured peaks and valleys called zebra stripes in the spectrograms of energetic electrons and ions trapped in the inner belt below L ~ 3. We propose an explanation of this phenomenon as a purely kinematic consequence of particle drift velocity modulation caused by F region zonal plasma drifts in the ionosphere. In other words, we amend the traditional assumption that the electric field associated with ionospheric plasma drives trapped particle distributions into rigid corotation with the Earth. An equation based on a simple first-order model is set up to determine quantitatively the appearance of zebra stripes as a function of magnetic time. Our numerical predictions are in agreement with measurements by the Ra. . .
Date: 01/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021925 Available at: http://doi.wiley.com/10.1002/2015JA021925
More Details
Authors: Li J., Bortnik J., Li W., Ma Q., Thorne R. M., et al.
Title: “Zipper-like” periodic magnetosonic waves: Van Allen Probes, THEMIS, and magnetospheric multiscale observations
Abstract: An interesting form of “zipper-like” magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisat. . .
Date: 01/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023536 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023536
More Details

Pages