Found 70 results
Filters: Author is Wygant, J. R.  [Clear All Filters]
Authors: Liu Si, Xiao Fuliang, Yang Chang, He Yihua, Zhou Qinghua, et al.
Title: Van Allen Probes observations linking radiation belt electrons to chorus waves during 2014 multiple storms
Abstract: During 18 February to 2 March 2014, the Van Allen Probes encountered multiple geomagnetic storms and simultaneously observed intensified chorus and hiss waves. During this period, there were substantial enhancements in fluxes of energetic (53.8 − 108.3 keV) and relativistic (2 − 3.6 MeV) electrons. Chorus waves were excited at locations L = 4 − 6.2 after the fluxes of energetic were greatly enhanced, with a lower frequency band and wave amplitudes ∼ 20 − 100 pT. Strong hiss waves occurred primarily in the main phases or below the location L = 4 in the recovery phases. Relativistic electron fluxes decreased in the main phases due to the adiabatic (e.g., the magnetopause shadowing) or non-adiabatic (hiss-induced scattering) processes. In the recovery phase. . .
Date: 01/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020781 Available at:
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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:
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Authors: Xiao Fuliang, Yang Chang, He Zhaoguo, Su Zhenpeng, Zhou Qinghua, et al.
Title: Chorus acceleration of radiation belt relativistic electrons during March 2013 geomagnetic storm
Abstract: The recent launching of Van Allen probes provides an unprecedent opportunity to investigate variations of the radiation belt relativistic electrons. During the 17–19 March 2013 storm, the Van Allen probes simultaneously detected strong chorus waves and substantial increases in fluxes of relativistic (2 − 4.5 MeV) electrons around L = 4.5. Chorus waves occurred within the lower band 0.1–0.5fce (the electron equatorial gyrofrequency), with a peak spectral density ∼10−4 nT2/Hz. Correspondingly, relativistic electron fluxes increased by a factor of 102–103 during the recovery phase compared to the main phase levels. By means of a Gaussian fit to the observed chorus spectra, the drift and bounce-averaged diffusion coefficients are calculated and then used to solve a 2-D Fokker-Planc. . .
Date: 05/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 3325 - 3332 DOI: 10.1002/2014JA019822 Available at:
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Authors: Malaspina D. M., Ergun R. E., Sturner A., Wygant J R, Bonnell J W, et al.
Title: Chorus waves and spacecraft potential fluctuations: Evidence for wave-enhanced photoelectron escape
Abstract: Chorus waves are important for electron energization and loss in Earth's radiation belts and inner magnetosphere. Because the amplitude and spatial distribution of chorus waves can be strongly influenced by plasma density fluctuations and spacecraft floating potential can be a diagnostic of plasma density, the relationship between measured potential and chorus waves is examined using Van Allen Probes data. While measured potential and chorus wave electric fields correlate strongly, potential fluctuation properties are found not to be consistent with plasma density fluctuations on the timescales of individual chorus wave packets. Instead, potential fluctuations are consistent with enhanced photoelectron escape driven by chorus wave electric fields. Enhanced photoelectron escape may result i. . .
Date: 01/2014 Publisher: Geophysical Research Letters Pages: 236 - 243 DOI: 10.1002/2013GL058769 Available at:
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Authors: Zhou Qinghua, Xiao Fuliang, Yang Chang, Liu Si, Kletzing C A, et al.
Title: Excitation of nightside magnetosonic waves observed by Van Allen Probes
Abstract: During the recovery phase of the geomagnetic storm on 30-31 March 2013, Van Allen Probe A detected enhanced magnetosonic (MS) waves in a broad range of L =1.8-4.7 and MLT =17-22 h, with a frequency range ~10-100 Hz. In the meanwhile, distinct proton ring distributions with peaks at energies of ~10 keV, were also observed in L =3.2-4.6 and L =5.0-5.6. Using a subtracted bi-Maxwellian distribution to model the observed proton ring distribution, we perform three dimensional ray tracing to investigate the instability, propagation and spatial distribution of MS waves. Numerical results show that nightside MS waves are produced by proton ring distribution and grow rapidly from the source location L =5.6 to the location L =5.0, but remain nearly stable at locations L <5.0 Moreover, waves launched. . .
Date: 11/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: n/a - n/a DOI: 10.1002/2014JA020481 Available at:
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Authors: Baker D N, Jaynes A. N., Li X, Henderson M G, Kanekal S G, et al.
Title: Gradual diffusion and punctuated phase space density enhancements of highly relativistic electrons: Van Allen Probes observations
Abstract: The dual-spacecraft Van Allen Probes mission has provided a new window into mega electron volt (MeV) particle dynamics in the Earth's radiation belts. Observations (up to E ~10 MeV) show clearly the behavior of the outer electron radiation belt at different timescales: months-long periods of gradual inward radial diffusive transport and weak loss being punctuated by dramatic flux changes driven by strong solar wind transient events. We present analysis of multi-MeV electron flux and phase space density (PSD) changes during March 2013 in the context of the first year of Van Allen Probes operation. This March period demonstrates the classic signatures both of inward radial diffusive energization and abrupt localized acceleration deep within the outer Van Allen zone (L ~4.0 ± 0.5). Thi. . .
Date: 03/2014 Publisher: Geophysical Research Letters Pages: 1351 - 1358 DOI: 10.1002/2013GL058942 Available at:
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Authors: Baker D N, Jaynes A. N., Hoxie V C, Thorne R M, Foster J. C., et al.
Title: An impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts
Abstract: Early observations1, 2 indicated that the Earth’s Van Allen radiation belts could be separated into an inner zone dominated by high-energy protons and an outer zone dominated by high-energy electrons. Subsequent studies3, 4 showed that electrons of moderate energy (less than about one megaelectronvolt) often populate both zones, with a deep ‘slot’ region largely devoid of particles between them. There is a region of dense cold plasma around the Earth known as the plasmasphere, the outer boundary of which is called the plasmapause. The two-belt radiation structure was explained as arising from strong electron interactions with plasmaspheric hiss just inside the plasmapause boundary5, with the inner edge of the outer radiation zone corresponding to the minimum plasmapause location6. Re. . .
Date: 11/2014 Publisher: Nature Pages: 531 - 534 DOI: 10.1038/nature13956 Available at:
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Authors: Su Zhenpeng, Zhu Hui, Xiao Fuliang, Zheng Huinan, Wang Yuming, et al.
Title: Intense duskside lower band chorus waves observed by Van Allen Probes: Generation and potential acceleration effect on radiation belt electrons
Abstract: Local acceleration driven by whistler mode chorus waves largely accounts for the enhancement of radiation belt relativistic electron fluxes, whose favored region is usually considered to be the plasmatrough with magnetic local time approximately from midnight through dawn to noon. On 2 October 2013, the Van Allen Probes recorded a rarely reported event of intense duskside lower band chorus waves (with power spectral density up to 10−3nT2/Hz) in the low-latitude region outside of L=5. Such chorus waves are found to be generated by the substorm-injected anisotropic suprathermal electrons and have a potentially strong acceleration effect on the radiation belt energetic electrons. This event study demonstrates the possibility of broader spatial regions with effective electron acceleration by. . .
Date: 06/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 4266 - 4273 DOI: 10.1002/jgra.v119.610.1002/2014JA019919 Available at:
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Authors: Hao Y. X., Zong Q.-G., Wang Y. F., Zhou X.-Z., Zhang Hui, et al.
Title: Interactions of energetic electrons with ULF waves triggered by interplanetary shock: Van Allen Probes observations in the magnetotail
Abstract: We present in situ observations of a shock-induced substorm-like event on 13 April 2013 observed by the newly launched Van Allen twin probes. Substorm-like electron injections with energy of 30–500 keV were observed in the region from L∼5.2 to 5.5 immediately after the shock arrival (followed by energetic electron drift echoes). Meanwhile, the electron flux was clearly and strongly varying on the ULF wave time scale. It is found that both toroidal and poloidal mode ULF waves with a period of 150 s emerged following the magnetotail magnetic field reconfiguration after the interplanetary (IP) shock passage. The poloidal mode is more intense than the toroidal mode. The 90° phase shift between the poloidal mode Br and Ea suggests the standing poloidal waves in the Northern Hemisphere. F. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020023 Available at:
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Authors: Malaspina D. M., Andersson L., Ergun R. E., Wygant J R, Bonnell J W, et al.
Title: Nonlinear Electric Field Structures in the Inner Magnetosphere
Abstract: Van Allen Probes observations are presented which demonstrate the presence of nonlinear electric field structures in the inner terrestrial magnetosphere (< 6 RE). A range of structures are observed, including phase space holes and double layers.These structures are observed over several Earth radii in radial distance and over a wide range of magnetic local times. They are observed in the dusk, midnight, and dawn sectors, with the highest concentration pre-midnight. Some nonlinear electric field structures are observed to coincide with dipolarizations of the magnetic field and increases in electron energy flux for energies between 1 keV and 30 keV. Nonlinear electric field structures possess isolated impulsive electric fields, often with a significant component parallel to the ambient m. . .
Date: 08/2014 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL061109 Available at:
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Authors: Foster J. C., Erickson P. J., Baker D N, Claudepierre S G, Kletzing C A, et al.
Title: Prompt energization of relativistic and highly relativistic electrons during a substorm interval: Van Allen Probes observations
Abstract: On 17 March 2013, a large magnetic storm significantly depleted the multi-MeV radiation belt. We present multi-instrument observations from the Van Allen Probes spacecraft Radiation Belt Storm Probe A and Radiation Belt Storm Probe B at ~6 Re in the midnight sector magnetosphere and from ground-based ionospheric sensors during a substorm dipolarization followed by rapid reenergization of multi-MeV electrons. A 50% increase in magnetic field magnitude occurred simultaneously with dramatic increases in 100 keV electron fluxes and a 100 times increase in VLF wave intensity. The 100 keV electrons and intense VLF waves provide a seed population and energy source for subsequent radiation belt enhancements. Highly relativistic (>2 MeV) electron fluxes increased immediately at L* ~ 4.5. . .
Date: 01/2014 Publisher: Geophysical Research Letters Pages: 20 - 25 DOI: 10.1002/2013GL058438 Available at:
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Authors: Foster J. C., Erickson P. J., Coster A. J., Thaller S., Tao J., et al.
Title: Storm time observations of plasmasphere erosion flux in the magnetosphere and ionosphere
Abstract: Plasmasphere erosion carries cold dense plasma of ionospheric origin in a storm-enhanced density plume extending from dusk toward and through the noontime cusp and dayside magnetopause and back across polar latitudes in a polar tongue of ionization. We examine dusk sector (20 MLT) plasmasphere erosion during the 17 March 2013 storm (Dst ~ −130 nT) using simultaneous, magnetically aligned direct sunward ion flux observations at high altitude by Van Allen Probes RBSP-A (at ~3.0 Re) and at ionospheric heights (~840 km) by DMSP F-18. Plasma erosion occurs at both high and low altitudes where the subauroral polarization stream flow overlaps the outer plasmasphere. At ~20 UT, RBSP-A observed ~1.2E12 m−2 s−1 erosion flux, while DMSP F-18 observed ~2E13 m−2 s−1 sunward flux. We. . .
Date: 02/2014 Publisher: Geophysical Research Letters Pages: 762 - 768 DOI: 10.1002/2013GL059124 Available at:
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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:
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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:
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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:
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Authors: Wygant J R, Bonnell J W, Goetz K, Ergun R E, Mozer F S, et al.
Title: The Electric Field and Waves (EFW) Instruments on the Radiation Belt Storm Probes Mission
Abstract: The Electric Fields and Waves (EFW) Instruments on the two Radiation Belt Storm Probe (RBSP) spacecraft (recently renamed the Van Allen Probes) are designed to measure three dimensional quasi-static and low frequency electric fields and waves associated with the major mechanisms responsible for the acceleration of energetic charged particles in the inner magnetosphere of the Earth. For this measurement, the instrument uses two pairs of spherical double probe sensors at the ends of orthogonal centripetally deployed booms in the spin plane with tip-to-tip separations of 100 meters. The third component of the electric field is measured by two spherical sensors separated by ∼15 m, deployed at the ends of two stacer booms oppositely directed along the spin axis of the spacecraft. The instrume. . .
Date: 11/2013 Publisher: Space Science Reviews DOI: 10.1007/s11214-013-0013-7 Available at:
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Authors: Dai L, Takahashi K, Wygant J R, Chen L, Bonnell J W, et al.
Title: Excitation of Poloidal standing Alfven waves through the drift resonance wave-particle interaction
Abstract: Drift-resonance wave-particle interaction is a fundamental collisionless plasma process studied extensively in theory. Using cross-spectral analysis of electric field, magnetic field, and ion flux data from the Van Allen Probe (Radiation Belt Storm Probes) spacecraft, we present direct evidence identifying the generation of a fundamental mode standing poloidal wave through drift-resonance interactions in the inner magnetosphere. Intense azimuthal electric field (Eφ) oscillations as large as 10mV/m are observed, associated with radial magnetic field (Br) oscillations in the dawn-noon sector near but south of the magnetic equator at L∼5. The observed wave period, Eφ/Br ratio and the 90° phase lag between Br and Eφ are all consistent with fundamental mode standing Poloidal waves. Phase . . .
Date: 08/2013 Publisher: Geophysical Research Letters DOI: 10.1002/grl.50800 Available at:
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Authors: Li W, Thorne R M, Bortnik J, Reeves G D, Kletzing C A, et al.
Title: An unusual enhancement of low-frequency plasmaspheric hiss in the outer plasmasphere associated with substorm-injected electrons
Abstract: Both plasmaspheric hiss and chorus waves were observed simultaneously by the two Van Allen Probes in association with substorm-injected energetic electrons. Probe A, located inside the plasmasphere in the postdawn sector, observed intense plasmaspheric hiss, whereas Probe B observed chorus waves outside the plasmasphere just before dawn. Dispersed injections of energetic electrons were observed in the dayside outer plasmasphere associated with significant intensification of plasmaspheric hiss at frequencies down to ~20 Hz, much lower than typical hiss wave frequencies of 100–2000 Hz. In the outer plasmasphere, the upper energy of injected electrons agrees well with the minimum cyclotron resonant energy calculated for the lower cutoff frequency of the observed hiss, and computed conve. . .
Date: 08/2013 Publisher: Geophysical Research Letters Pages: 3798 - 3803 DOI: 10.1002/grl.50787 Available at:
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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:
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Authors: Li Xinlin, Roth I, Temerin M, Wygant J R, Hudson M K, et al.
Title: Simulation of the prompt energization and transport of radiation belt particles during the March 24, 1991 SSC
Abstract: We model the rapid (∼ 1 min) formation of a new electron radiation belt at L ≃ 2.5 that resulted from the Storm Sudden Commencement (SSC) of March 24, 1991 as observed by the CRRES satellite. Guided by the observed electric and magnetic fields, we represent the time-dependent magnetospheric electric field during the SSC by an asymmetric bipolar pulse that is associated with the compression and relaxation of the Earth's magnetic field. We follow the electrons using a relativistic guiding center code. The test-particle simulations show that electrons with energies of a few MeV at L > 6 were energized up to 40 MeV and transported to L ≃ 2.5 during a fraction of their drift period. The energization process conserves the first adiabatic invariant and is enhanced due to resonance of the el. . .
Date: 11/1993 Publisher: Geophysical Research Letters Pages: 2423–2426 DOI: 10.1029/93GL02701 Available at:
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