Biblio

Found 134 results
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2016
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: Hao Y. X., Zong Q.-G., Zhou X.-Z., Fu S. Y., Rankin R, et al.
Title: Electron dropout echoes induced by interplanetary shock: Van Allen Probes observations
Abstract: On 23 November 2012, a sudden dropout of the relativistic electron flux was observed after an interplanetary shock arrival. The dropout peaks at ∼1MeV and more than 80% of the electrons disappeared from the drift shell. Van Allen twin Probes observed a sharp electron flux dropout with clear energy dispersion signals. The repeating flux dropout and recovery signatures, or “dropout echoes”, constitute a new phenomenon referred to as a “drifting electron dropout” with a limited initial spatial range. The azimuthal range of the dropout is estimated to be on the duskside, from ∼1300 to 0100 LT. We conclude that the shock-induced electron dropout is not caused by the magnetopause shadowing. The dropout and consequent echoes suggest that the radial migration of relativistic electrons . . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL069140 Available at: http://doi.wiley.com/10.1002/2016GL069140h
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Authors: Turner D. L., Fennell J. F., Blake J B, Clemmons J. H., Mauk B H, et al.
Title: Energy limits of electron acceleration in the plasma sheet during substorms: A case study with the Magnetospheric Multiscale (MMS) mission
Abstract: We present multipoint observations of earthward moving dipolarization fronts and energetic particle injections from NASA's Magnetospheric Multiscale mission with a focus on electron acceleration. From a case study during a substorm on 02 August 2015, we find that electrons are only accelerated over a finite energy range, from a lower energy threshold at ~7–9 keV up to an upper energy cutoff in the hundreds of keV range. At energies lower than the threshold energy, electron fluxes decrease, potentially due to precipitation by strong parallel electrostatic wavefields or initial sources in the lobes. Electrons at energies higher than the threshold are accelerated cumulatively by a series of impulsive magnetic dipolarization events. This case demonstrates how the upper energy cutoff increa. . .
Date: 08/2016 Publisher: Geophysical Research Letters Pages: 7785 - 7794 DOI: 10.1002/2016GL069691 Available at: http://doi.wiley.com/10.1002/2016GL069691
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Authors: Zhou Qinghua, Xiao Fuliang, Yang Chang, Liu Si, He Yihua, et al.
Title: Evolution of chorus emissions into plasmaspheric hiss observed by Van Allen Probes
Abstract: The two classes of whistler mode waves (chorus and hiss) play different roles in the dynamics of radiation belt energetic electrons. Chorus can efficiently accelerate energetic electrons, and hiss is responsible for the loss of energetic electrons. Previous studies have proposed that chorus is the source of plasmaspheric hiss, but this still requires an observational confirmation because the previously observed chorus and hiss emissions were not in the same frequency range in the same time. Here we report simultaneous observations form Van Allen Probes that chorus and hiss emissions occurred in the same range ∼300–1500 Hz with the peak wave power density about 10−5 nT2/Hz during a weak storm on 3 July 2014. Chorus emissions propagate in a broad region outside the plasmapause. Meanwhi. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 4518 - 4529 DOI: 10.1002/2016JA022366 Available at: http://doi.wiley.com/10.1002/2016JA022366
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Authors: Mann I. R., Ozeke L. G., Murphy K. R., Claudepierre S G, Turner D. L., et al.
Title: Explaining the dynamics of the ultra-relativistic third Van Allen radiation belt
Abstract: Since the discovery of the Van Allen radiation belts over 50 years ago, an explanation for their complete dynamics has remained elusive. Especially challenging is understanding the recently discovered ultra-relativistic third electron radiation belt. Current theory asserts that loss in the heart of the outer belt, essential to the formation of the third belt, must be controlled by high-frequency plasma wave–particle scattering into the atmosphere, via whistler mode chorus, plasmaspheric hiss, or electromagnetic ion cyclotron waves. However, this has failed to accurately reproduce the third belt. Using a datadriven, time-dependent specification of ultra-low-frequency (ULF) waves we show for the first time how the third radiation belt is established as a simple, elegant consequence o. . .
Date: 06/2016 Publisher: Nature Physics DOI: 10.1038/nphys3799 Available at: http://www.nature.com/doifinder/10.1038/nphys3799
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Authors: Yu J., Li L.Y., Cao J. B., Reeves G D, Baker D N, et al.
Title: The influences of solar wind pressure and interplanetary magnetic field on global magnetic field and outer radiation belt electrons
Abstract: Using the Van Allen Probe in-situ measured magnetic field and electron data, we examine the solar wind dynamic pressure and interplanetary magnetic field (IMF) effects on global magnetic field and outer radiation belt relativistic electrons (≥1.8 MeV). The dynamic pressure enhancements (>2nPa) cause the dayside magnetic field increase and the nightside magnetic field reduction, whereas the large southward IMFs (Bz-IMF < -2nT) mainly lead to the decrease of the nightside magnetic field. In the dayside increased magnetic field region (MLT ~ 06:00 - 18:00, and L > 4), the pitch angles of relativistic electrons are mainly pancake distributions with a flux peak around 90o (corresponding anisotropic index A > 0.1), and the higher-energy electrons have stronger pancake distrib. . .
Date: 06/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL069029 Available at: http://doi.wiley.com/10.1002/2016GL069029
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Authors: Turner D. L., O'Brien T P, Fennell J. F., Claudepierre S G, Blake J B, et al.
Title: Investigating the source of near-relativistic and relativistic electrons in Earth's inner radiation belt
Abstract: Using observations from NASA's Van Allen Probes, we study the role of sudden particle enhancements at low L-shells (SPELLS) as a source of inner radiation belt electrons. SPELLS events are characterized by electron intensity enhancements of approximately an order of magnitude or more in less than one day at L < 3. During quiet and average geomagnetic conditions, the phase space density radial distributions for fixed first and second adiabatic invariants are peaked at 2 < L < 3 for electrons ranging in energy from ~50 keV to ~1 MeV, indicating that slow inward radial diffusion is not the dominant source of inner belt electrons under quiet/average conditions. During SPELLS events, the evolution of electron distributions reveals an enhancement of phase space density that can excee. . .
Date: 12/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023600 Available at: http://doi.wiley.com/10.1002/2016JA023600
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Authors: Xia Zhiyang, Chen Lunjin, Dai Lei, Claudepierre Seth G., Chan Anthony A, et al.
Title: Modulation of chorus intensity by ULF waves deep in the inner magnetosphere
Abstract: Previous studies have shown that chorus wave intensity can be modulated by Pc4-Pc5 compressional ULF waves. In this study, we present Van Allen Probes observation of ULF wave modulating chorus wave intensity, which occurred deep in the magnetosphere. The ULF wave shows fundamental poloidal mode signature and mirror mode compressional nature. The observed ULF wave can modulate not only the chorus wave intensity but also the distribution of both protons and electrons. Linear growth rate analysis shows consistence with observed chorus intensity variation at low frequency (f <∼ 0.3fce), but cannot account for the observed higher-frequency chorus waves, including the upper band chorus waves. This suggests the chorus waves at higher-frequency ranges require nonlinear mechanisms. In addition, w. . .
Date: 09/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL070280 Available at: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2016GL070280/full
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Authors: Su Zhenpeng, Gao Zhonglei, Zhu Hui, Li Wen, Zheng Huinan, et al.
Title: Nonstorm time dropout of radiation belt electron fluxes on 24 September 2013
Abstract: Radiation belt electron flux dropouts during the main phase of geomagnetic storms have received increasing attention in recent years. Here we focus on a rarely reported nonstorm time dropout event observed by Van Allen Probes on 24 September 2013. Within several hours, the radiation belt electron fluxes exhibited a significant (up to 2 orders of magnitude) depletion over a wide range of radial distances (L > 4.5), energies (∼500 keV to several MeV) and equatorial pitch angles (0°≤αe≤180°). STEERB simulations show that the relativistic electron loss in the region L = 4.5–6.0 was primarily caused by the pitch angle scattering of observed plasmaspheric hiss and electromagnetic ion cyclotron waves. Our results emphasize the complexity of radiation belt dynamics and the importance of. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022546 Available at: http://doi.wiley.com/10.1002/2016JA022546
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Authors: Zhang X.-J., Li W, Thorne R M, Angelopoulos V, Ma Q, et al.
Title: Physical mechanism causing rapid changes in ultrarelativistic electron pitch angle distributions right after a shock arrival: Evaluation of an electron dropout event
Abstract: Three mechanisms have been proposed to explain relativistic electron flux depletions (dropouts) in the Earth's outer radiation belt during storm times: adiabatic expansion of electron drift shells due to a decrease in magnetic field strength, magnetopause shadowing and subsequent outward radial diffusion, and precipitation into the atmosphere (driven by EMIC wave scattering). Which mechanism predominates in causing electron dropouts commonly observed in the outer radiation belt is still debatable. In the present study, we evaluate the physical mechanism that may be primarily responsible for causing the sudden change in relativistic electron pitch angle distributions during a dropout event observed by Van Allen Probes during the main phase of the 27 February 2014 storm. During this event, t. . .
Date: 09/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022517 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA022517/abstract
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Authors: Kanekal S G, Baker D N, Fennell J. F., Jones A., Schiller Q., et al.
Title: Prompt acceleration of magnetospheric electrons to ultrarelativistic energies by the 17 March 2015 interplanetary shock
Abstract: Trapped electrons in Earth's outer Van Allen radiation belt are influenced profoundly by solar phenomena such as high-speed solar wind streams, coronal mass ejections (CME), and interplanetary (IP) shocks. In particular, strong IP shocks compress the magnetosphere suddenly and result in rapid energization of electrons within minutes. It is believed that the electric fields induced by the rapid change in the geomagnetic field are responsible for the energization. During the latter part of March 2015, a CME impact led to the most powerful geomagnetic storm (minimum Dst = −223 nT at 17 March, 23 UT) observed not only during the Van Allen Probe era but also the entire preceding decade. Magnetospheric response in the outer radiation belt eventually resulted in elevated levels of energized ele. . .
Date: 08/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 7622 - 7635 DOI: 10.1002/2016JA022596 Available at: http://doi.wiley.com/10.1002/2016JA022596
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Authors: Li W, Ma Q, Thorne R M, Bortnik J, Zhang X.-J., et al.
Title: Radiation belt electron acceleration during the 17 March 2015 geomagnetic storm: Observations and simulations
Abstract: Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3-D diffusion simulation. By quantitatively comparing the observed and simulated electron evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak loca. . .
Date: 06/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 5520 - 5536 DOI: 10.1002/jgra.v121.610.1002/2016JA022400 Available at: http://doi.wiley.com/10.1002/2016JA022400
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Authors: Jordanova V K, Tu W., Chen Y., Morley S. K., Panaitescu A.-D., et al.
Title: RAM-SCB simulations of electron transport and plasma wave scattering during the October 2012 “double-dip” storm
Abstract: Mechanisms for electron injection, trapping, and loss in the near-Earth space environment are investigated during the October 2012 “double-dip” storm using our ring current-atmosphere interactions model with self-consistent magnetic field (RAM-SCB). Pitch angle and energy scattering are included for the first time in RAM-SCB using L and magnetic local time (MLT)-dependent event-specific chorus wave models inferred from NOAA Polar-orbiting Operational Environmental Satellites (POES) and Van Allen Probes Electric and Magnetic Field Instrument Suite and Integrated Science observations. The dynamics of the source (approximately tens of keV) and seed (approximately hundreds of keV) populations of the radiation belts simulated with RAM-SCB is compared with Van Allen Probes Magnetic Electron . . .
Date: 09/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022470 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA022470/abstract
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Authors: Goldstein J, Baker D N, Blake J B, De Pascuale S., Funsten H O, et al.
Title: The relationship between the plasmapause and outer belt electrons
Abstract: We quantify the spatial relationship between the plasmapause and outer belt electrons for a 5 day period, 15–20 January 2013, by comparing locations of relativistic electron flux peaks to the plasmapause. A peak-finding algorithm is applied to 1.8–7.7 MeV relativistic electron flux data. A plasmapause gradient finder is applied to wave-derived electron number densities >10 cm−3. We identify two outer belts. Outer belt 1 is a stable zone of >3 MeV electrons located 1–2 RE inside the plasmapause. Outer belt 2 is a dynamic zone of <3 MeV electrons within 0.5 RE of the moving plasmapause. Electron fluxes earthward of each belt's peak are anticorrelated with cold plasma density. Belt 1 decayed on hiss timescales prior to a disturbance on 17 January and suffered only a modest dropout, pe. . .
Date: 08/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023046 Available at: http://doi.wiley.com/10.1002/2016JA023046
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Authors: Zhao H., Li X, Baker D N, Claudepierre S G, Fennell J. F., et al.
Title: Ring current electron dynamics during geomagnetic storms based on the Van Allen Probes measurements
Abstract: Based on comprehensive measurements from Helium, Oxygen, Proton, and Electron Mass Spectrometer Ion Spectrometer, Relativistic Electron-Proton Telescope, and Radiation Belt Storm Probes Ion Composition Experiment instruments on the Van Allen Probes, comparative studies of ring current electrons and ions are performed and the role of energetic electrons in the ring current dynamics is investigated. The deep injections of tens to hundreds of keV electrons and tens of keV protons into the inner magnetosphere occur frequently; after the injections the electrons decay slowly in the inner belt but protons in the low L region decay very fast. Intriguing similarities between lower energy protons and higher-energy electrons are also found. The evolution of ring current electron and ion energy densi. . .
Date: 04/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 3333 - 3346 DOI: 10.1002/2016JA022358 Available at: http://doi.wiley.com/10.1002/2016JA022358
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Authors: Ma Q, Li W, Thorne R M, Nishimura Y., Zhang X.-J., et al.
Title: Simulation of energy-dependent electron diffusion processes in the Earth's outer radiation belt
Abstract: The radial and local diffusion processes induced by various plasma waves govern the highly energetic electron dynamics in the Earth's radiation belts, causing distinct characteristics in electron distributions at various energies. In this study, we present our simulation results of the energetic electron evolution during a geomagnetic storm using the University of California, Los Angeles 3-D diffusion code. Following the plasma sheet electron injections, the electrons at different energy bands detected by the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron Proton Telescope (REPT) instruments on board the Van Allen Probes exhibit a rapid enhancement followed by a slow diffusive movement in differential energy fluxes, and the radial extent to which electrons can penetra. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022507 Available at: http://doi.wiley.com/10.1002/2016JA022507
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Authors: Boyd A.J., Spence H.E., Huang C.-L., Reeves G D, Baker D N, et al.
Title: Statistical Properties of the Radiation Belt Seed Population
Abstract: We present a statistical analysis of phase space density data from the first 26 months of the Van Allen Probes mission. In particular we investigate the relationship between the 10s-100s keV seed electrons and >1 MeV core radiation belt electron population. Using a cross correlation analysis, we find that the seed and core populations are well correlated with a coefficient of ≈ 0.73 with a time lag of 10-15 hours. We present evidence of a seed population threshold that is necessary for subsequent acceleration. The depth of penetration of the seed population determines the inner boundary of the acceleration process. However, we show that an enhanced seed population alone is not enough to produce acceleration in the higher energies, implying that the seed population of 100s of keV electron. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022652 Available at: http://doi.wiley.com/10.1002/2016JA022652
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Authors: Ripoll J. F., Loridan V., Cunningham G. S., Reeves G D, and Shprits Y Y
Title: On the Time Needed to Reach an Equilibrium Structure of the Radiation Belts
Abstract: In this study, we complement the notion of equilibrium states of the radiation belts with a discussion on the dynamics and time needed to reach equilibrium. We solve for the equilibrium states obtained using 1D radial diffusion with recently developed hiss and chorus lifetimes at constant values of Kp = 1, 3 and 6. We find that the equilibrium states at moderately low Kp, when plotted vs L-shell (L) and energy (E), display the same interesting S-shape for the inner edge of the outer belt as recently observed by the Van Allen Probes. The S-shape is also produced as the radiation belts dynamically evolve toward the equilibrium state when initialized to simulate the buildup after a massive dropout or to simulate loss due to outward diffusion from a saturated state. Physically, this shape,. . .
Date: 06/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA022207 Available at: http://doi.wiley.com/10.1002/2015JA022207
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Authors: Li W, Mourenas D., Artemyev A. V., Bortnik J, Thorne R M, et al.
Title: Unraveling the excitation mechanisms of highly oblique lower band chorus waves
Abstract: Excitation mechanisms of highly oblique, quasi-electrostatic lower band chorus waves are investigated using Van Allen Probes observations near the equator of the Earth's magnetosphere. Linear growth rates are evaluated based on in situ, measured electron velocity distributions and plasma conditions and compared with simultaneously observed wave frequency spectra and wave normal angles. Accordingly, two distinct excitation mechanisms of highly oblique lower band chorus have been clearly identified for the first time. The first mechanism relies on cyclotron resonance with electrons possessing both a realistic temperature anisotropy at keV energies and a plateau at 100–500 eV in the parallel velocity distribution. The second mechanism corresponds to Landau resonance with a 100–500 eV . . .
Date: 09/2016 Publisher: Geophysical Research Letters Pages: 8867 - 8875 DOI: 10.1002/grl.v43.1710.1002/2016GL070386 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL070386/abstract
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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
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2015
Authors: Claudepierre S G, O'Brien T P, Blake J B, Fennell J. F., Roeder J. L., et al.
Title: A background correction algorithm for Van Allen Probes MagEIS electron flux measurements
Abstract: We describe an automated computer algorithm designed to remove background contamination from the Van Allen Probes MagEIS electron flux measurements. We provide a detailed description of the algorithm with illustrative examples from on-orbit data. We find two primary sources of background contamination in the MagEIS electron data: inner zone protons and bremsstrahlung X-rays generated by energetic electrons interacting with the spacecraft material. Bremsstrahlung X-rays primarily produce contamination in the lower energy MagEIS electron channels (~30-500 keV) and in regions of geospace where multi-MeV electrons are present. Inner zone protons produce contamination in all MagEIS energy channels at roughly L < 2.5. The background corrected MagEIS electron data produce a more accurate me. . .
Date: 06/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021171 Available at: http://doi.wiley.com/10.1002/2015JA021171
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Authors: Hwang J., Choi E.-J., Park J.-S., Fok M.-C., Lee D.-Y., et al.
Title: Comprehensive analysis of the flux dropout during 7-8 November 2008 storm using multi-satellites observations and RBE model
Abstract: We investigate an electron flux dropout during a weak storm on 7–8 November 2008, with Dst minimum value being −37 nT. During this period, two clear dropouts were observed on GOES 11 > 2 MeV electrons. We also find a simultaneous dropout in the subrelativistic electrons recorded by Time History of Events and Macroscale Interactions during Substorms probes in the outer radiation belt. Using the Radiation Belt Environment model, we try to reproduce the observed dropout features in both relativistic and subrelativistic electrons. We found that there are local time dependences in the dropout for both observation and simulation in subrelativistic electrons: (1) particle loss begins from nightside and propagates into dayside and (2) resupply starts from near dawn magnetic local time . . .
Date: 05/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021085 Available at: http://doi.wiley.com/10.1002/2015JA021085
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Authors: Jaynes A. N., Lessard M. R., Takahashi K., Ali A. F., Malaspina D. M., et al.
Title: Correlated Pc4-5 ULF waves, whistler-mode chorus and pulsating aurora observed by the Van Allen Probes and ground-based systems
Abstract: Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch-angle scattering of 10's keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and 10's keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4-5 compressional pulsations and modulation of whistler-mode chorus using THEMIS. In the current study, we present simultaneous in-situ observations of structured chorus waves and an apparent field line resonance (in the Pc4-5 range) as a result of a substorm injection, observed by Van Allen Probes, along with groun. . .
Date: 07/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021380 Available at: http://doi.wiley.com/10.1002/2015JA021380
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Authors: Su Zhenpeng, Zhu Hui, Xiao Fuliang, Zheng Huinan, Wang Yuming, et al.
Title: Disappearance of plasmaspheric hiss following interplanetary shock
Abstract: Plasmaspheric hiss is one of the important plasma waves controlling radiation belt dynamics. Its spatiotemporal distribution and generation mechanism are presently the object of active research. We here give the first report on the shock-induced disappearance of plasmaspheric hiss observed by the Van Allen Probes on 8 October 2013. This special event exhibits the dramatic variability of plasmaspheric hiss and provides a good opportunity to test its generation mechanisms. The origination of plasmaspheric hiss from plasmatrough chorus is suggested to be an appropriate prerequisite to explain this event. The shock increased the suprathermal electron fluxes, and then the enhanced Landau damping promptly prevented chorus waves from entering the plasmasphere. Subsequently, the shrinking magnetop. . .
Date: 03/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL063906 Available at: http://doi.wiley.com/10.1002/2015GL063906
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Authors: Turner D. L., Claudepierre S G, Fennell J. F., O'Brien T P, Blake J B, et al.
Title: Energetic electron injections deep into the inner magnetosphere associated with substorm activity
Abstract: From a survey of the first nightside season of NASA's Van Allen Probes mission (Dec/2012 – Sep/2013), 47 energetic (10s to 100s of keV) electron injection events were found at L-shells ≤ 4, all of which are deeper than any previously reported substorm-related injections. Preliminary details from these events are presented, including how: all occurred shortly after dipolarization signatures and injections were observed at higher L-shells; the deepest observed injection was at L~2.5; and, surprisingly, L≤4 injections are limited in energy to ≤250 keV. We present a detailed case study of one example event revealing that the injection of electrons down to L~3.5 was different from injections observed at higher L and likely resulted from drift resonance with a fast magnetosonic wave in t. . .
Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL063225 Available at: http://doi.wiley.com/10.1002/2015GL063225
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Authors: Zhao H., Li X, Baker D N, Fennell J. F., Blake J B, et al.
Title: The evolution of ring current ion energy density and energy content during geomagnetic storms based on Van Allen Probes measurements
Abstract: Enabled by the comprehensive measurements from the MagEIS, HOPE, and RBSPICE instruments onboard Van Allen Probes in the heart of the radiation belt, the relative contributions of ions with different energies and species to the ring current energy density and their dependence on the phases of geomagnetic storms are quantified. The results show that lower energy (<50 keV) protons enhance much more often and also decay much faster than higher energy protons. During the storm main phase, ions with energies < 50 keV contribute more significantly to the ring current than those with higher energies; while the higher energy protons dominate during the recovery phase and quiet times. The enhancements of higher energy proton fluxes as well as energy content generally occur later than those of lower. . .
Date: 08/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021533 Available at: http://doi.wiley.com/10.1002/2015JA021533
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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: Motoba T., Ohtani S, Anderson B J, Korth H., Mitchell D., et al.
Title: On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations
Abstract: Magnetotail processes and structures related to substorm growth phase/onset auroral arcs remain poorly understood mostly due to the lack of adequate observations. In this study we make a comparison between ground-based optical measurements of the premidnight growth phase/onset arcs at subauroral latitudes and magnetically conjugate measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) at ~780 km in altitude and by the Van Allen Probe B (RBSP-B) spacecraft crossing L values of ~5.0–5.6 in the premidnight inner tail region. The conjugate observations offer a unique opportunity to examine the detailed features of the arc location relative to large-scale Birkeland currents and of the magnetospheric counterpart. Our main findings include (1. . .
Date: 10/2015 Publisher: Journal of Geophysical Research: Space Physics Pages: 8707 - 8722 DOI: 10.1002/jgra.v120.1010.1002/2015JA021676 Available at: http://doi.wiley.com/10.1002/jgra.v120.10http://doi.wiley.com/10.1002/2015JA021676http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015JA021676
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Authors: Nosé M., Oimatsu S., Keika K, Kletzing C A, Kurth W S, et al.
Title: Formation of the oxygen torus in the inner magnetosphere: Van Allen Probes observations
Abstract: We study the formation process of an oxygen torus during the 12–15 November 2012 magnetic storm, using the magnetic field and plasma wave data obtained by Van Allen Probes. We estimate the local plasma mass density (ρL) and the local electron number density (neL) from the resonant frequencies of standing Alfvén waves and the upper hybrid resonance band. The average ion mass (M) can be calculated by M ∼ ρL/neL under the assumption of quasi-neutrality of plasma. During the storm recovery phase, both Probe A and Probe B observe the oxygen torus at L = 3.0–4.0 and L = 3.7–4.5, respectively, on the morning side. The oxygen torus has M = 4.5–8 amu and extends around the plasmapause that is identified at L∼3.2–3.9. We find that during the initial phase, M is 4–7 amu throughout . . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020593 Available at: http://doi.wiley.com/10.1002/2014JA020593
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Authors: Hwang K.-J., Sibeck D G, Fok M.-C. H., Zheng Y., Nishimura Y., et al.
Title: The global context of the 14 November, 2012 storm event
Abstract: From 2 to 5 UT on 14 November, 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ~20–30 min prior to. . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020826 Available at: http://doi.wiley.com/10.1002/2014JA020826
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Authors: Posch J. L, Engebretson M. J., Olson C. N., Thaller S. A., Breneman A. W., et al.
Title: Low-harmonic magnetosonic waves observed by the Van Allen Probes
Abstract: Purely compressional electromagnetic waves (fast magnetosonic waves), generated at multiple harmonics of the local proton gyrofrequency, have been observed by various types of satellite instruments (fluxgate and search coil magnetometers and electric field sensors), but most recent studies have used data from search coil sensors, and many have been restricted to high harmonics. We report here on a survey of low-harmonic waves, based on electric and magnetic field data from the EFW double probe and EMFISIS fluxgate magnetometer instruments, respectively, on the Van Allen Probes spacecraft during its first full precession through all local times, from October 1, 2012 through July 13, 2014. These waves were observed both inside and outside the plasmapause (PP), at L shells from 2.4 to ~6 (the. . .
Date: 07/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021179 Available at: http://doi.wiley.com/10.1002/2015JA021179
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Authors: Ma Q, Li W, Thorne R M, Ni B, Kletzing C A, et al.
Title: Modeling inward diffusion and slow decay of energetic electrons in the Earth's outer radiation belt
Abstract: A new 3D diffusion code is used to investigate the inward intrusion and slow decay of energetic radiation belt electrons (>0.5 MeV) observed by the Van Allen Probes during a 10-day quiet period in March 2013. During the inward transport the peak differential electron fluxes decreased by approximately an order of magnitude at various energies. Our 3D radiation belt simulation including radial diffusion and pitch angle and energy diffusion by plasmaspheric hiss and Electromagnetic Ion Cyclotron (EMIC) waves reproduces the essential features of the observed electron flux evolution. The decay timescales and the pitch angle distributions in our simulation are consistent with the Van Allen Probes observations over multiple energy channels. Our study suggests that the quiet-time energetic electro. . .
Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062977 Available at: http://doi.wiley.com/10.1002/2014GL062977
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Authors: Yu J., Li L.Y., Cao J. B., Yuan Z. G., Reeves G D, et al.
Title: Multiple loss processes of relativistic electrons outside the heart of outer radiation belt during a storm sudden commencement
Abstract: By examining the compression-induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP-A/B), we find that the relativistic electrons (>2MeV) outside the heart of outer radiation belt (L*≥ 5) undergo multiple losses during a storm sudden commencement (SSC). The relativistic electron loss mainly occurs in the field-aligned direction (pitch angle α< 30° or >150°), and the flux decay of the field-aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30°-150° increase (decrease) with the decreasing (increasing) geocentric distance (|ΔL|< 0.25) of the RBSP-B (RBSP-A) location, and the electron fluxes in the quasi-. . .
Date: 11/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021460 Available at: http://doi.wiley.com/10.1002/2015JA021460http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015JA021460
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Authors: Xiao Fuliang, Zhou Qinghua, He Yihua, Yang Chang, Liu Si, et al.
Title: Penetration of magnetosonic waves into the plasmasphere observed by the Van Allen Probes
Abstract: During the small storm on 14–15 April 2014, Van Allen Probe A measured a continuously distinct proton ring distribution and enhanced magnetosonic (MS) waves along its orbit outside the plasmapause. Inside the plasmasphere, strong MS waves were still present but the distinct proton ring distribution was falling steeply with distance. We adopt a sum of subtracted bi-Maxwellian components to model the observed proton ring distribution and simulate the wave trajectory and growth. MS waves at first propagate toward lower L shells outside the plasmasphere, with rapidly increasing path gains related to the continuous proton ring distribution. The waves then gradually cross the plasmapause into the deep plasmasphere, with almost unchanged path gains due to the falling proton ring distribution an. . .
Date: 09/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL065745 Available at: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015GL065745/full
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Authors: Zhu Hui, Su Zhenpeng, Xiao Fuliang, Zheng Huinan, Wang Yuming, et al.
Title: Plasmatrough exohiss waves observed by Van Allen Probes: Evidence for leakage from plasmasphere and resonant scattering of radiation belt electrons
Abstract: Exohiss waves are whistler mode hiss observed in the plasmatrough region. We present a case study of exohiss waves and the corresponding background plasma distributions observed by the Van Allen Probes in the dayside low-latitude region. The analysis of wave Poynting fluxes, suprathermal electron fluxes and cold electron densities supports the scenario that exohiss leaks from the plasmasphere into the plasmatrough. Quasilinear calculations further reveal that exohiss can potentially cause the resonant scattering loss of radiation belt electrons ~Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062964 Available at: http://doi.wiley.com/10.1002/2014GL062964
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Authors: Kanekal S G, Baker D N, Henderson M G, Li W, Fennell J. F., et al.
Title: Relativistic electron response to the combined magnetospheric impact of a coronal mass ejection overlapping with a high-speed stream: Van Allen Probes observations
Abstract: During early November 2013, the magnetosphere experienced concurrent driving by a coronal mass ejection (CME) during an ongoing high-speed stream (HSS) event. The relativistic electron response to these two kinds of drivers, i.e., HSS and CME, is typically different, with the former often leading to a slower buildup of electrons at larger radial distances, while the latter energizing electrons rapidly with flux enhancements occurring closer to the Earth.We present a detailed analysis of the relativistic electron response including radial profiles of phase space density as observed by both MagEIS and REPT instruments on the Van Allen Probes mission. Data from the MagEIS instrument establishes the behavior of lower energy (<1MeV) electrons which span both intermediary and seed populations du. . .
Date: 09/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021395 Available at: http://doi.wiley.com/10.1002/2015JA021395
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Authors: Li W, Thorne R M, Bortnik J, Baker D N, Reeves G D, et al.
Title: Solar wind conditions leading to efficient radiation belt electron acceleration: A superposed epoch analysis
Abstract: Determining preferential solar wind conditions leading to efficient radiation belt electron acceleration is crucial for predicting radiation belt electron dynamics. Using Van Allen Probes electron observations (>1 MeV) from 2012 to 2015, we identify a number of efficient and inefficient acceleration events separately to perform a superposed epoch analysis of the corresponding solar wind parameters and geomagnetic indices. By directly comparing efficient and inefficient acceleration events, we clearly show that prolonged southward Bz, high solar wind speed, and low dynamic pressure are critical for electron acceleration to >1 MeV energies in the heart of the outer radiation belt. We also evaluate chorus wave evolution using the superposed epoch analysis for the identified efficient and . . .
Date: 09/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL065342 Available at: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015GL065342/abstract
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Authors: Gkioulidou Matina, Ohtani S, Mitchell D G, Ukhorskiy A., Reeves G D, et al.
Title: Spatial structure and temporal evolution of energetic particle injections in the inner magnetosphere during the 14 July 2013 substorm event.
Abstract: Recent results by the Van Allen Probes mission showed that the occurrence of energetic ion injections inside geosynchronous orbit could be very frequent throughout the main phase of a geomagnetic storm. Understanding, therefore, the formation and evolution of energetic particle injections is critical in order to quantify their effect in the inner magnetosphere. We present a case study of a substorm event that occurred during a weak storm (Dst ~ - 40 nT) on 14 July 2013. Van Allen Probe B, inside geosynchronous orbit, observed two energetic proton injections within ten minutes, with different dipolarization signatures and duration. The first one is a dispersionless, short timescale injection pulse accompanied by a sharp dipolarization signature, while the second one is a dispersed, longer t. . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020872 Available at: http://doi.wiley.com/10.1002/2014JA020872
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Authors: Su Zhenpeng, Zhu Hui, Xiao Fuliang, Zong Q.-G., Zhou X.-Z., et al.
Title: Ultra-low-frequency wave-driven diffusion of radiation belt relativistic electrons
Abstract: Van Allen radiation belts are typically two zones of energetic particles encircling the Earth separated by the slot region. How the outer radiation belt electrons are accelerated to relativistic energies remains an unanswered question. Recent studies have presented compelling evidence for the local acceleration by very-low-frequency (VLF) chorus waves. However, there has been a competing theory to the local acceleration, radial diffusion by ultra-low-frequency (ULF) waves, whose importance has not yet been determined definitively. Here we report a unique radiation belt event with intense ULF waves but no detectable VLF chorus waves. Our results demonstrate that the ULF waves moved the inner edge of the outer radiation belt earthward 0.3 Earth radii and enhanced the relativistic electron fl. . .
Date: 12/2015 Publisher: Nature Communications Pages: 10096 DOI: 10.1038/ncomms10096 Available at: http://www.nature.com/doifinder/10.1038/ncomms10096
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Authors: Kilpua E. K. J., Hietala H., Turner D. L., Koskinen H. E. J., Pulkkinen T. I., et al.
Title: Unraveling the drivers of the storm time radiation belt response
Abstract: We present a new framework to study the time evolution and dynamics of the outer Van Allen belt electron fluxes. The framework is entirely based on the large-scale solar wind storm drivers and their substructures. The Van Allen Probe observations, revealing the electron flux behavior throughout the outer belt, are combined with continuous, long-term (over 1.5 solar cycles) geosynchronous orbit data set from GOES and solar wind measurements A superposed epoch analysis, where we normalize the timescales for each substructure (sheath, ejecta, and interface region) allows us to avoid smearing effects and to distinguish the electron flux evolution during various driver structures. We show that the radiation belt response is not random: The electron flux variations are determined by the combined. . .
Date: 04/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL063542 Available at: http://doi.wiley.com/10.1002/2015GL063542
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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
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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
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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: http://doi.wiley.com/10.1002/2014JA020781
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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
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2014
Authors: Reeves G D, Spence H E, Henderson M G, Tu W., Cunningham G. S., et al.
Title: Acceleration and loss driven by VLF chorus: Van Allen Probes observations and DREAM model results
Abstract: For over a decade now we have understood the response of the Earth's radiation belts to solar wind driving are a delicate balance of acceleration and loss processes. Theory has shown that the interaction of relativistic electrons with VLF whistler mode chorus can produce both energization through momentum diffusion and loss through pitch angle diffusion. Recent results from the Van Allen Probes mission has confirmed observationally that chorus can produce both acceleration and loss. The Van Allen Probes satellites are able to measure all the critical particle populations and wave fields with unprecedented precision and resolution but only at the two spacecraft locations. Those spatially-localized observations can be extended globally using three-dimensional diffusion codes such as the DREA. . .
Date: 08/2014 Publisher: IEEE DOI: 10.1109/URSIGASS.2014.6929879 Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6929879
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Authors: Turner D. L., Angelopoulos V, Morley S. K., Henderson M G, Reeves G D, et al.
Title: On the cause and extent of outer radiation belt losses during the 30 September 2012 dropout event
Abstract: On 30 September 2012, a flux “dropout” occurred throughout Earth's outer electron radiation belt during the main phase of a strong geomagnetic storm. Using eight spacecraft from NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Van Allen Probes missions and NOAA's Geostationary Operational Environmental Satellites constellation, we examined the full extent and timescales of the dropout based on particle energy, equatorial pitch angle, radial distance, and species. We calculated phase space densities of relativistic electrons, in adiabatic invariant coordinates, which revealed that loss processes during the dropout were > 90% effective throughout the majority of the outer belt and the plasmapause played a key role in limiting the spatial extent . . .
Date: 03/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 1530 - 1540 DOI: 10.1002/2013JA019446 Available at: http://doi.wiley.com/10.1002/2013JA019446
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Authors: 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: http://doi.wiley.com/10.1002/2014JA019822
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Authors: Turner D. L., Angelopoulos V, Li W, Bortnik J, Ni B, et al.
Title: Competing source and loss mechanisms due to wave-particle interactions in Earth's outer radiation belt during the 30 September to 3 October 2012 geomagnetic storm
Abstract: Drastic variations of Earth's outer radiation belt electrons ultimately result from various competing source, loss, and transport processes, to which wave-particle interactions are critically important. Using 15 spacecraft including NASA's Van Allen Probes, THEMIS, and SAMPEX missions and NOAA's GOES and POES constellations, we investigated the evolution of the outer belt during the strong geomagnetic storm of 30 September to 3 October 2012. This storm's main phase dropout exhibited enhanced losses to the atmosphere at L* < 4, where the phase space density (PSD) of multi-MeV electrons dropped by over an order of magnitude in <4 h. Based on POES observations of precipitating >1 MeV electrons and energetic protons, SAMPEX >1 MeV electrons, and ground observations of band-limited Pc. . .
Date: 03/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 1960 - 1979 DOI: 10.1002/jgra.v119.310.1002/2014JA019770 Available at: http://doi.wiley.com/10.1002/jgra.v119.3http://doi.wiley.com/10.1002/2014JA019770
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Authors: Mozer F S, Agapitov O., Krasnoselskikh V., Lejosne S., Reeves G D, et al.
Title: Direct Observation of Radiation-Belt Electron Acceleration from Electron-Volt Energies to Megavolts by Nonlinear Whistlers
Abstract: The mechanisms for accelerating electrons from thermal to relativistic energies in the terrestrial magnetosphere, on the sun, and in many astrophysical environments have never been verified. We present the first direct observation of two processes that, in a chain, cause this acceleration in Earth’s outer radiation belt. The two processes are parallel acceleration from electron-volt to kilovolt energies by parallel electric fields in time-domain structures (TDS), after which the parallel electron velocity becomes sufficiently large for Doppler-shifted upper band whistler frequencies to be in resonance with the electron gyration frequency, even though the electron energies are kilovolts and not hundreds of kilovolts. The electrons are then accelerated by the whistler perpendicular electri. . .
Date: 07/2014 Publisher: Phys. Rev. Lett. Pages: 035001 DOI: 10.1103/PhysRevLett.113.035001 Available at: http://link.aps.org/doi/10.1103/PhysRevLett.113.035001
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Authors: Usanova M. E., Drozdov A., Orlova K., Mann I. R., Shprits Y., et al.
Title: Effect of EMIC waves on relativistic and ultrarelativistic electron populations: Ground-based and Van Allen Probes observations
Abstract: We study the effect of electromagnetic ion cyclotron (EMIC) waves on the loss and pitch angle scattering of relativistic and ultrarelativistic electrons during the recovery phase of a moderate geomagnetic storm on 11 October 2012. The EMIC wave activity was observed in situ on the Van Allen Probes and conjugately on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity throughout an extended 18 h interval. However, neither enhanced precipitation of >0.7 MeV electrons nor reductions in Van Allen Probe 90° pitch angle ultrarelativistic electron flux were observed. Computed radiation belt electron pitch angle diffusion rates demonstrate that rapid pitch angle diffusion is confined to low pitch angles and cannot reach 90°. For the first time, from both obse. . .
Date: 03/2014 Publisher: Geophysical Research Letters Pages: 1375 - 1381 DOI: 10.1002/2013GL059024 Available at: http://doi.wiley.com/10.1002/2013GL059024
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