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2018
Authors: Yu Xiongdong, Yuan Zhigang, Li Haimeng, Huang Shiyong, Wang Dedong, et al.
Title: Response of banded whistler-mode waves to the enhancement of solar wind dynamic pressure in the inner Earth's magnetosphere
Abstract: With observations of Van Allen Probe A, in this letter we display a typical event where banded whistler waves shifted up their frequencies with frequency bands broadening as a response to the enhancement of solar wind dynamic pressure. Meanwhile, the anisotropy of electrons with energies about several tens of keV was observed to increase. Through the comparison of the calculated wave growth rates and observed wave spectral intensity, we suggest that those banded whistler waves observed with frequencies shifted up and frequency bands broadening could be locally excited by these hot electrons with increased anisotropy. The current study provides a great in situ evidence for the influence on frequencies of banded whistler waves by the enhancement of solar wind dynamic pressures, which reveals. . .
Date: Mar-08-2020 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078849 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078849
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Authors: Hartley D. P., Kletzing C A, De Pascuale S., Kurth W S, and ík O.
Title: Determining Plasmaspheric Densities from Observations of Plasmaspheric Hiss
Abstract: A new method of inferring electron plasma densities inside of the plasmasphere is presented. Utilizing observations of the electric and magnetic field wave power associated with plasmaspheric hiss, coupled with the cold plasma dispersion relation, permits calculation of the plasma density. This methodology yields a density estimate for each frequency channel and time interval where plasmaspheric hiss is observed and is shown to yield results that are generally in agreement with densities determined via other methods. A statistical calibration is performed against the density from the upper hybrid line, accounting for both systematic offsets and distribution scatter in the hiss‐inferred densities. This calculation and calibration methodology provides accurate density estimates, both stati. . .
Date: 08/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025658 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025658
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Authors: Nishi Katsuki, Shiokawa Kazuo, and Spence Harlan
Title: Magnetospheric source region of auroral finger-like structures observed by the RBSP-A satellite
Abstract: Auroral finger‐like structures appear equatorward of the auroral oval in the diffuse auroral region and contribute to the auroral fragmentation into patches. A previous report of the first conjugate observation of auroral finger‐like structures using a THEMIS GBO camera and the THEMIS‐E satellite at a radial distance of ∼8 RE showed anti‐phase oscillations of magnetic and plasma pressures in the dawnside plasma sheet. In the present study, we report another simultaneous observation of auroral finger‐like structures at Gillam, Canada at ∼0900 UT (0230 magnetic local time) on November 14, 2014 with the RBSP satellites at 5.8 RE in the inner magnetosphere. From this simultaneous observation event, we obtained the following observations. (1) Auroral finger‐like structures devel. . .
Date: 08/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025480 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025480
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Authors: Li Li, Zhou Xu-Zhi, Omura Yoshiharu, Wang Zi-Han, Zong Qiu-Gang, et al.
Title: Nonlinear drift resonance between charged particles and ultra-low frequency waves: Theory and Observations
Abstract: In Earth's inner magnetosphere, electromagnetic waves in the ultra‐low frequency (ULF) range play an important role in accelerating and diffusing charged particles via drift resonance. In conventional drift‐resonance theory, linearization is applied under the assumption of weak wave‐particle energy exchange so particle trajectories are unperturbed. For ULF waves with larger amplitudes and/or durations, however, the conventional theory becomes inaccurate since particle trajectories are strongly perturbed. Here, we extend the drift‐resonance theory into a nonlinear regime, to formulate nonlinear trapping of particles in a wave‐carried potential well, and predict the corresponding observable signatures such as rolled‐up structures in particle energy spectrum. After considering how. . .
Date: 08/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL079038 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079038
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Authors: Xiang Zheng, Tu Weichao, Ni Binbin, Henderson M G, and Cao Xing
Title: A Statistical Survey of Radiation Belt Dropouts Observed by Van Allen Probes
Abstract: N/A
Date: 08/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078907 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078907
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Authors: Noh Sung-Jun, Lee Dae-Young, Choi Cheong-Rim, Kim Hyomin, and Skoug Ruth
Title: Test of Ion Cyclotron Resonance Instability Using Proton Distributions Obtained From Van Allen Probe-A Observations
Abstract: Anisotropic velocity distributions of protons have long been considered as free energy sources for exciting electromagnetic ion cyclotron (EMIC) waves in the Earth's magnetosphere. Here we rigorously calculated the proton anisotropy parameter using proton data obtained from Van Allen Probe‐A observations. The calculations are performed for times during EMIC wave events (distinguishing the times immediately after and before EMIC wave onsets) and for times exhibiting no EMIC waves. We find that the anisotropy values are often larger immediately after EMIC wave onsets than the times just before EMIC wave onsets and the non‐EMIC wave times. The increase in anisotropy immediately after the EMIC wave onsets is rather small but discernible, such that the average increase is by ~15% relative t. . .
Date: 08/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025385 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025385
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Authors: Yue Chao, Bortnik Jacob, Li Wen, Ma Qianli, Gkioulidou Matina, et al.
Title: The composition of plasma inside geostationary orbit based on Van Allen Probes observations
Abstract: The composition of the inner magnetosphere is of great importance for determining the plasma pressure, and thus the currents and magnetic field configuration. In this study, we perform a statistical survey of equatorial plasma pressure distributions and investigate the relative contributions of ions and electron with different energies inside of geostationary orbit under two AE levels based on over sixty months of observations from the HOPE and RBSPICE mass spectrometers on board Van Allen Probes. We find that the total and partial pressures of different species increase significantly at high AE levels with Hydrogen (H+) pressure being dominant in the plasmasphere. The pressures of the heavy ions and electrons increase outside the plasmapause and develop a strong dawn‐dusk asymmetry with. . .
Date: 07/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025344 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025344
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Authors: Boardsen Scott A., Hospodarsky George B., Min Kyungguk, Averkamp Terrance F., Bounds Scott R., et al.
Title: Determining the wave vector direction of equatorial fast magnetosonic waves
Abstract: We perform polarization analysis of the equatorial fast magnetosonic waves electric field over a 20 minute interval of Van Allen Probes A Waveform Receiver burst mode data. The wave power peaks at harmonics of the proton cyclotron frequency indicating the spacecraft is near or in the source region. The wave vector is inferred from the direction of the major axis of the electric field polarization ellipsoid and the sign of the phase between the longitudinal electric and compressional magnetic field components. We show that wave vector is preferentially in the azimuthal direction as opposed to the radial direction. From Poynting flux analysis one would infer that the wave vector is primarily in the radial direction. We show that the error in the Poynting flux is large ~ 90°. These results s. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078695 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078695
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Authors: Engebretson M. J., Posch J. L., Braun D. J., Li W, Ma Q, et al.
Title: EMIC wave events during the four GEM QARBM challenge intervals
Abstract: This paper presents observations of EMIC waves from multiple data sources during the four GEM challenge events in 2013 selected by the GEM “Quantitative Assessment of Radiation Belt Modeling” focus group: March 17‐18 (Stormtime Enhancement), May 31‐June 2 (Stormtime Dropout), September 19‐20 (Non‐storm Enhancement), and September 23‐25 (Non‐storm Dropout). Observations include EMIC wave data from the Van Allen Probes, GOES, and THEMIS spacecraft in the near‐equatorial magnetosphere and from several arrays of ground‐based search coil magnetometers worldwide, as well as localized ring current proton precipitation data from low‐altitude POES spacecraft. Each of these data sets provides only limited spatial coverage, but their combination shows consistent occurrence patte. . .
Date: 07/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025505 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025505
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Authors: Shumko Mykhaylo, Turner Drew L, O'Brien T P, Claudepierre Seth G., Sample John, et al.
Title: Evidence of Microbursts Observed Near the Equatorial Plane in the Outer Van Allen Radiation Belt
Abstract: We present the first evidence of electron microbursts observed near the equatorial plane in Earth's outer radiation belt. We observed the microbursts on March 31st, 2017 with the Magnetic Electron Ion Spectrometer and RBSP Ion Composition Experiment on the Van Allen Probes. Microburst electrons with kinetic energies of 29‐92 keV were scattered over a substantial range of pitch angles, and over time intervals of 150‐500 ms. Furthermore, the microbursts arrived without dispersion in energy, indicating that they were recently scattered near the spacecraft. We have applied the relativistic theory of wave‐particle resonant diffusion to the calculated phase space density, revealing that the observed transport of microburst electrons is not consistent with the hypothesized quasi‐linear ap. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078451 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078451
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Authors: Takahashi Kazue, Denton Richard E, Motoba Tetsuo, Matsuoka Ayako, Kasaba Yasumasa, et al.
Title: Impulsively Excited Nightside Ultralow Frequency Waves Simultaneously Observed On and Off the Magnetic Equator
Abstract: The Arase spacecraft is capable of observing ultralow‐frequency waves in the inner magnetosphere at intermediate magnetic latitudes, a region sparsely covered by previous space craft missions. We report a series of impulsively excited fundamental toroidal mode standing Alfvén waves in the midnight sector observed by Arase outside the plasmasphere at magnetic latitudes 13–24° . The wave onsets are concurrent with Pi2 onsets detected by the Van Allen Probe B spacecraft at the magnetic equator in the duskside plasmasphere and by ground magnetometers at low latitudes. The duration of each toroidal wave packet is ∼20 min, which is much longer than that of the corresponding Pi2 wave packet. The toroidal waves cannot be the source of high‐latitude Pi2 waves because they were not detecte. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078731 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078731
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Authors: áhlava J., ěmec F., ík O., šová I., Hospodarskyy G. B., et al.
Title: Longitudinal dependence of whistler mode electromagnetic waves in the Earth's inner magnetosphere
Abstract: We use the measurements performed by the DEMETER (2004‐2010) and the Van Allen Probes (2012‐2016, still operating) spacecraft to investigate the longitudinal dependence of the intensity of whistler mode waves in the Earth's inner magnetosphere. We show that a significant longitudinal dependence is observed inside the plasmasphere on the nightside, primarily in the frequency range 400 Hz–2 kHz. On the other hand, almost no longitudinal dependence is observed on the dayside. The obtained results are compared to the lightning occurrence rate provided by the OTD/LIS mission normalized by a factor accounting for the ionospheric attenuation. The agreement between the two dependencies indicates that lightning generated electromagnetic waves may be responsible for the observed effect, thus s. . .
Date: 07/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025284 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025284
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Authors: Liu Nigang, Su Zhenpeng, Zheng Huinan, Wang Yuming, and Wang Shui
Title: Magnetosonic harmonic falling and rising frequency emissions potentially generated by nonlinear wave-wave interactions in the Van Allen radiation belts
Abstract: Magnetosonic waves play a potentially important role in the complex evolution of the radiation belt electrons. These waves typically appear as discrete emission lines along the proton gyrofrequency harmonics, consistent with the prediction of the local Bernstein mode instability of hot proton ring distributions. Magnetosonic waves are nearly dispersionless particularly at low harmonics and therefore have the roughly unchanged frequency‐time structures during the propagation. On the basis of Van Allen Probes observations, we here present the first report of magnetosonic harmonic falling and rising frequency emissions. They lasted for up to 2 h and occurred primarily in the dayside plasmatrough following intense substorms. These harmonic emission lines were well spaced by the proton gyrofr. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL079232 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079232
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Authors: Zhang Dianjun, Liu Wenlong, Li Xinlin, Sarris Theodore, Xiao Chao, et al.
Title: Observations of impulsive electric fields induced by Interplanetary Shock
Abstract: We investigate the characteristics of impulsive electric fields in Earth's magnetosphere, as measured by the Van Allen Probes, in association with interplanetary shocks, as measured by ACE and Wind spacecraft in the solar wind from January 2013 to July 2016. It is shown that electric field impulses are mainly induced by global compressions by the shocks, mostly in the azimuthal direction and the amplitudes of the initial electric field impulses are positively correlated with the rate of increase of dynamic pressure across the shock in the dayside. It is also shown that the temporal profile of the impulse is related to the temporal profile of the solar wind dynamic pressure, Pd. It is suggested that during the first period of the impulse the evolution of the electric field is directly contr. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078809 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078809
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Authors: Capannolo L., Li W, Ma Q, Zhang X.-J., Redmon R. J., et al.
Title: Understanding the Driver of Energetic Electron Precipitation Using Coordinated Multisatellite Measurements
Abstract: Magnetospheric plasma waves play a significant role in ring current and radiation belt dynamics, leading to pitch angle scattering loss and/or stochastic acceleration of the particles. During a non‐storm time dropout event on 24 September 2013, intense electromagnetic ion cyclotron (EMIC) waves were detected by Van Allen Probe A (Radiation Belt Storm Probes‐A). We quantitatively analyze a conjunction event when Van Allen Probe A was located approximately along the same magnetic field line as MetOp‐01, which detected simultaneous precipitation of >30 keV protons and energetic electrons over an unexpectedly broad energy range (>~30 keV). Multipoint observations together with quasi‐linear theory provide direct evidence that the observed electron precipitation at higher energy (>~700 k. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078604 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078604
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Authors: Zhao H., Baker D N, Li X, Jaynes A. N., and Kanekal S G
Title: The Acceleration of Ultrarelativistic Electrons During a Small to Moderate Storm of 21 April 2017
Abstract: The ultrarelativistic electrons (E > ~3 MeV) in the outer radiation belt received limited attention in the past due to sparse measurements. Nowadays, the Van Allen Probes measurements of ultrarelativistic electrons with high energy resolution provide an unprecedented opportunity to study the dynamics of this population. In this study, using data from the Van Allen Probes, we report significant flux enhancements of ultrarelativistic electrons with energies up to 7.7 MeV during a small to moderate geomagnetic storm. The underlying physical mechanisms are investigated by analyzing and simulating the evolution of electron phase space density. The results suggest that during this storm, the acceleration mechanism for ultrarelativistic electrons in the outer belt is energy‐dependent: local acc. . .
Date: 06/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078582 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078582
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Authors: Ren Jie, Zong Qiu-Gang, Miyoshi Yoshizumi, Rankin Robert, Spence Harlan E, et al.
Title: A comparative study of ULF waves' role in the dynamics of charged particles in the plasmasphere: Van Allen Probes observation
Abstract: By analyzing observations from Van Allen Probes in its inbound and outbound orbits, we present evidence of coherent enhancement of cold plasmaspheric electrons and ions due to drift‐bounce resonance with ULF waves. From 18:00 UT on 28 May 2017 to 10:00 UT on 29 May 2017, newly formed poloidal mode standing ULF waves with significant electric field oscillations were observed in two consecutive orbits when Probe B was travelling inbound. In contrast to observations during outbound orbits, the cold (< 150 eV) electorns measured by the HOPE instrument were characterized by flux enhancements several times larger and bi‐directional pitch angle distributions during inbound orbits. The electron number density inferred from upper hybrid waves is twice as larger as during inbound orbits, which w. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025255 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025255
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Authors: Damiano P.A., Chaston C.C., Hull A.J., and Johnson J.R.
Title: Electron Distributions in Kinetic Scale Field Line Resonances: A Comparison of Simulations and Observations
Abstract: Observations in kinetic scale field line resonances, or eigenmodes of the geomagnetic field, reveal highly field‐aligned plateaued electron distributions. By combining observations from the Van Allen Probes and Cluster spacecraft with a hybrid kinetic gyrofluid simulation we show how these distributions arise from the nonlocal self‐consistent interaction of electrons with the wavefield. This interaction is manifested as electron trapping in the standing wave potential. The process operates along most of the field line and qualitatively accounts for electron observations near the equatorial plane and at higher latitudes. In conjunction with the highly field‐aligned plateaus, loss cone features are also evident, which result from the action of the upward‐directed wave parallel electr. . .
Date: 06/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL077748 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL077748
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Authors: Zhang X.-J., Mourenas D., Artemyev A. V., Angelopoulos V, and Thorne R M
Title: Electron flux enhancements at L  = 4.2 observed by Global Positioning System satellites: Relationship with solar wind and geomagnetic activity
Abstract: Determining solar wind and geomagnetic activity parameters most favorable to strong electron flux enhancements is an important step towards forecasting radiation belt dynamics. Using electron flux measurements from Global Positioning System satellites at L = 4.2 in 2009‐2016, we seek statistical relationships between flux enhancements at different energies and solar wind dynamic pressure Pdyn, AE, and Kp, from hundreds of events inside and outside the plasmasphere. Most ⩾1 MeV electron flux enhancements occur during non‐storm (or weak storm) times. Flux enhancements of 4 MeV electrons outside the plasmasphere occur during periods of low Pdyn and high AE. We perform superposed epoch analyses of GPS electron fluxes, along with solar wind and geomagnetic indices, 40 keV electron flu. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025497 Available at: http://doi.wiley.com/10.1029/2018JA025497http://onlinelibrary.wiley.com/wol1/doi/10.1029/2018JA025497/fullpdfhttps://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1029%2F2018JA025497
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Authors: Shi R., Mourenas D., Artemyev A., Li W, and Ma Q
Title: Highly Oblique Lower-Band Chorus Statistics: Dependencies of Wave Power on Refractive Index and Geomagnetic Activity
Abstract: We use 3 years of Van Allen Probes observations of highly oblique lower‐band chorus waves at low latitudes over L = 4–6 to provide a comprehensive statistics of the distribution of their magnetic and electric powers and full energy density as a function of wave refractive index N, L shell, and geomagnetic activity AE. We use the refractive index calculated either in the cold plasma approximation or in the quasi‐electrostatic (hot plasma) approximation and either observed wave electric fields or corrected wave electric fields accounting for the formation of a plasma sheath around antenna probes in a low‐density plasma. Approximate fits to the maximum refractive index and to the magnetic wave power profile of highly oblique waves are provided as a function of AE and L. Such fits shou. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025337 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025337
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Authors: Remya B., Sibeck D G, Halford A J, Murphy K. R., Reeves G D, et al.
Title: Ion Injection Triggered EMIC Waves in the Earth's Magnetosphere
Abstract: We present Van Allen Probe observations of electromagnetic ion cyclotron (EMIC) waves triggered solely due to individual substorm‐injected ions in the absence of storms or compressions of the magnetosphere during 9 August 2015. The time at which the injected ions are observed directly corresponds to the onset of EMIC waves at the location of Van Allen Probe A (L = 5.5 and 18:06 magnetic local time). The injection was also seen at geosynchronous orbit by the Geostationary Operational Environmental Satellite and Los Alamos National Laboratory spacecraft, and the westward(eastward) drift of ions(electrons) was monitored by Los Alamos National Laboratory spacecraft at different local times. The azimuthal location of the injection was determined by tracing the injection signatures backward in. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025354 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025354
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Authors: Ukhorskiy A Y, Sorathia K. A., Merkin V. G., Sitnov M I, Mitchell D G, et al.
Title: Ion Trapping and Acceleration at Dipolarization Fronts: High-Resolution MHD/Test-Particle Simulations
Abstract: Much of plasma heating and transport from the magnetotail into the inner magnetosphere occurs in the form of mesoscale discrete injections associated with sharp dipolarizations of magnetic field (dipolarization fronts). In this paper we investigate the role of magnetic trapping in acceleration and transport of the plasmasheet ions into the ring current. For this purpose we use high‐resolution global MHD and three‐dimensional test‐particle simulations. It is shown that trapping, produced by sharp magnetic field gradients at the interface between dipolarizations and the ambient plasma, affect plasmasheet protons with energies above approximately 10 keV, enabling their transport across more than 10 Earth radii and acceleration by a factor of 10. Our estimates show that trapping is impor. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025370 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025370
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Authors: Sorathia K. A., Ukhorskiy A Y, Merkin V. G., Fennell J. F., and Claudepierre S G
Title: Modeling the Depletion and Recovery of the Outer Radiation Belt During a Geomagnetic Storm: Combined MHD and Test Particle Simulations
Abstract: During geomagnetic storms the intensities of the outer radiation belt electron population can exhibit dramatic variability. Deep depletions in intensity during the main phase are followed by increases during the recovery phase, often to levels that significantly exceed their pre‐storm values. To study these processes, we simulate the evolution of the outer radiation belt during the 17 March 2013 geomagnetic storm using our newly‐developed radiation belt model (CHIMP) based on test particle and coupled 3D ring current and global MHD simulations, and driven solely with solar wind and F10.7 flux data. Our approach differs from previous work in that we use MHD information to identify regions of strong, bursty, and azimuthally localized Earthward convection in the magnetotail where test. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025506 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025506
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Authors: Teng S., Zhao J., Tao X., Wang S., and Reeves G D
Title: Observation of Oblique Lower Band Chorus Generated by Nonlinear Three-Wave Interaction
Abstract: Oblique whistler mode waves have been suggested to play an important role in radiation belt electron dynamics. Recently, Fu et al. [2017] proposed that highly oblique lower band whistler waves could be generated by nonlinear three‐wave resonance. Here we present the first observational evidence of such process, using Van Allen Probes data, where an oblique lower band chorus wave is generated by two quasi‐parallel waves through nonlinear three‐wave interaction. The wave resonance condition is satisfied even in the presence of frequency chirping of one of the pump waves. Different from the simulation results of Fu et al. [2017], simultaneous particle data do not show a plateau in the electron distribution, which could be due to the very weak intensity of the generated waves. These resu. . .
Date: 06/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078765 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078765
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Authors: Zhang Zhenxia, Chen Lunjin, Li Xinqiao, Xia Zhiyang, Heelis Roderick A., et al.
Title: Observed propagation route of VLF transmitter signals in the magnetosphere
Abstract: Signals of powerful ground transmitters at various places have been detected by satellites in near‐Earth space. The study on propagation mode, ducted or nonducted, has attracted much attentions for several decades. Based on the statistical results from Van Allen Probes (data from Oct. 2012 to Mar. 2017) and DEMETER satellite (from Jan. 2006 to Dec. 2007), we present the ground transmitter signals distributed clearly in ionosphere and magnetosphere. The observed propagation route in the meridian plane in the magnetosphere for each of various transmitters from the combination of DEMETER and Van Allen Probes data in night time is revealed for the first time. We use realistic ray tracing simulation and compare simulation results against Van Allen Probes and DEMETER observation. By comparison. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025637 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025637
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Authors: Artemyev A. V., Zhang X.-J., Angelopoulos V, Runov A., Spence H E, et al.
Title: Plasma anisotropies and currents in the near-Earth plasma sheet and inner magnetosphere
Abstract: The region occupying radial distances of ∼3 − 9 Earth radii (RE) in the night side, includes the near‐Earth plasma sheet with stretched magnetic field lines and the inner magnetosphere with strong dipolar magnetic field. In this region, the plasma flow energy, which was injected into the inner magnetosphere from the magnetotail, is converted to particle heating and electromagnetic wave generation. These important processes are controlled by plasma anisotropies, which are the focus of this study. Using measurements of THEMIS and Van Allen Probes in this transition region we obtain radial profiles of ion and electron temperatures and anisotropies for various geomagnetic activity levels. Ion and electron anisotropies vary with the geomagnetic activity in opposite directions. Paralle. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025232 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025232
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Authors: Zhang X.-J., Thorne R., Artemyev A., Mourenas D., Angelopoulos V, et al.
Title: Properties of intense field-aligned lower-band chorus waves: Implications for nonlinear wave-particle interactions
Abstract: Resonant interactions between electrons and chorus waves are responsible for a wide range of phenomena in near‐Earth space (e.g., diffuse aurora, acceleration of MeV electrons, etc.). Although quasi‐linear diffusion is believed to be the primary paradigm for describing such interactions, an increasing number of investigations suggest that nonlinear effects are also important in controlling the rapid dynamics of electrons. However, present models of nonlinear wave‐particle interactions, which have been successfully used to describe individual short‐term events, are not directly applicable for a statistical evaluation of nonlinear effects and the long‐term dynamics of the outer radiation belt, because they lack information on the properties of intense (nonlinearly resonating with e. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025390 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025390
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Authors: Tang C. L., Xie X. J., Ni B, Su Z. P., Reeves G D, et al.
Title: Rapid Enhancements of the Seed Populations in the Heart of the Earth's Outer Radiation Belt: A Multicase Study
Abstract: To better understand rapid enhancements of the seed populations (hundreds of keV electrons) in the heart of the Earth's outer radiation belt (L* ~ 3.5–5.0) during different geomagnetic activities, we investigate three enhancement events measured by Van Allen Probes in detail. Observations of the fluxes and the pitch angle distributions of energetic electrons are analyzed to determine rapid enhancements of the seed populations. Our study shows that three specified processes associated with substorm electron injections can lead to rapid enhancements of the seed populations, and the electron energy increases up to 342 keV. In the first process, substorm electron injections accompanied by the transient and intense substorm electric fields can directly lead to rapid enhancements of the seed p. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2017JA025142 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2017JA025142
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Authors: Motoba T., Ohtani S, Gkioulidou M., Ukhorskiy A., Mitchell D G, et al.
Title: Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit
Abstract: This paper examines how hydrogen, helium and oxygen (H, He and O) ion fluxes at 1–1000 keV typically respond to local magnetic dipolarization inside geosynchronous orbit (GEO). We extracted 144 dipolarizations which occurred at magnetic inclination > 30° from the 2012–2016 tail seasons' observations of the Van Allen Probes spacecraft and then defined typical flux changes of these ion species by performing a superposed epoch analysis. On average, the dipolarization inside GEO is accompanied by a precursory transient decrease in the northward magnetic field component, transient impulsive enhancement in the westward electric field component, and decrease (increase) in the proton density (temperature). The coincident ion species experience an energy‐dependent flux change, consisting of . . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025557 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025557
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Authors: Ohtani S, Motoba T., Gkioulidou M., Takahashi K., and Singer H J
Title: Spatial Development of the Dipolarization Region in the Inner Magnetosphere
Abstract: The present study examines dipolarization events observed by the Van Allen Probes within 5.8 RE from Earth. It is found that the probability of occurrence is significantly higher in the dusk‐to‐midnight sector than in the midnight‐to‐dawn sector, and it deceases sharply earthward. A comparison with observations made at nearby satellites shows that dipolarization signatures are often highly correlated (c.c. > 0.8) within 1 hr in MLT and 1 RE in RXY, and the dipolarization region expands earthward and westward in the dusk‐to‐midnight sector. The westward expansion velocity is estimated at 0.4 hr (in MLT) per minute, or 60 km/s, which is consistent with the previously reported result for geosynchronous dipolarization. The earthward expansion is apparently less systematic than the . . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025443 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025443
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Authors: Qin Murong, Hudson Mary, Millan Mary, Woodger Leslie, and Shekhar Sapna
Title: Statistical investigation of the efficiency of EMIC waves in precipitating relativistic electrons
Abstract: Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause Relativistic Electron Precipitation (REP). In our study, we carry out 4 years of analysis from 2013 to 2016, with relativistic electron precipitation spikes obtained from POES satellites and EMIC waves observation from Van Allen Probes. Among the 473 coincidence events when POES satellites go through the region conjugate to EMIC wave activity, only 127 are associated with REP. Additionally, the coincidence occurrence rate is about 10% higher than the random coincidence occurrence rate, indicating that EMIC waves and relativistic electrons can be statistically related, but the link is weaker than expected. H+ band EMIC waves have been regarded as less important than He+ band EMIC waves for the precipitation of relativist. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025419 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025419
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Authors: Murphy Kyle R., Inglis Andrew R., Sibeck David G., Rae Jonathan, Watt Clare E. J., et al.
Title: Determining the mode, frequency, and azimuthal wave number of ULF waves during a HSS and moderate geomagnetic storm
Abstract: Ultra‐low frequency (ULF) waves play a fundamental role in the dynamics of the inner‐magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion and discrete ULF wave power can energize electrons through a resonant interaction. Using observations from the Magnetospheric Multiscale (MMS) mission, we characterize the evolution of ULF waves during a high‐speed solar wind stream (HSS) and moderate geomagnetic storm while there is an enhancement of the outer radiation belt. The Automated Flare Inference of Oscillations (AFINO) code is used to distinguish discrete ULF wave power from broadband wave power during the HSS. During periods of discrete wave power and utilizing the close separation of the MMS sp. . .
Date: 05/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2017JA024877 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2017JA024877
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Authors: Mourenas D., Zhang X.-J., Artemyev A. V., Angelopoulos V, Thorne R M, et al.
Title: Electron nonlinear resonant interaction with short and intense parallel chorus wave-packets
Abstract: One of the major drivers of radiation belt dynamics, electron resonant interaction with whistler‐mode chorus waves, is traditionally described using the quasi‐linear diffusion approximation. Such a description satisfactorily explains many observed phenomena, but its applicability can be justified only for sufficiently low intensity, long duration waves. Recent spacecraft observations of a large number of very intense lower band chorus waves (with magnetic field amplitudes sometimes reaching ∼1% of the background) therefore challenge this traditional description, and call for an alternative approach when addressing the global, long‐term effects of the nonlinear interaction of these waves with radiation belt electrons. In this paper, we first use observations from the Van Allen Probe. . .
Date: 05/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025417 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025417
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Authors: Zhang Wenxun, Fu Song, Gu Xudong, Ni Binbin, Xiang Zheng, et al.
Title: Electron Scattering by Plasmaspheric Hiss in a Nightside Plume
Abstract: Plasmaspheric hiss is known to play an important role in radiation belt electron dynamics in high plasma density regions. We present observations of two crossings of a plasmaspheric plume by the Van Allen Probes on 26 December 2012, which occurred unusually at the post‐midnight‐to‐dawn sector between L ~ 4–6 during a geomagnetically quiet period. This plume exhibited pronounced electron densities higher than those of the average plume level. Moderate hiss emissions accompanied the two plume crossings with the peak power at about 100 Hz. Quantification of quasi‐linear bounce‐averaged electron scattering rates by hiss in the plume demonstrates that the waves are efficient to pitch angle scatter ~10–100 keV electrons at rates up to ~10−4 s−1 near the loss cone but become gra. . .
Date: 05/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL077212 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL077212
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Authors: ěmec F., ík O., Boardsen S. A., Hospodarsky G B, and Kurth W S
Title: Equatorial noise with quasiperiodic modulation: Multipoint observations by the Van Allen Probes spacecraft
Abstract: Electromagnetic wave measurements performed by the two Van Allen Probes spacecraft are used to analyze equatorial noise emissions with a quasiperiodic modulation of the wave intensity. These waves are confined to the vicinity of the geomagnetic equator, and they occur primarily on the dayside. In situ plasma number density measurements are used to evaluate density variations related to the wave occurrence. It is shown that the events are sometimes effectively confined to low density regions, being observed at successive satellite passes over a time duration as long as one hour. The events typically occur outside the plasmasphere, and they are often cease to exist just at the plasmapause. The analysis of the spatial separations of the spacecraft at the times when the events were observed si. . .
Date: 05/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025482 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025482
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Authors: Meredith Nigel P, Horne Richard B, Kersten Tobias, Li Wen, Bortnik Jacob, et al.
Title: Global model of plasmaspheric hiss from multiple satellite observations
Abstract: We present a global model of plasmaspheric hiss, using data from eight satellites, extending the coverage and improving the statistics of existing models. We use geomagnetic activity dependent templates to separate plasmaspheric hiss from chorus. In the region 22‐14 MLT the boundary between plasmaspheric hiss and chorus moves to lower L∗ values with increasing geomagnetic activity. The average wave intensity of plasmaspheric hiss is largest on the dayside and increases with increasing geomagnetic activity from midnight through dawn to dusk. Plasmaspheric hiss is most intense and spatially extended in the 200‐500 Hz frequency band during active conditions, 400 Date: 05/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025226 Available at: http://doi.wiley.com/10.1029/2018JA025226http://onlinelibrary.wiley.com/wol1/doi/10.1029/2018JA025226/fullpdfhttps://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1029%2F2018JA025226
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Authors: Wang C., Rankin R, Wang Y., Zong Q.-G., Zhou X., et al.
Title: Poloidal mode wave-particle interactions inferred from Van Allen Probes and CARISMA ground-based observations
Abstract: Ultra‐low‐frequency (ULF) wave and test particle models are used to investigate the pitch angle and energy dependence of ion differential fluxes measured by the Van Allen Probes spacecraft on October 6th, 2012. Analysis of the satellite data reveals modulations in differential flux resulting from drift resonance between H+ ions and fundamental mode poloidal Alfvén waves detected near the magnetic equator at L∼5.7. Results obtained from simulations reproduce important features of the observations, including a substantial enhancement of the differential flux between ∼20° − 40° pitch angle for ion energies between ∼90 − 220keV, and an absence of flux modulations at 90°. The numerical results confirm predictions of drift‐bounce resonance theory and show good quantit. . .
Date: 05/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2017JA025123 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2017JA025123
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Authors: Mitani K., Seki K., Keika K, Gkioulidou M., Lanzerotti L J, et al.
Title: Radial Transport of Higher-Energy Oxygen Ions Into the Deep Inner Magnetosphere Observed by Van Allen Probes
Abstract: The transport mechanism of the ring current ions differs among ion energies. Lower‐energy (≲150 keV) ions are well known to be transported convectively. Higher‐energy (≳150 keV) protons are reported to be transported diffusively, while there are few reports about transport of higher‐energy oxygen ions. We report the radial transport of higher‐energy oxygen ions into the deep inner magnetosphere during the late main phase of the magnetic storm on 23–25 April 2013 observed by the Van Allen Probes spacecraft. An enhancement of 1–100 mHz magnetic fluctuations is simultaneously observed. Observations of 3 and 30 mHz geomagnetic pulsations indicate the azimuthal mode number is ≤10. The fluctuations can resonate with the drift and bounce motions of the oxygen ions. The results s. . .
Date: 05/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL077500 Available at: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL077500
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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
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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
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Authors: Zhao H., Friedel R H W, Chen Y., Reeves G D, Baker D N, et al.
Title: An empirical model of radiation belt electron pitch angle distributions based on Van Allen Probes measurements
Abstract: Based on over 4 years of Van Allen Probes measurements, an empirical model of radiation belt electron equatorial pitch angle distribution (PAD) is constructed. The model, developed by fitting electron PADs with Legendre polynomials, provides the statistical PADs as a function of L‐shell (L=1 – 6), magnetic local time (MLT), electron energy (~30 keV – 5.2 MeV), and geomagnetic activity (represented by the Dst index), and is also the first empirical PAD model in the inner belt and slot region. For MeV electrons, model results show more significant day‐night PAD asymmetry of electrons with higher energies and during disturbed times, which is caused by geomagnetic field configuration and flux radial gradient changes. Steeper PADs with higher fluxes around 90° pitch angle (PA) and lowe. . .
Date: 04/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025277 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025277
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Authors: Lejosne ène, Kunduri B. S. R., Mozer F S, and Turner D. L.
Title: Energetic electron injections deep into the inner magnetosphere: a result of the subauroral polarization stream (SAPS) potential drop
Abstract: It has been reported that the dynamics of energetic (tens to hundreds of keV) electrons and ions is inconsistent with the theoretical picture in which the large‐scale electric field is a superposition of corotation and convection electric fields. Combining one year of measurements by the Super Dual Auroral Radar Network, DMSP F‐18 and the Van Allen Probes, we show that subauroral polarization streams are observed when energetic electrons have penetrated below L = 4. Outside the plasmasphere in the premidnight region, potential energy is subtracted from the total energy of ions and added to the total energy of electrons during SAPS onset. This potential energy is converted into radial motion as the energetic particles drift around Earth and leave the SAPS azimuthal sector. As a result, . . .
Date: 04/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL077969 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL077969
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Authors: Kubota Yuko, Omura Yoshiharu, Kletzing Craig, and Reeves Geoff
Title: Generation process of large-amplitude upper band chorus emissions observed by Van Allen Probes
Abstract: We analyze large‐amplitude upper‐band chorus emissions measured near the magnetic equator by the EMFISIS (Electric and Magnetic Field Instrument Suite and Integrated Science) instrument package onboard the Van Allen Probes. In setting up the parameters of source electrons exciting the emissions based on theoretical analyses and observational results measured by the HOPE (Helium Oxygen Proton Electron) instrument, we calculate threshold and optimum amplitudes with the nonlinear wave growth theory. We find that the optimum amplitude is larger than the threshold amplitude obtained in the frequency range of the chorus emissions and that the wave amplitudes grow between the threshold and optimum amplitudes. In the frame of the wave growth process, the nonlinear growth rates are much greater. . .
Date: 04/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2017JA024782 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2017JA024782
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Authors: Murphy Kyle R., Watt C. E. J., Mann Ian R., Rae Jonathan, Sibeck David G., et al.
Title: The global statistical response of the outer radiation belt during geomagnetic storms
Abstract: Using the total radiation belt electron content calculated from Van Allen Probe phase space density (PSD), the time‐dependent and global response of the outer radiation belt during storms is statistically studied. Using PSD reduces the impacts of adiabatic changes in the main phase, allowing a separation of adiabatic and non‐adiabatic effects, and revealing a clear modality and repeatable sequence of events in storm‐time radiation belt electron dynamics. This sequence exhibits an important first adiabatic invariant (μ) dependent behaviour in the seed (150 MeV/G), relativistic (1000 MeV/G), and ultra‐relativistic (4000 MeV/G) populations. The outer radiation belt statistically shows an initial phase dominated by loss followed by a second phase of rapid acceleration, whilst the seed. . .
Date: 04/2018 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL076674 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2017GL076674
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Authors: Lejosne ène, and Mozer F S
Title: Magnetic activity dependence of the electric drift below L=3
Abstract: More than two years of magnetic and electric field measurements by the Van Allen Probes are analyzed with the objective of determining the average effects of magnetic activity on the electric drift below L=3. The study finds that an increase in magnetospheric convection leads to a decrease in the magnitude of the azimuthal component of the electric drift, especially in the night‐side. The amplitude of the slowdown is a function of L, local time MLT, and Kp, in a pattern consistent with the storm‐time dynamics of the ionosphere and thermosphere. To a lesser extent, magnetic activity also alters the average radial component of the electric drift below L=3. A global picture for the average variations of the electric drift with Kp is provided as a function of L and MLT. It is the first tim. . .
Date: 04/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL077873 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL077873
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Authors: Coleman Tim, McCollough James, Young Shawn, and Rigler E. J.
Title: Operational Nowcasting of Electron Flux Levels in the Outer Zone of Earth's Radiation Belt
Abstract: We describe a lightweight, accurate nowcasting model for electron flux levels measured by the Van Allen probes. Largely motivated by Rigler et al. [2004], we turn to a time‐varying linear filter of previous flux levels and Kp. We train and test this model on data gathered from the 2.10 MeV channel of the Relativistic Electron‐Proton Telescope (REPT) sensor onboard the Van Allen probes. Dynamic linear models are a specific case of state space models, and can be made flexible enough to emulate the nonlinear behavior of particle fluxes within the radiation belts. Real‐time estimation of the parameters of the model is done using a Kalman Filter, where the state of the model is exactly the parameters. Nowcast performance is assessed against several baseline interpolation schemes. Our mode. . .
Date: 04/2018 Publisher: Space Weather DOI: 10.1029/2017SW001788 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2017SW001788
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Authors: Olifer L., Mann I. R., Morley S. K., Ozeke L. G., and Choi D.
Title: On the role of last closed drift shell dynamics in driving fast losses and Van Allen radiation belt extinction
Abstract: We present observations of very fast radiation belt loss as resolved using high‐time resolution electron flux data from the constellation of Global Positioning System (GPS) satellites. The timescale of these losses is revealed to be as short as ∼0.5 − 2 hours during intense magnetic storms, with some storms demonstrating almost total loss on these timescales and which we characterize as radiation belt extinction. The intense March 2013 and March 2015 storms both show such fast extinction, with a rapid recovery, while the September 2014 storm shows fast extinction but no recovery for around two weeks. By contrast, the moderate September 2012 storm which generated a three radiation belt morphology shows more gradual loss. We compute the last closed drift shell (LCDS) for each of these . . .
Date: 04/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025190 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025190
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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
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Authors: Agapitov O., Drake J. F., Vasko I., Mozer F S, Artemyev A., et al.
Title: Nonlinear Electrostatic Steepening of Whistler Waves: The Guiding Factors and Dynamics in Inhomogeneous Systems
Abstract: Whistler mode chorus waves are particularly important in outer radiation belt dynamics due to their key role in controlling the acceleration and scattering of electrons over a very wide energy range. The efficiency of wave‐particle resonant interactions is defined by whistler wave properties which have been described by the approximation of plane linear waves propagating through the cold plasma of the inner magnetosphere. However, recent observations of extremely high‐amplitude whistlers suggest the importance of nonlinear wave‐particle interactions for the dynamics of the outer radiation belt. Oblique chorus waves observed in the inner magnetosphere often exhibit drastically nonsinusoidal (with significant power in the higher harmonics) waveforms of the parallel electric field, pres. . .
Date: 03/2018 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL076957 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2017GL076957
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Authors: Ma Q, Li W, Bortnik J, Thorne R M, Chu X., et al.
Title: Quantitative Evaluation of Radial Diffusion and Local Acceleration Processes During GEM Challenge Events
Abstract: We simulate the radiation belt electron flux enhancements during selected Geospace Environment Modeling (GEM) challenge events to quantitatively compare the major processes involved in relativistic electron acceleration under different conditions. Van Allen Probes observed significant electron flux enhancement during both the storm time of 17–18 March 2013 and non–storm time of 19–20 September 2013, but the distributions of plasma waves and energetic electrons for the two events were dramatically different. During 17–18 March 2013, the SYM‐H minimum reached −130 nT, intense chorus waves (peak Bw ~140 pT) occurred at 3.5 < L < 5.5, and several hundred keV to several MeV electron fluxes increased by ~2 orders of magnitude mostly at 3.5 < L < 5.5. During 19–20 September 2013, th. . .
Date: 03/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA025114 Available at: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JA025114
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