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2016
Authors: Ozaki M., Shiokawa K., Miyoshi Y, Kataoka R., Yagitani S., et al.
Title: Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes
Abstract: To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8 s) images of proton-induced N2+ emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100 s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100 s and an unpredicted fast modulation of a few tens of sec. . .
Date: 08/2016 Publisher: Geophysical Research Letters Pages: 7859 - 7866 DOI: 10.1002/2016GL070008 Available at: http://doi.wiley.com/10.1002/2016GL070008
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Authors: Su Yi-Jiun, Selesnick Richard S., and Blake J B
Title: Formation of the inner electron radiation belt by enhanced large-scale electric fields
Abstract: A two-dimensional bounce-averaged test particle code was developed to examine trapped electron trajectories during geomagnetic storms with the assumption of conservation of the first and second adiabatic invariants. The March 2013 storm was selected as an example because the geomagnetic activity Kp index sharply increased from 2 + to 7− at 6:00 UT on 17 March. Electron measurements with energies between 37 and 460 keV from the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard Van Allen Probes (VAP) are used as initial conditions prior to the storm onset and served to validate test particle simulations during the storm. Simulation results help to interpret the observed electron injection as nondiffusive radial transport over a short distance in the inner belt and slot. . .
Date: 08/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022881 Available at: http://doi.wiley.com/10.1002/2016JA022881
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Authors: Aryan Homayon, Sibeck David, Balikhin Michael, Agapitov Oleksiy, and Kletzing Craig
Title: Observation of chorus waves by the Van Allen Probes: Dependence on solar wind parameters and scale size
Abstract: Highly energetic electrons in the Earth's Van Allen radiation belts can cause serious damage to spacecraft electronic systems and affect the atmospheric composition if they precipitate into the upper atmosphere. Whistler mode chorus waves have attracted significant attention in recent decades for their crucial role in the acceleration and loss of energetic electrons that ultimately change the dynamics of the radiation belts. The distribution of these waves in the inner magnetosphere is commonly presented as a function of geomagnetic activity. However, geomagnetic indices are nonspecific parameters that are compiled from imperfectly covered ground based measurements. The present study uses wave data from the two Van Allen Probes to present the distribution of lower band chorus waves not onl. . .
Date: 08/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 7608 - 7621 DOI: 10.1002/jgra.v121.810.1002/2016JA022775 Available at: http://doi.wiley.com/10.1002/2016JA022775
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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: Takahashi Kazue, Hartinger Michael D., Malaspina David M., Smith Charles W., Koga Kiyokazu, et al.
Title: Propagation of ULF waves from the upstream region to the midnight sector of the inner magnetosphere
Abstract: Ultralow frequency (ULF) waves generated in the ion foreshock are a well-known source of Pc3-Pc4 waves (7–100 mHz) observed in the dayside magnetosphere. We use data acquired on 10 April 2013 by multiple spacecraft to demonstrate that ULF waves of upstream origin can propagate to the midnight sector of the inner magnetosphere. At 1130–1730 UT on the selected day, the two Van Allen Probes spacecraft and the geostationary ETS-VIII satellite detected compressional 20 to 40 mHz magnetic field oscillations between L ∼ 4 and L ∼ 7 in the midnight sector, along with other spacecraft located closer to noon. Upstream origin of the oscillations is concluded from the wave frequency that matches a theoretical model, globally coherent amplitude modulation, and duskward propagation that is consi. . .
Date: 08/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022958 Available at: http://doi.wiley.com/10.1002/2016JA022958
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Authors: Yue Chao, An Xin, Bortnik Jacob, Ma Qianli, Li Wen, et al.
Title: The relationship between the macroscopic state of electrons and the properties of chorus waves observed by the Van Allen Probes
Abstract: Plasma kinetic theory predicts that a sufficiently anisotropic electron distribution will excite whistler mode waves, which in turn relax the electron distribution in such a way as to create an upper bound on the relaxed electron anisotropy. Here using whistler mode chorus wave and plasma measurements by Van Allen Probes, we confirm that the electron distributions are well constrained by this instability to a marginally stable state in the whistler mode chorus waves generation region. Lower band chorus waves are organized by the electron β∥e into two distinct groups: (i) relatively large-amplitude, quasi-parallel waves with inline image and (ii) relatively small-amplitude, oblique waves with inline image. The upper band chorus waves also have enhanced amplitudes close to the instabili. . .
Date: 08/2016 Publisher: Geophysical Research Letters Pages: 7804 - 7812 DOI: 10.1002/2016GL070084 Available at: http://doi.wiley.com/10.1002/2016GL070084
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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: Keika Kunihiro, Seki Kanako, é Masahito, Machida Shinobu, Miyoshi Yoshizumi, et al.
Title: Storm time impulsive enhancements of energetic oxygen due to adiabatic acceleration of preexisting warm oxygen in the inner magnetosphere
Abstract: We examine enhancements of energetic (>50 keV) oxygen ions observed by the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument on board the Van Allen Probes spacecraft in the inner magnetosphere (L ~ 6) at 22–23 h magnetic local time (MLT) during an injection event of the 6 June 2013 storm. Simultaneous observations by two Van Allen Probes spacecraft located close together (~0.5 RE) indicate that particle injections occurred in the premidnight sector (< ~24 h MLT). We also examine the evolution of the proton and oxygen energy spectra at L ~ 6 during the injection event. The spectral slope did not significantly change during the storm. The oxygen phase space density (PSD) was shifted toward higher PSD in a wide range of the first adiabatic invariant. . .
Date: 08/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 7739 - 7752 DOI: 10.1002/2016JA022384 Available at: http://doi.wiley.com/10.1002/2016JA022384
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Authors: Zhang X.-J., Li W, Ma Q, Thorne R M, Angelopoulos V, et al.
Title: Direct evidence for EMIC wave scattering of relativistic electrons in space
Abstract: Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes. EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022521 Available at: http://doi.wiley.com/10.1002/2016JA022521
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Authors: Li Zhao, Hudson Mary, Paral Jan, Wiltberger Michael, and Turner Drew
Title: Global ULF wave analysis of radial diffusion coefficients using a global MHD model for the 17 March 2015 storm
Abstract: The 17–18 March 2015 storm is the largest geomagnetic storm in the Van Allen Probes era to date. The Lyon-Fedder-Mobarry global MHD model has been run for this event using ARTEMIS data as solar wind input. The ULF wave power spectral density of the azimuthal electric field and compressional magnetic field is analyzed in the 0.5–8.3 mHz range. The lowest three azimuthal modes account for 70% of the total power during quiet times. However, during high activity, they are not exclusively dominant. The calculation of the radial diffusion coefficient is presented. We conclude that the electric field radial diffusion coefficient is dominant over the magnetic field coefficient by one to two orders of magnitude. This result contrasts with the dominant magnetic field diffusion coefficient used i. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022508 Available at: http://doi.wiley.com/10.1002/2016JA022508
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Authors: Yuan Zhigang, Yu Xiongdong, Wang Dedong, Huang Shiyong, Li Haimeng, et al.
Title: In situ evidence of the modification of the parallel propagation of EMIC waves by heated He + ions
Abstract: With observations of the Van Allen Probe B, we report in situ evidence of the modification of the parallel propagating electromagnetic ion cyclotron (EMIC) waves by heated He+ ions. In the outer boundary of the plasmasphere, accompanied with the He+ ion heating, the frequency bands of H+ and He+ for EMIC waves merged into each other, leading to the disappearance of a usual stop band between the gyrofrequency of He+ ions (ΩHe+) and the H+ cutoff frequency (ωH+co) in the cold plasma. Moreover, the dispersion relation for EMIC waves theoretically calculated with the observed plasma parameters also demonstrates that EMIC waves can indeed parallel propagate across ΩHe+. Therefore, the paper provides an in situ evidence of the modification of the parallel propagation of EMIC waves by heated H. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022573 Available at: http://doi.wiley.com/10.1002/2016JA022573
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Authors: O'Brien T P, Claudepierre S G, Guild T B, Fennell J. F., Turner D. L., et al.
Title: Inner zone and slot electron radial diffusion revisited
Abstract: Using recent data from NASA's Van Allen Probes, we estimate the quiet time radial diffusion coefficients for electrons in the inner radiation belt (L < 3) with energies from ~50 to 750 keV. The observations are consistent with dynamics dominated by pitch angle scattering and radial diffusion. We use a coordinate system in which these two modes of diffusion are separable. Then we integrate phase space density over pitch angle to obtain a “bundle content” that is invariant to pitch angle scattering, except for atmospheric loss. We estimate the effective radial diffusion coefficient from the temporal and radial variation of the bundle content. We show that our diffusion coefficients agree well with previously determined values obtained in the 1960s and 1970s and follow the form one . . .
Date: 07/2016 Publisher: Geophysical Research Letters Pages: 7301 - 7310 DOI: 10.1002/2016GL069749 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL069749/full
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Authors: Sarno-Smith Lois K., Liemohn Michael W., Skoug Ruth M., Larsen Brian A., Moldwin Mark B., et al.
Title: Local time variations of high-energy plasmaspheric ion pitch angle distributions
Abstract: Recent observations from the Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument revealed a persistent depletion in the 1–10 eV ion population in the postmidnight sector during quiet times in the 2 < L < 3 region. This study explores the source of this ion depletion by developing an algorithm to classify 26 months of pitch angle distributions measured by the HOPE instrument. We correct the HOPE low energy fluxes for spacecraft potential using measurements from the Electric Field and Waves (EFW) instrument. A high percentage of low count pitch angle distributions is found in the postmidnight sector coupled with a low percentage of ion distributions peaked perpendicular to the field line. A peak in loss cone distributions in the dusk sector is also observed. These results char. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA022301 Available at: http://doi.wiley.com/10.1002/2015JA022301
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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: 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: Lejosne Solène, and Mozer F S
Title: Van Allen Probe measurements of the electric drift E × B/B2 at Arecibo's L = 1.4 field line coordinate
Abstract: We have used electric and magnetic measurements by Van Allen Probe B from 2013 to 2014 to examine the equatorial electric drift E × B/B2 at one field line coordinate set to Arecibo's incoherent scatter radar location (L = 1.43). We report on departures from the traditional picture of corotational motion with the Earth in two ways: (1) the rotational angular speed is found to be 10% smaller than the rotational angular speed of the Earth, in agreement with previous works on plasmaspheric notches, and (2) the equatorial electric drift displays a dependence in magnetic local time, with a pattern consistent with the mapping of the Arecibo ionosphere dynamo electric fields along equipotential magnetic field lines. The electric fields due to the ionosphere dynamo are therefore expected t. . .
Date: 07/2016 Publisher: Geophysical Research Letters Pages: 6768 - 6774 DOI: 10.1002/2016GL069875 Available at: http://doi.wiley.com/10.1002/2016GL069875
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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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Authors: Sarris Theodore E., and Li Xinlin
Title: Calculating ultra-low-frequency wave power of the compressional magnetic field vs. L and time: multi-spacecraft analysis using the Van Allen probes, THEMIS and GOES
Abstract: Ultra-low-frequency (ULF) pulsations are critical in radial diffusion processes of energetic particles, and the power spectral density (PSD) of these fluctuations is an integral part of the radial diffusion coefficients and of assimilative models of the radiation belts. Using simultaneous measurements from two Geostationary Operational Environmental Satellites (GOES) geosynchronous satellites, three satellites of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft constellation and the two Van Allen probes during a 10-day period of intense geomagnetic activity and ULF pulsations of October 2012, we calculate the PSDs of ULF pulsations at different L shells. By following the time history of measurements at different L it is shown that, during this tim. . .
Date: 06/2016 Publisher: Annales Geophysicae Pages: 565 - 571 DOI: 10.5194/angeo-34-565-2016 Available at: http://www.ann-geophys.net/34/565/2016/
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Authors: Martinez-Calderon Claudia, Shiokawa Kazuo, Miyoshi Yoshizumi, Keika Kunihiro, Ozaki Mitsunori, et al.
Title: ELF/VLF wave propagation at subauroral latitudes: Conjugate observation between the ground and Van Allen Probes A
Abstract: We report simultaneous observation of ELF/VLF emissions, showing similar spectral and frequency features, between a VLF receiver at Athabasca (ATH), Canada, (L = 4.3) and Van Allen Probes A (Radiation Belt Storm Probes (RBSP) A). Using a statistical database from 1 November 2012 to 31 October 2013, we compared a total of 347 emissions observed on the ground with observations made by RBSP in the magnetosphere. On 25 February 2013, from 12:46 to 13:39 UT in the dawn sector (04–06 magnetic local time (MLT)), we observed a quasiperiodic (QP) emission centered at 4 kHz, and an accompanying short pulse lasting less than a second at 4.8 kHz in the dawn sector (04–06 MLT). RBSP A wave data showed both emissions as right-hand polarized with their Poynting vector earthward to the Northern Hemisp. . .
Date: 06/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 5384 - 5393 DOI: 10.1002/jgra.v121.610.1002/2015JA022264 Available at: http://doi.wiley.com/10.1002/2015JA022264
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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: Mann Ian R., and Ozeke Louis G.
Title: How quickly, how deeply, and how strongly can dynamical outer boundary conditions impact Van Allen radiation belt morphology?
Abstract: Here we examine the speed, strength, and depth of the coupling between dynamical variations of ultrarelativistic electron flux at the outer boundary and that in the heart of the outer radiation belt. Using ULF wave radial diffusion as an exemplar, we show how changing boundary conditions can completely change belt morphology even under conditions of identical wave power. In the case of ULF wave radial diffusion, the temporal dynamics of a new source population or a sink of electron flux at the outer plasma sheet boundary can generate a completely opposite response which reaches deep into the belt under identical ULF wave conditions. Very significantly, here we show that such coupling can occur on timescales much faster than previously thought. We show that even on timescales ~1 h, change. . .
Date: 06/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 5553 - 5558 DOI: 10.1002/jgra.v121.610.1002/2016JA022647 Available at: http://doi.wiley.com/10.1002/2016JA022647
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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: Foster J. C., Erickson P. J., Baker D N, Jaynes A. N., Mishin E. V., et al.
Title: Observations of the impenetrable barrier, the plasmapause, and the VLF bubble during the 17 March 2015 storm
Abstract: Van Allen Probes observations during the 17 March 2015 major geomagnetic storm strongly suggest that VLF transmitter-induced waves play an important role in sculpting the earthward extent of outer zone MeV electrons. A magnetically confined bubble of very low frequency (VLF) wave emissions of terrestrial, human-produced origin surrounds the Earth. The outer limit of the VLF bubble closely matches the position of an apparent barrier to the inward extent of multi-MeV radiation belt electrons near 2.8 Earth radii. When the VLF transmitter signals extend beyond the eroded plasmapause, electron loss processes set up near the outer extent of the VLF bubble create an earthward limit to the region of local acceleration near L = 2.8 as MeV electrons are scattered into the atmospheric loss cone.
Date: 06/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 5537 - 5548 DOI: 10.1002/jgra.v121.610.1002/2016JA022509 Available at: http://doi.wiley.com/10.1002/2016JA022509
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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: Yue Chao, Li Wen, Nishimura Yukitoshi, Zong Qiugang, Ma Qianli, et al.
Title: Rapid enhancement of low-energy (<100 eV) ion flux in response to interplanetary shocks based on two Van Allen Probes case studies: Implications for source regions and heating mechanisms
Abstract: Interactions between interplanetary (IP) shocks and the Earth's magnetosphere manifest many important space physics phenomena including low-energy ion flux enhancements and particle acceleration. In order to investigate the mechanisms driving shock-induced enhancement of low-energy ion flux, we have examined two IP shock events that occurred when the Van Allen Probes were located near the equator while ionospheric and ground observations were available around the spacecraft footprints. We have found that, associated with the shock arrival, electromagnetic fields intensified, and low-energy ion fluxes, including H+, He+, and O+, were enhanced dramatically in both the parallel and perpendicular directions. During the 2 October 2013 shock event, both parallel and perpendicular flux enhancemen. . .
Date: 06/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022808 Available at: http://doi.wiley.com/10.1002/2016JA022808
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Authors: Baker D N, Jaynes A. N., Turner D. L., Nakamura R, Schmid D., et al.
Title: A telescopic and microscopic examination of acceleration in the June 2015 geomagnetic storm: Magnetospheric Multiscale and Van Allen Probes study of substorm particle injection
Abstract: An active storm period in June 2015 showed that particle injection events seen sequentially by the four (Magnetospheric Multiscale) MMS spacecraft subsequently fed the enhancement of the outer radiation belt observed by Van Allen Probes mission sensors. Several episodes of significant southward interplanetary magnetic field along with a period of high solar wind speed (Vsw ≳ 500 km/s) on 22 June occurred following strong interplanetary shock wave impacts on the magnetosphere. Key events on 22 June 2015 show that the magnetosphere progressed through a sequence of energy-loading and stress-developing states until the entire system suddenly reconfigured at 19:32 UT. Energetic electrons, plasma, and magnetic fields measured by the four MMS spacecraft revealed clear dipolarization front. . .
Date: 06/2016 Publisher: Geophysical Research Letters Pages: 6051 - 6059 DOI: 10.1002/grl.v43.1210.1002/2016GL069643 Available at: http://doi.wiley.com/10.1002/2016GL069643
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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: Zhelavskaya I. S., Spasojevic M., Shprits Y Y, and Kurth W S
Title: Automated determination of electron density from electric field measurements on the Van Allen Probes spacecraft
Abstract: We present the Neural-network-based Upper hybrid Resonance Determination (NURD) algorithm for automatic inference of the electron number density from plasma wave measurements made on board NASA's Van Allen Probes mission. A feedforward neural network is developed to determine the upper hybrid resonance frequency, fuhr, from electric field measurements, which is then used to calculate the electron number density. In previous missions, the plasma resonance bands were manually identified, and there have been few attempts to do robust, routine automated detections. We describe the design and implementation of the algorithm and perform an initial analysis of the resulting electron number density distribution obtained by applying NURD to 2.5 years of data collected with the Electric and Magnetic. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA022132 Available at: http://doi.wiley.com/10.1002/2015JA022132
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Authors: Kistler L.M., Mouikis C. G., Spence H.E., Menz A.M., Skoug R.M., et al.
Title: The Source of O + in the Storm-time Ring Current
Abstract: A stretched and compressed geomagnetic field occurred during the main phase of a geomagnetic storm on 1 June 2013. During the storm the Van Allen Probes spacecraft made measurements of the plasma sheet boundary layer, and observed large fluxes of O+ ions streaming up the field line from the nightside auroral region. Prior to the storm main phase there was an increase in the hot (>1 keV) and more isotropic O+ions in the plasma sheet. In the spacecraft inbound pass through the ring current region during the storm main phase, the H+ and O+ ions were significantly enhanced. We show that this enhanced inner magnetosphere ring current population is due to the inward adiabatic convection of the plasma sheet ion population. The energy range of the O+ ion plasma sheet that impacts the ring curren. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA022204 Available at: http://doi.wiley.com/10.1002/2015JA022204
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Authors: He Fengming, Cao Xing, Ni Binbin, Xiang Zheng, Zhou Chen, et al.
Title: Combined Scattering Loss of Radiation Belt Relativistic Electrons by Simultaneous Three-band EMIC Waves: A Case Study
Abstract: Multiband electromagnetic ion cyclotron (EMIC) waves can drive efficient scattering loss of radiation belt relativistic electrons. However, it is statistically uncommon to capture the three bands of EMIC waves concurrently. Utilizing data from the Electric and Magnetic Field Instrument Suite and Integrated Science magnetometer onboard Van Allen Probe A, we report the simultaneous presence of three (H+, He+, and O+) emission bands in an EMIC wave event, which provides an opportunity to look into the combined scattering effect of all EMIC emissions and the relative roles of each band in diffusing radiation belt relativistic electrons under realistic circumstances. Our quantitative results, obtained by quasi-linear diffusion rate computations and 1-D pure pitch angle diffusion simulations, de. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022483 Available at: http://doi.wiley.com/10.1002/2016JA022483
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Authors: Liu H., Zong Q.-G., Zhou X.-Z., Fu S. Y., Rankin R, et al.
Title: Compressional ULF wave modulation of energetic particles in the inner magnetosphere
Abstract: We present Van Allen Probes observations of modulations in the flux of very energetic electrons up to a few MeV and protons between 1200 − 1400 UT on February 19th, 2014. During this event the spacecraft were in the dayside magnetosphere at L⋆≈5.5. The modulations extended across a wide range of particle energies, from 79.80 keV to 2.85 MeV for electrons and from 82.85 keV to 636.18 keV for protons. The fluxes of π/2 pitch angle particles were observed to attain maximum values simultaneously with the ULF compressional magnetic field component reaching a minimum. We use peak-to-valley ratios to quantify the strength of the modulation effect, finding that the modulation is larger at higher energies than at lower energies. It is shown that the compressional wave modulation of the parti. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022706 Available at: http://doi.wiley.com/10.1002/2016JA022706
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Authors: Saikin A. A., Zhang J. -C., Smith C W, Spence H E, Torbert R B, et al.
Title: The dependence on geomagnetic conditions and solar wind dynamic pressure of the spatial distributions of EMIC waves observed by the Van Allen Probes
Abstract: A statistical examination on the spatial distributions of electromagnetic ion cyclotron (EMIC) waves observed by the Van Allen Probes against varying levels of geomagnetic activity (i.e., AE and SYM-H) and dynamic pressure has been performed. Measurements taken by the Electric and Magnetic Field Instrument Suite and Integrated Science for the first full magnetic local time (MLT) precession of the Van Allen Probes (September 2012–June 2014) are used to identify over 700 EMIC wave events. Spatial distributions of EMIC waves are found to vary depending on the level of geomagnetic activity and solar wind dynamic pressure. EMIC wave events were observed under quiet (AE ≤ 100 nT, 325 wave events), moderate (100 nT < AE ≤ 300 nT, 218 wave events), and disturbed (AE > 3. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022523 Available at: http://doi.wiley.com/10.1002/2016JA022523
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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: Blum L. W., Agapitov O., Bonnell J. W., Kletzing C., and Wygant J
Title: EMIC wave spatial and coherence scales as determined from multipoint Van Allen Probe measurements
Abstract: Electromagnetic ion cyclotron (EMIC) waves can provide a strong source of energetic electron pitch angle scattering. These waves are often quite localized, thus their spatial extent can have a large effect on their overall scattering efficiency. Using measurements from the dual Van Allen Probes, we examine four EMIC wave events observed simultaneously on the two probes at varying spacecraft separations. Correlation of both the wave amplitude and phase observed at both spacecraft is examined to estimate the active region and coherence scales of the waves. We find well-correlated wave amplitude and amplitude modulation across distances spanning hundreds to thousands of kilometers. Phase coherence persisting 30–60 s is observable during close conjunction events but is lost as spacecraft s. . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL068799 Available at: http://doi.wiley.com/10.1002/2016GL068799
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Authors: 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: Califf S., Li X, Wolf R. A., Zhao H., Jaynes A. N., et al.
Title: Large-amplitude electric fields in the inner magnetosphere: Van Allen Probes observations of subauroral polarization streams
Abstract: The subauroral polarization stream (SAPS) is an important magnetosphere-ionosphere (MI) coupling phenomenon that impacts a range of particle populations in the inner magnetosphere. SAPS studies often emphasize ionospheric signatures of fast westward flows, but the equatorial magnetosphere is also affected through strong radial electric fields in the dusk sector. This study focuses on a period of steady southward interplanetary magnetic field (IMF) during the 29 June 2013 geomagnetic storm where the Van Allen Probes observe a region of intense electric fields near the plasmapause over multiple consecutive outbound duskside passes. We show that the large-amplitude electric fields near the equatorial plane are consistent with SAPS by investigating the relationship between plasma sheet ion and. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA022252 Available at: http://doi.wiley.com/10.1002/2015JA022252
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Authors: Reiff P. H., Daou A. G., Sazykin S. Y., Nakamura R, Hairston M. R., et al.
Title: Multispacecraft Observations and Modeling of the June 22/23, 2015 Geomagnetic Storm
Abstract: The magnetic storm of June 22-23, 2015 was one of the largest in the current solar cycle. We present in situ observations from the Magnetospheric Multiscale Mission (MMS) and the Van Allen Probes (VAP) in the magnetotail, field-aligned currents from AMPERE, and ionospheric flow data from DMSP. Our real-time space weather alert system sent out a “red alert”, correctly predicting Kp indices greater than 8. We show strong outflow of ionospheric Oxygen, dipolarizations in the MMS magnetometer data, and dropouts in the particle fluxes seen by the MMS FPI instrument suite. At ionospheric altitudes, the AMPERE data show highly variable currents exceeding 20 MA. We present numerical simulations with the BATS-R-US global magnetohydrodynamic (MHD) model linked with the Rice Convection Model (RCM. . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL069154 Available at: http://doi.wiley.com/10.1002/2016GL069154
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Authors: Li W, Santolik O, Bortnik J, Thorne R M, Kletzing C A, et al.
Title: New Chorus Wave Properties Near the Equator from Van Allen Probes Wave Observations
Abstract: The chorus wave properties are evaluated using Van Allen Probes data in the Earth's equatorial magnetosphere. Two distinct modes of lower band chorus are identified: a quasi-parallel mode and a quasi-electrostatic mode, whose wave normal direction is close to the resonance cone. Statistical results indicate that the quasi-electrostatic (quasi-parallel) mode preferentially occurs during relatively quiet (disturbed) geomagnetic activity at lower (higher) L shells. Although the magnetic intensity of the quasi-electrostatic mode is considerably weaker than the quasi-parallel mode, their electric intensities are comparable. A newly identified feature of the quasi-electrostatic mode is that its frequency peaks at higher values compared to the quasi-parallel mode that exhibits a broad frequency s. . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL068780 Available at: http://doi.wiley.com/10.1002/2016GL068780
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Authors: Burke W. J., Erickson P. J., Yang J., Foster J., Wygant J, et al.
Title: O + Ion Conic and Plasma Sheet Dynamics Observed by Van Allen Probe Satellites during the 1 June 2013 Magnetic Storm
Abstract: The Van Allen Probe satellites were near apogee in the late evening local time sector during the 1 June 2013 magnetic storm's main phase. About an hour after crossing the ring current's “nose structure” into the plasma sheet, the satellites encountered a quasi-periodic sequence of 0.08 - 3 keV O+ ions. Pitch angle distributions of this population consistently peaked nearly anti-parallel to the local magnetic field. We interpret this population as O+ conics originating in the northern ionosphere. Sequences began as fairly steady state conic fluxes with energies in the ~ 80 to 100 eV range. Over about a half hour build-up phase, O+ energies peaked near 1 keV. During subsequent release phases lasting ~ 20 minutes, O+ energies returned to low-energy starting points. We argu. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021795 Available at: http://doi.wiley.com/10.1002/2015JA021795
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Authors: Ni Binbin, Zou Zhengyang, Li Xinlin, Bortnik Jacob, Xie Lun, et al.
Title: Occurrence Characteristics of Outer Zone Relativistic Electron Butterfly Distribution: A Survey of Van Allen Probes REPT Measurements
Abstract: Using Van Allen Probes REPT pitch angle resolved electron flux data from September 2012 to March 2015, we investigate in detail the global occurrence pattern of equatorial (|λ| ≤ 3°) butterfly distribution of outer zone relativistic electrons and its potential correlation with the solar wind dynamic pressure. The statistical results demonstrate that these butterfly distributions occur with the highest occurrence rate ~ 80% at ~ 20 – 04 MLT and L > ~ 5.5 and with the second peak (> ~ 50 %) at ~ 11 – 15 MLT of lower L-shells ~ 4.0. They can also extend to L = 3.5 and to other MLT intervals but with the occurrence rates predominantly < ~25%. It is further shown that outer zone relativistic electron butterfly distributions are likely to peak between . . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL069350 Available at: http://doi.wiley.com/10.1002/2016GL069350
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Authors: Ripoll J. F., Reeves G., Cunningham G., Loridan V., Denton M., et al.
Title: Reproducing the observed energy-dependent structure of Earth's electron radiation belts during storm recovery with an event-specific diffusion model
Abstract: We present dynamic simulations of energy-dependent losses in the radiation belt " slot region" and the formation of the two-belt structure for the quiet days after the March 1st storm. The simulations combine radial diffusion with a realistic scattering model, based data-driven spatially and temporally-resolved whistler mode hiss wave observations from the Van Allen Probes satellites. The simulations reproduce Van Allen Probes observations for all energies and L-shells (2 to 6) including (a) the strong energy-dependence to the radiation belt dynamics (b) an energy-dependent outer boundary to the inner zone that extends to higher L-shells at lower energies and (c) an " S-shaped" energy-dependent inner boundary to the outer zone that results from the competition between diffusive radial tran. . .
Date: 05/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL068869 Available at: http://doi.wiley.com/10.1002/2016GL068869
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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: Shi Run, Summers Danny, Ni Binbin, Manweiler Jerry W., Mitchell Donald G., et al.
Title: A statistical study of proton pitch angle distributions measured by the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE)
Abstract: A statistical study of ring current-energy proton pitch angle distributions (PADs) in Earth's inner magnetosphere is reported here. The data are from the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on board the Van Allen Probe B spacecraft from January 1, 2013 to April 15, 2015. By fitting the data to the functional form sinnα, where α is the proton pitch angle, we examine proton PADs at the energies 50, 100, 180, 328 and 488 keV in the L-shell range from L = 2.5 to L = 6. Three PAD types are classified: trapped (90° peaked), butterfly and isotropic. The proton PAD dependence on the particle energy, MLT, L-shell, and geomagnetic activity are analyzed in detail. The results show a strong dependence of the proton PADs on MLT. On the nightside, the n values o. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA022140 Available at: http://doi.wiley.com/10.1002/2015JA022140
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Authors: Gkioulidou Matina, Ukhorskiy A., Mitchell D G, and Lanzerotti L J
Title: Storm-time dynamics of ring current protons: Implications for the long-term energy budget in the inner magnetosphere
Abstract: Our investigation of the long-term ring current proton pressure evolution in Earth's inner magnetosphere based on Van Allen Probes data shows drastically different behavior of the low- and high- energy components of the ring current proton population with respect to theSYM-H index variation. We found that while the low-energy component of the protons (<80 keV) is strongly governed by convective timescales and is very well correlated with the absolute value of SYM-H index, the high-energy component (>100 keV) varies on much longer timescales and shows either no correlation or anticorrelation with the absolute value of SYM-H index. Our study also shows that the contributions of the low- and high- energy protons to the inner magnetosphere energy content are comparable. Thus, our results c. . .
Date: 05/2016 Publisher: Geophysical Research Letters Pages: n/a - n/a DOI: 10.1002/2016GL068013 Available at: http://doi.wiley.com/10.1002/2016GL068013
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Authors: Liu Y., Zong Q.-G., Zhou X.-Z., Foster J. C., and Rankin R
Title: Structure and Evolution of Electron "Zebra Stripes" in the Inner Radiation Belt
Abstract: Zebra stripes” are newly found energetic electron energy-spatial (L shell) distributed structure with an energy between tens to a few hundreds keV in the inner radiation belt. Using high-quality measurements of electron fluxes from Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on board the twin Van Allen Probes, we carry out case and statistical studies from April 2013 to April 2014 to study the structural and evolutionary characteristics of zebra stripes below L = 3. It is revealed that the zebra stripes can be transformed into evenly spaced patterns in the electron drift frequency coordinate: the detrended logarithmic fluxes in each L shell region can be well described by sinusoidal functions of drift frequency. The “wave number” of this sinusoidal function, whic. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA022077 Available at: http://doi.wiley.com/10.1002/2015JA022077
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Authors: Kessel Mona
Title: Things we don't yet understand about solar driving of the radiation belts.
Abstract: This commentary explores how close we are to predicting the behavior of the radiations belts - the primary science objective of NASA's Van Allen Probes mission. Starting with what we know or think we know about competing sources, enhancement, transport, and loss, I walk through recent papers that have improved our understanding and then focus on flux dropouts as one particular yardstick of success. I mention a new paradigm for electrons and the importance of reliably matching models and observations for different solar inputs. Although the case for prediction remains a work in progress, there are encouraging signs of progress.
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022472 Available at: http://doi.wiley.com/10.1002/2016JA022472
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Authors: Hartley D. P., Kletzing C A, Kurth W S, Bounds S R, Averkamp T. F., et al.
Title: Using the cold plasma dispersion relation and whistler-mode waves to quantify the antenna sheath impedance of the Van Allen Probes EFW instrument
Abstract: Cold plasma theory and parallel wave propagation are often assumed when approximating the whistler mode magnetic field wave power from electric field observations. The current study is the first to include the wave normal angle from the Electric and Magnetic Field Instrument Suite and Integrated Science package on board the Van Allen Probes in the conversion factor, thus allowing for the accuracy of these assumptions to be quantified. Results indicate that removing the assumption of parallel propagation does not significantly affect calculated plasmaspheric hiss wave powers. Hence, the assumption of parallel propagation is valid. For chorus waves, inclusion of the wave normal angle in the conversion factor leads to significant alterations in the distribution of wave power ratios (observed/. . .
Date: 05/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022501 Available at: http://doi.wiley.com/10.1002/2016JA022501
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Authors: Halford A J, McGregor S. L., Hudson M K, Millan R M, and Kress B T
Title: BARREL observations of a Solar Energetic Electron and Solar Energetic Proton event
Abstract: During the second Balloon Array for Radiation Belt Relativistic Electron Losses (BARREL) campaign two solar energetic proton (SEP) events were observed. Although BARREL was designed to observe X-rays created during electron precipitation events, it is sensitive to X-rays from other sources. The gamma lines produced when energetic protons hit the upper atmosphere are used in this paper to study SEP events. During the second SEP event starting on 7 January 2014 and lasting ∼ 3 days, which also had a solar energetic electron (SEE) event occurring simultaneously, BARREL had 6 payloads afloat spanning all MLT sectors and L-values. Three payloads were in a tight array (∼ 2 hrs in MLT and ∼ 2 Δ L) inside the inner magnetosphere and at times conjugate in both L and MLT with the Van Allen Pr. . .
Date: 04/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: n/a - n/a DOI: 10.1002/2016JA022462 Available at: http://doi.wiley.com/10.1002/2016JA022462http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2016JA022462
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Authors: Maldonado Armando A., Chen Lunjin, Claudepierre Seth G., Bortnik Jacob, Thorne Richard M, et al.
Title: Electron butterfly distribution modulation by magnetosonic waves
Abstract: The butterfly pitch angle distribution is observed as a dip in an otherwise normal distribution of electrons centered about αeq=90°. During storm times, the formation of the butterfly distribution on the nightside magnetosphere has been attributed to L shell splitting combined with magnetopause shadowing and strong positive radial flux gradients. It has been shown that this distribution can be caused by combined chorus and magnetosonic wave scattering where the two waves work together but at different local times. Presented in our study is an event on 21 August 2013, using Van Allen Probe measurements, where a butterfly distribution formation is modulated by local magnetosonic coherent magnetosonic waves intensity. Transition from normal to butterfly distributions coincides with rising m. . .
Date: 04/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL068161 Available at: http://doi.wiley.com/10.1002/2016GL068161http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2016GL068161http://api.wiley.com/onlinelibrary/chorus/v1/articles/10.1002%2F2016GL068161
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Authors: Li Jinxing, Ni Binbin, Ma Qianli, Xie Lun, Pu Zuyin, et al.
Title: Formation of Energetic Electron Butterfly Distributions by Magnetosonic Waves via Landau Resonance
Abstract: Radiation belt electrons can exhibit different types of pitch angle distributions in response to various magnetospheric processes. Butterfly distributions, characterized by flux minima at pitch angles around 90°, are broadly observed in both the outer and inner belts and the slot region. Butterfly distributions close to the outer magnetospheric boundary have been attributed to drift shell splitting and losses to the magnetopause. However, their occurrence in the inner belt and the slot region has hitherto not been resolved. By analyzing the particle and wave data collected by the Van Allen Probes during a geomagnetic storm, we combine test particle calculations and Fokker-Planck simulations to reveal that scattering by equatorial magnetosonic waves is a significant cause for the formation. . .
Date: 04/2016 Publisher: Geophysical Research Letters Pages: n/a - n/a DOI: 10.1002/2016GL067853 Available at: http://doi.wiley.com/10.1002/2016GL067853http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2016GL067853
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