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2015
Authors: Su Zhenpeng, Zhu Hui, Xiao Fuliang, Zheng Huinan, Wang Yuming, et al.
Title: Disappearance of plasmaspheric hiss following interplanetary shock
Abstract: Plasmaspheric hiss is one of the important plasma waves controlling radiation belt dynamics. Its spatiotemporal distribution and generation mechanism are presently the object of active research. We here give the first report on the shock-induced disappearance of plasmaspheric hiss observed by the Van Allen Probes on 8 October 2013. This special event exhibits the dramatic variability of plasmaspheric hiss and provides a good opportunity to test its generation mechanisms. The origination of plasmaspheric hiss from plasmatrough chorus is suggested to be an appropriate prerequisite to explain this event. The shock increased the suprathermal electron fluxes, and then the enhanced Landau damping promptly prevented chorus waves from entering the plasmasphere. Subsequently, the shrinking magnetop. . .
Date: 03/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL063906 Available at: http://doi.wiley.com/10.1002/2015GL063906
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Authors: Miyoshi Y, Oyama S., Saito S., Kurita S., Fujiwara H., et al.
Title: Energetic electron precipitation associated with pulsating aurora: EISCAT and Van Allen Probe observations
Abstract: Pulsating auroras show quasi-periodic intensity modulations caused by the precipitation of energetic electrons of the order of tens of keV. It is expected theoretically that not only these electrons but also sub-relativistic/relativistic electrons precipitate simultaneously into the ionosphere owing to whistler-mode wave–particle interactions. The height-resolved electron density profile was observed with the European Incoherent Scatter (EISCAT) Tromsø VHF radar on 17 November 2012. Electron density enhancements were clearly identified at altitudes >68 km in association with the pulsating aurora, suggesting precipitation of electrons with a broadband energy range from ~10 keV up to at least 200 keV. The riometer and network of subionospheric radio wave observations also showed the energ. . .
Date: 03/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020690 Available at: http://doi.wiley.com/10.1002/2014JA020690
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Authors: Ukhorskiy A Y, Sitnov M I, Millan R M, Kress B T, Fennell J. F., et al.
Title: Global Storm-Time Depletion of the Outer Electron Belt
Abstract: The outer radiation belt consists of relativistic (>0.5 MeV) electrons trapped on closed trajectories around Earth where the magnetic field is nearly dipolar. During increased geomagnetic activity, electron intensities in the belt can vary by ordersof magnitude at different spatial and temporal scale. The main phase of geomagnetic storms often produces deep depletions of electron intensities over broad regions of the outer belt. Previous studies identified three possible processes that can contribute to the main-phase depletions: adiabatic inflation of electron drift orbits caused by the ring current growth, electron loss into the atmosphere, and electron escape through the magnetopause boundary. In this paper we investigate the relative importance of the adiabatic effect and magnetopause . . .
Date: 03/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020645 Available at: http://doi.wiley.com/10.1002/2014JA020645
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Authors: Sarno-Smith Lois K., Liemohn Michael W., Katus Roxanne M., Skoug Ruth M., Larsen Brian A., et al.
Title: Postmidnight depletion of the high-energy tail of the quiet plasmasphere
Abstract: The Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument measures the high-energy tail of the thermal plasmasphere allowing study of topside ionosphere and inner magnetosphere coupling. We statistically analyze a 22 month period of HOPE data, looking at quiet times with a Kp index of less than 3. We investigate the high-energy range of the plasmasphere, which consists of ions at energies between 1 and 10 eV and contains approximately 5% of total plasmaspheric density. Both the fluxes and partial plasma densities over this energy range show H+ is depleted the most in the postmidnight sector (1–4 magnetic local time), followed by O+ and then He+. The relative depletion of each species across the postmidnight sector is not ordered by mass, which reveals ionospheric influence. We. . .
Date: 03/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020682 Available at: http://doi.wiley.com/10.1002/2014JA020682
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Authors: Min Kyungguk, Liu Kaijun, Bonnell John W., Breneman Aaron W., Denton Richard E, et al.
Title: Study of EMIC wave excitation using direct ion measurements
Abstract: With data from Van Allen Probes, we investigate EMIC wave excitation using simultaneously observed ion distributions. Strong He-band waves occurred while the spacecraft was moving through an enhanced density region. We extract from Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer measurement the velocity distributions of warm heavy ions as well as anisotropic energetic protons that drive wave growth through the ion cyclotron instability. Fitting the measured ion fluxes to multiple sinm-type distribution functions, we find that the observed ions make up about 15% of the total ions, but about 85% of them are still missing. By making legitimate estimates of the unseen cold (below ~2 eV) ion composition from cutoff frequencies suggested by the observed wave spectrum, a series of. . .
Date: 03/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020717 Available at: http://doi.wiley.com/10.1002/2014JA020717
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Authors: Kirby Karen, Fretz Kristin, Goldsten John, and Maurer Richard
Title: Successes and challenges of operating the Van Allen Probes mission in the radiation belts
Abstract: The Van Allen probes team has been successful in monitoring and trending the performance of the mission to date. However, operating two spacecraft in the Van Allen radiation belts poses a number of challenges and requires careful monitoring of spacecraft performance due to the high radiation environment and potential impact on the mostly single string electronics architecture. Spacecraft and instrument telemetry trending is tracked with internal peer reviews conducted twice a year by the operations and engineering teams. On board radiation monitoring sensors are used to evaluate total dose accumulated on board the spacecraft and to assess potential impacts. Single event upsets are tracked and high activity events are logged and analyzed. Anomalous data is compared to radiation and solar ev. . .
Date: 03/2015 Publisher: IEEE DOI: 10.1109/AERO.2015.7119179 Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=7119179
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Authors: Hartley D. P., Chen Y., Kletzing C A, Denton M. H., and Kurth W S
Title: Applying the cold plasma dispersion relation to whistler mode chorus waves: EMFISIS wave measurements from the Van Allen Probes
Abstract: Most theoretical wave models require the power in the wave magnetic field in order to determine the effect of chorus waves on radiation belt electrons. However, researchers typically use the cold plasma dispersion relation to approximate the magnetic wave power when only electric field data are available. In this study, the validity of using the cold plasma dispersion relation in this context is tested using Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations of both the electric and magnetic spectral intensities in the chorus wave band (0.1–0.9 fce). Results from this study indicate that the calculated wave intensity is least accurate during periods of enhanced wave activity. For observed wave intensities >10−3 nT2, using the cold plasma dispersi. . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020808 Available at: http://doi.wiley.com/10.1002/2014JA020808
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Authors: Turner D. L., Claudepierre S G, Fennell J. F., O'Brien T P, Blake J B, et al.
Title: Energetic electron injections deep into the inner magnetosphere associated with substorm activity
Abstract: From a survey of the first nightside season of NASA's Van Allen Probes mission (Dec/2012 – Sep/2013), 47 energetic (10s to 100s of keV) electron injection events were found at L-shells ≤ 4, all of which are deeper than any previously reported substorm-related injections. Preliminary details from these events are presented, including how: all occurred shortly after dipolarization signatures and injections were observed at higher L-shells; the deepest observed injection was at L~2.5; and, surprisingly, L≤4 injections are limited in energy to ≤250 keV. We present a detailed case study of one example event revealing that the injection of electrons down to L~3.5 was different from injections observed at higher L and likely resulted from drift resonance with a fast magnetosonic wave in t. . .
Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL063225 Available at: http://doi.wiley.com/10.1002/2015GL063225
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Authors: Nosé M., Oimatsu S., Keika K, Kletzing C A, Kurth W S, et al.
Title: Formation of the oxygen torus in the inner magnetosphere: Van Allen Probes observations
Abstract: We study the formation process of an oxygen torus during the 12–15 November 2012 magnetic storm, using the magnetic field and plasma wave data obtained by Van Allen Probes. We estimate the local plasma mass density (ρL) and the local electron number density (neL) from the resonant frequencies of standing Alfvén waves and the upper hybrid resonance band. The average ion mass (M) can be calculated by M ∼ ρL/neL under the assumption of quasi-neutrality of plasma. During the storm recovery phase, both Probe A and Probe B observe the oxygen torus at L = 3.0–4.0 and L = 3.7–4.5, respectively, on the morning side. The oxygen torus has M = 4.5–8 amu and extends around the plasmapause that is identified at L∼3.2–3.9. We find that during the initial phase, M is 4–7 amu throughout . . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020593 Available at: http://doi.wiley.com/10.1002/2014JA020593
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Authors: Hwang K.-J., Sibeck D G, Fok M.-C. H., Zheng Y., Nishimura Y., et al.
Title: The global context of the 14 November, 2012 storm event
Abstract: From 2 to 5 UT on 14 November, 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ~20–30 min prior to. . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020826 Available at: http://doi.wiley.com/10.1002/2014JA020826
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Authors: Yu Xiongdong, Yuan Zhigang, Wang Dedong, Li Haimeng, Huang Shiyong, et al.
Title: In situ observations of EMIC waves in O + band by the Van Allen Probe A
Abstract: Through polarization and spectra analysis of the magnetic field observed by the Van Allen Probe A, we present two typical cases of O+ band EMIC waves in the outer plasmasphere or plasma trough. Although such O+ band EMIC waves are rarely observed, 18 different events of O+ band EMIC waves (16 events in the outer plasmasphere and 2 events in the plasma trough) are found from September 2012 to August 2014 with observations of the Van Allen Probe A. We find that the preferred region for the occurrence of O+ band EMIC waves is in L = 2-5 and MLT = 03-13, 19-20, which is in accordance with the occurrence region of O+ ion torus. Therefore, our result suggests that the O+ ion torus in the outer plasmasphere during geomagnetic activities should play an important role in the generation of EMIC wave. . .
Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL063250 Available at: http://doi.wiley.com/10.1002/2015GL063250
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Authors: Motoba T., Takahashi K., Ukhorskiy A., Gkioulidou M., Mitchell D G, et al.
Title: Link between pre-midnight second harmonic poloidal waves and auroral undulations: Conjugate observations with a Van Allen Probes spacecraft and a THEMIS all-sky imager
Abstract: We report, for the first time, an auroral undulation event on 1 May 2013 observed by an all-sky imager (ASI) at Athabasca (L = 4.6), Canada, for which in situ field and particle measurements in the conjugate magnetosphere were available from a Van Allen Probes spacecraft. The ASI observed a train of auroral undulation structures emerging spontaneously in the pre-midnight subauroral ionosphere, during the growth phase of a substorm. The undulations had an azimuthal wavelength of ~180 km and propagated westward at a speed of 3–4 km s−1. The successive passage over an observing point yielded quasi-periodic oscillations in diffuse auroral emissions with a period of ~40 s. The azimuthal wave number m of the auroral luminosity oscillations was found to be m ~ −103. During the event the spa. . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020863 Available at: http://doi.wiley.com/10.1002/2014JA020863
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Authors: Ma Q, Li W, Thorne R M, Ni B, Kletzing C A, et al.
Title: Modeling inward diffusion and slow decay of energetic electrons in the Earth's outer radiation belt
Abstract: A new 3D diffusion code is used to investigate the inward intrusion and slow decay of energetic radiation belt electrons (>0.5 MeV) observed by the Van Allen Probes during a 10-day quiet period in March 2013. During the inward transport the peak differential electron fluxes decreased by approximately an order of magnitude at various energies. Our 3D radiation belt simulation including radial diffusion and pitch angle and energy diffusion by plasmaspheric hiss and Electromagnetic Ion Cyclotron (EMIC) waves reproduces the essential features of the observed electron flux evolution. The decay timescales and the pitch angle distributions in our simulation are consistent with the Van Allen Probes observations over multiple energy channels. Our study suggests that the quiet-time energetic electro. . .
Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062977 Available at: http://doi.wiley.com/10.1002/2014GL062977
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Authors: Yu Yiqun, Jordanova Vania, Zou Shasha, Heelis Roderick, Ruohoniemi Mike, et al.
Title: Modeling sub-auroral polarization streams (SAPS) during the March 17, 2013 storm
Abstract: The sub-auroral polarization streams (SAPS) are one of the most important features in representing magnetosphere-ionosphere coupling processes. In this study, we use a state-of-the-art modeling framework that couples an inner magnetospheric ring current model RAM-SCB with a global MHD model BATS-R-US and an ionospheric potential solver to study the SAPS that occurred during the March 17, 2013 storm event as well as to assess the modeling capability. Both ionospheric and magnetospheric signatures associated with SAPS are analyzed to understand the spatial and temporal evolution of the electrodynamics in the mid-latitude regions. Results show that the model captures the SAPS at sub-auroral latitudes, where Region-2 field-aligned currents (FACs) flow down to the ionosphere and the conductance. . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020371 Available at: http://doi.wiley.com/10.1002/2014JA020371
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Authors: Zhu Hui, Su Zhenpeng, Xiao Fuliang, Zheng Huinan, Wang Yuming, et al.
Title: Plasmatrough exohiss waves observed by Van Allen Probes: Evidence for leakage from plasmasphere and resonant scattering of radiation belt electrons
Abstract: Exohiss waves are whistler mode hiss observed in the plasmatrough region. We present a case study of exohiss waves and the corresponding background plasma distributions observed by the Van Allen Probes in the dayside low-latitude region. The analysis of wave Poynting fluxes, suprathermal electron fluxes and cold electron densities supports the scenario that exohiss leaks from the plasmasphere into the plasmatrough. Quasilinear calculations further reveal that exohiss can potentially cause the resonant scattering loss of radiation belt electrons ~Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062964 Available at: http://doi.wiley.com/10.1002/2014GL062964
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Authors: Gkioulidou Matina, Ohtani S, Mitchell D G, Ukhorskiy A., Reeves G D, et al.
Title: Spatial structure and temporal evolution of energetic particle injections in the inner magnetosphere during the 14 July 2013 substorm event.
Abstract: Recent results by the Van Allen Probes mission showed that the occurrence of energetic ion injections inside geosynchronous orbit could be very frequent throughout the main phase of a geomagnetic storm. Understanding, therefore, the formation and evolution of energetic particle injections is critical in order to quantify their effect in the inner magnetosphere. We present a case study of a substorm event that occurred during a weak storm (Dst ~ - 40 nT) on 14 July 2013. Van Allen Probe B, inside geosynchronous orbit, observed two energetic proton injections within ten minutes, with different dipolarization signatures and duration. The first one is a dispersionless, short timescale injection pulse accompanied by a sharp dipolarization signature, while the second one is a dispersed, longer t. . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020872 Available at: http://doi.wiley.com/10.1002/2014JA020872
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Authors: O'Brien T.P., Claudepierre S.G., Looper M.D., Blake J.B., Fennell J.F., et al.
Title: On the use of drift echoes to characterize on-orbit sensor discrepancies
Abstract: We describe a method for using drift echo signatures in on-orbit data to resolve discrepancies between different measurements of particle flux. The drift period has a well-defined energy dependence, which gives rise to time dispersion of the echoes. The dispersion can then be used to determine the effective energy for one or more channels given each channel's drift period and the known energy for a reference channel. We demonstrate this technique on multiple instruments from the Van Allen probes mission. Drift echoes are only easily observed at high energies (100s keV to multiple MeV), where several drift periods occur before the observing satellite has moved on or the global magnetic conditions have changed. We describe a first-order correction for spacecraft motion. The drift echo techni. . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020859 Available at: http://doi.wiley.com/10.1002/2014JA020859
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Authors: Fennell J. F., Claudepierre S G, Blake J B, O'Brien T P, Clemmons J. H., et al.
Title: Van Allen Probes show the inner radiation zone contains no MeV electrons: ECT/MagEIS data
Abstract: We present Van Allen Probe observations of electrons in the inner radiation zone. The measurements were made by the ECT/MagEIS sensors that were designed to measure electrons with the ability to remove unwanted signals from penetrating protons, providing clean measurements. No electrons >900 keV were observed with equatorial fluxes above background (i.e. >0.1 electrons/(cm2 s sr keV)) in the inner zone. The observed fluxes are compared to the AE9 model and CRRES observations. Electron fluxes <200 keV exceeded the AE9 model 50% fluxes and were lower than the higher energy model fluxes. Phase space density radial profiles for 1.3≤L*<2.5 had mostly positive gradients except near L*~2.1 where the profiles for μ = 20-30 MeV/G were flat or slightly peaked. The major result is that MagEIS data. . .
Date: 02/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062874 Available at: http://doi.wiley.com/10.1002/2014GL062874
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Authors: Kurth W S, De Pascuale S., Faden J. B., Kletzing C A, Hospodarsky G B, et al.
Title: Electron Densities Inferred from Plasma Wave Spectra Obtained by the Waves Instrument on Van Allen Probes
Abstract: The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Fields Instrument Suite and Integrated Science (EMFISIS) suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves (EFW) triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency fuh. Considerable work has gone into developing . . .
Date: 01/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020857 Available at: http://doi.wiley.com/10.1002/2014JA020857
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Authors: Stephens G. K., Sitnov M I, Ukhorskiy A Y, Roelof E. C., Tsyganenko N A, et al.
Title: Empirical modeling of the storm-time innermost magnetosphere using Van Allen Probes and THEMIS data: Eastward and banana currents
Abstract: The structure of storm-time currents in the inner magnetosphere, including its innermost region inside 4RE, is studied for the first time using a modification of the empirical geomagnetic field model TS07D and new data from Van Allen Probes and THEMIS missions. It is shown that the model, which uses basis-function expansions instead of ad hoc current modules to approximate the magnetic field, consistently improves its resolution and magnetic field reconstruction with the increase of the number of basis functions and resolves the spatial structure and evolution of the innermost eastward current. This includes a connection between the westward ring current flowing largely at inline image and the eastward ring current concentrated at inline image resulting in a vortex current pattern. A simil. . .
Date: 01/2015 Publisher: Journal of Geophysical Research: Space Physics Pages: n/a - n/a DOI: 10.1002/2015JA021700 Available at: http://doi.wiley.com/10.1002/2015JA021700
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Authors: Foster J. C., Wygant J R, Hudson M K, Boyd A. J., Baker D N, et al.
Title: Shock-Induced Prompt Relativistic Electron Acceleration In the Inner Magnetosphere
Abstract: We present twin Van Allen Probes spacecraft observations of the effects of a solar wind shock impacting the magnetosphere on 8 October 2013. The event provides details both of the accelerating electric fields associated with the shock and the response of inner magnetosphere electron populations across a broad range of energies. During this period the two Van Allen Probes observed shock effects from the vantage point of the dayside magnetosphere at radial positions of L=3 and L=5, at the location where shock-induced acceleration of relativistic electrons occurs. The extended (~1 min) duration of the accelerating electric field across a broad extent of the dayside magnetosphere, coupled with energy dependent relativistic electron gradient drift velocities, selects a preferred range of energi. . .
Date: 01/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020642 Available at: http://doi.wiley.com/10.1002/2014JA020642
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Authors: Li X, Selesnick R. S., Baker D N, Jaynes A. N., Kanekal S G, et al.
Title: Upper limit on the inner radiation belt MeV electron Intensity
Abstract: No instruments in the inner radiation belt are immune from the unforgiving penetration of the highly energetic protons (10s of MeV to GeV). The inner belt proton flux level, however, is relatively stable, thus for any given instrument, the proton contamination often leads to a certain background noise. Measurements from the Relativistic Electron and Proton Telescope integrated little experiment (REPTile) on board Colorado Student Space Weather Experiment (CSSWE) CubeSat, in a low Earth orbit, clearly demonstrate that there exist sub-MeV electrons in the inner belt because of their flux level is orders of magnitude higher than the background, while higher energy electron (>1.6 MeV) measurements cannot be distinguished from the background. Detailed analysis of high-quality measurements from . . .
Date: 01/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020777 Available at: http://doi.wiley.com/10.1002/2014JA020777
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Authors: Korotova G. I., Sibeck D G, Tahakashi K., Dai L., Spence H E, et al.
Title: Van Allen Probe observations of drift-bounce resonances with Pc 4 pulsations and wave–particle interactions in the pre-midnight inner magnetosphere
Abstract: We present Van Allen Probe B observations of azimuthally limited, antisymmetric, poloidal Pc 4 electric and magnetic field pulsations in the pre-midnight sector of the magnetosphere from 05:40 to 06:00 UT on 1 May 2013. Oscillation periods were similar for the magnetic and electric fields and proton fluxes. The flux of energetic protons exhibited an energy-dependent response to the pulsations. Energetic proton variations were anticorrelated at medium and low energies. Although we attribute the pulsations to a drift-bounce resonance, we demonstrate that the energy-dependent response of the ion fluxes results from pulsation-associated velocities sweeping energy-dependent radial ion flux gradients back and forth past the spacecraft.
Date: 01/2015 Publisher: Annales Geophysicae Pages: 955 - 964 DOI: 10.5194/angeo-33-955-2015 Available at: http://www.ann-geophys.net/33/955/2015/angeo-33-955-2015.pdf
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2014
Authors: Jaynes A. N., Li X, Schiller Q. G., Blum L. W., Tu W., et al.
Title: Evolution of relativistic outer belt electrons during an extended quiescent period
Abstract: To effectively study steady loss due to hiss-driven precipitation of relativistic electrons in the outer radiation belt, it is useful to isolate this loss by studying a time of relatively quiet geomagnetic activity. We present a case of initial enhancement and slow, steady decay of 700 keV - 2 MeV electron populations in the outer radiation belt during an extended quiescent period from ~15 December 2012 - 13 January 2013. We incorporate particle measurements from a constellation of satellites, including the Colorado Student Space Weather Experiment (CSSWE) CubeSat, the Van Allen Probes twin spacecraft, and THEMIS, to understand the evolution of the electron populations across pitch angle and energy. Additional data from calculated phase space density (PSD), as well as hiss and chorus w. . .
Date: 12/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020125 Available at: http://doi.wiley.com/10.1002/2014JA020125
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Authors: Summers Danny, Omura Yoshiharu, Nakamura Satoko, and Kletzing Craig A.
Title: Fine structure of plasmaspheric hiss
Abstract: Plasmaspheric hiss has been widely regarded as a broadband, structureless, incoherent emission. In this study, by examining burst-mode vector waveform data from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument on the Van Allen Probes mission, we show that plasmaspheric hiss is a coherent emission with complex fine structure. Specifically, plasmaspheric hiss appears as discrete rising tone and falling tone elements. Our study comprises the analysis of two one-hour samples within which a total of 8 one-second samples were analyzed. By means of waveform analysis on two samples we identify typical amplitudes, phase profiles, and sweep rates of the rising and falling tone elements. The exciting new observations reported here can be expected to fuel a . . .
Date: 12/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020437 Available at: http://doi.wiley.com/10.1002/2014JA020437
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Authors: Li Zan, Millan Robyn M., Hudson Mary K, Woodger Leslie A., Smith David M., et al.
Title: Investigation of EMIC wave scattering as the cause for the BARREL January 17, 2013 relativistic electron precipitation event: a quantitative comparison of simulation with observations
Abstract: Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the BARREL balloons, and was magnetically mapped close to GOES-13. We simulate the relativistic electron pitch-angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES-13 and the Van Allen Probes. We show that the count rate, the energy distribution and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is . . .
Date: 12/2014 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062273 Available at: http://doi.wiley.com/10.1002/2014GL062273
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Authors: Su Zhenpeng, Zhu Hui, Xiao Fuliang, Zheng Huinan, Wang Yuming, et al.
Title: Quantifying the relative contributions of substorm injections and chorus waves to the rapid outward extension of electron radiation belt
Abstract: We study the rapid outward extension of the electron radiation belt on a timescale of several hours during three events observed by RBSP and THEMIS satellites, and particularly quantify the contributions of substorm injections and chorus waves to the electron flux enhancement near the outer boundary of radiation belt. A comprehensive analysis including both observations and simulations is performed for the first event on 26 May 2013. The outer boundary of electron radiation belt moved from L = 5.5 to L > 6.07 over about 6 hours, with up to four orders of magnitude enhancement in the 30 keV-5 MeV electron fluxes at L = 6. The observations show that the substorm injection can cause 100% and 20% of the total subrelativistic (~0.1 MeV) and relativistic (2-5 MeV) electron . . .
Date: 12/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020709 Available at: http://doi.wiley.com/10.1002/2014JA020709
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Authors: Betz Eric O.
Title: Trapping waves in Earth's plasmasphere
Abstract: Earth's magnetic field traps donut-shaped bands of radiation in a belt around the planet that react to solar eruptions by growing and shrinking. The Van Allen belts consist of two rings filled with particles from the solar wind and cosmic rays. Within the outer ring of the Van Allen belt sits the plasmasphere, which is the innermost part of the planet's magnetic field and home to low-energy charged particles.
Date: 12/2014 Publisher: Eos, Transactions American Geophysical Union Pages: 472 - 472 DOI: 10.1002/2014EO490016 Available at: http://doi.wiley.com/10.1002/eost.v95.49http://doi.wiley.com/10.1002/2014EO490016
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Authors: Boardsen S. A., Hospodarsky G B, Kletzing C A, Pfaff R. F., Kurth W S, et al.
Title: Van Allen Probe Observations of Periodic Rising Frequencies of the Fast Magnetosonic Mode
Abstract: Near simultaneous periodic dispersive features of fast magnetosonic mode emissions are observed by both Van Allen Probes spacecraft while separated in magnetic local time by ~5 hours: Probe A at 15 and Probe B at 9–11 hours. Both spacecraft see similar frequency features, characterized by a periodic repetition at ~180 s. Each repetition is characterized by a rising frequency. Since no modulation is observed in the proton shell distribution, the plasma density, or in the background magnetic field at either spacecraft we conclude that these waves are not generated near the spacecraft but external to both spacecraft locations. Probe A while outside the plasmapause sees the start of each repetition ~40 s before probe B while deep inside the plasmasphere. We can qualitatively reproduce . . .
Date: 12/2014 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL062020 Available at: http://doi.wiley.com/10.1002/2014GL062020
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Authors: Zhao H., Li X, Blake J B, Fennell J. F., Claudepierre S G, et al.
Title: Characteristics of pitch angle distributions of 100 s keV electrons in the slot region and inner radiation belt
Abstract: The pitch angle distribution (PAD) of energetic electrons in the slot region and inner radiation belt received little attention in the past decades due to the lack of quality measurements. Using the state-of-art pitch-angle-resolved data from the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard the Van Allen Probes, a detailed analysis of 100 s keV electron PADs below L = 4 is performed, in which the PADs is categorized into three types: normal (flux peaking at 90∘), cap (exceedingly peaking narrowly around 90∘) and 90∘-minimum (lower flux at 90∘) PADs. By examining the characteristics of the PADs of ~460 keV electrons for over a year, we find that the 90∘-minimum PADs are generally present in the inner belt (L < 2), while normal PADs dominate at .L ~3.5. . .
Date: 11/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020386 Available at: http://doi.wiley.com/10.1002/2014JA020386
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Authors: Mauk B H
Title: Comparative Investigation of the Energetic Ion Spectra Comprising the Magnetospheric Ring Currents of the Solar System
Abstract: Investigated here are factors that control the intensities and shapes of energetic ion spectra that make up the ring current populations of the strongly magnetized planets of the solar system, specifically those of Earth, Jupiter, Saturn, Uranus, and Neptune. Following a previous and similar comparative investigation of radiation belt electrons, we here turn our attention to ions. Specifically, we examine the possible role of the differential ion Kennel-Petschek limit, as moderated by Electromagnetic Ion Cyclotron (EMIC) waves, as a standard for comparing the most intense ion spectra within the strongly magnetized planetary magnetospheres. In carrying out this investigation, the substantial complexities engendered by the very different ion composition distributions of these diverse magneto. . .
Date: 11/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020392 Available at: http://doi.wiley.com/10.1002/2014JA020392
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Authors: Zhou Qinghua, Xiao Fuliang, Yang Chang, Liu Si, Kletzing C A, et al.
Title: Excitation of nightside magnetosonic waves observed by Van Allen Probes
Abstract: During the recovery phase of the geomagnetic storm on 30-31 March 2013, Van Allen Probe A detected enhanced magnetosonic (MS) waves in a broad range of L =1.8-4.7 and MLT =17-22 h, with a frequency range ~10-100 Hz. In the meanwhile, distinct proton ring distributions with peaks at energies of ~10 keV, were also observed in L =3.2-4.6 and L =5.0-5.6. Using a subtracted bi-Maxwellian distribution to model the observed proton ring distribution, we perform three dimensional ray tracing to investigate the instability, propagation and spatial distribution of MS waves. Numerical results show that nightside MS waves are produced by proton ring distribution and grow rapidly from the source location L =5.6 to the location L =5.0, but remain nearly stable at locations L <5.0 Moreover, waves launched. . .
Date: 11/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: n/a - n/a DOI: 10.1002/2014JA020481 Available at: http://doi.wiley.com/10.1002/2014JA020481
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Authors: Baker D N, Jaynes A. N., Hoxie V C, Thorne R M, Foster J. C., et al.
Title: An impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts
Abstract: Early observations1, 2 indicated that the Earth’s Van Allen radiation belts could be separated into an inner zone dominated by high-energy protons and an outer zone dominated by high-energy electrons. Subsequent studies3, 4 showed that electrons of moderate energy (less than about one megaelectronvolt) often populate both zones, with a deep ‘slot’ region largely devoid of particles between them. There is a region of dense cold plasma around the Earth known as the plasmasphere, the outer boundary of which is called the plasmapause. The two-belt radiation structure was explained as arising from strong electron interactions with plasmaspheric hiss just inside the plasmapause boundary5, with the inner edge of the outer radiation zone corresponding to the minimum plasmapause location6. Re. . .
Date: 11/2014 Publisher: Nature Pages: 531 - 534 DOI: 10.1038/nature13956 Available at: http://www.nature.com/doifinder/10.1038/nature13956
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Authors: Gerrard Andrew, Lanzerotti Louis, Gkioulidou Matina, Mitchell Donald, Manweiler Jerry, et al.
Title: Initial Measurements of O-ion and He-ion Decay Rates Observed from the Van Allen Probes RBSPICE Instrument
Abstract: H-ion (~45-keV to ~600-keV), He-ion (~65-keV to ~520-keV), and O-ion (~140-keV to ~1130-keV) integral flux measurements, from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft B, are reported. These abundance data form a cohesive picture of ring current ions during the first nine months of measurements. Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio. Of unique interest to ring current dynamics are the spatial-temporal decay characteristics of the two injected populations. We observe that He-ions decay more quickly at lower L-shells, on the orderof ~0.8-day at L-shells of 3–4, and decay more slowly with higher L-she. . .
Date: 11/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020374 Available at: http://doi.wiley.com/10.1002/2014JA020374
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Authors: Zanetti L. J., Mauk B H, Fox N.J., Barnes R.J., Weiss M, et al.
Title: The Evolving Space Weather System - Van Allen Probes Contribution
Abstract: The overarching goal and purpose of the study of space weather is clear - to understand and address the issues caused by solar disturbances on humans and technological systems. Space weather has evolved in the past few decades from a collection of concerned agencies and researchers to a critical function of the National Weather Service of NOAA. The general effects have also evolved from the well-known telegraph disruptions of the mid-1800’s to modern day disturbances of the electric power grid, communications and navigation, human spaceflight and spacecraft systems. The last two items in this list, and specifically the effects of penetrating radiation, were the impetus for the space weather broadcast implemented on NASA’s Van Allen Probes’ twin pair of satellites, launched in August . . .
Date: 10/2014 Publisher: Space Weather DOI: 10.1002/2014SW001108 Available at: http://doi.wiley.com/10.1002/2014SW001108
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Authors: Hao Y. X., Zong Q.-G., Wang Y. F., Zhou X.-Z., Zhang Hui, et al.
Title: Interactions of energetic electrons with ULF waves triggered by interplanetary shock: Van Allen Probes observations in the magnetotail
Abstract: We present in situ observations of a shock-induced substorm-like event on 13 April 2013 observed by the newly launched Van Allen twin probes. Substorm-like electron injections with energy of 30–500 keV were observed in the region from L∼5.2 to 5.5 immediately after the shock arrival (followed by energetic electron drift echoes). Meanwhile, the electron flux was clearly and strongly varying on the ULF wave time scale. It is found that both toroidal and poloidal mode ULF waves with a period of 150 s emerged following the magnetotail magnetic field reconfiguration after the interplanetary (IP) shock passage. The poloidal mode is more intense than the toroidal mode. The 90° phase shift between the poloidal mode Br and Ea suggests the standing poloidal waves in the Northern Hemisphere. F. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020023 Available at: http://doi.wiley.com/10.1002/2014JA020023
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Authors: Li Zhao, Hudson Mary, Jaynes Allison, Boyd Alexander, Malaspina David, et al.
Title: Modeling Gradual Diffusion Changes in Radiation Belt Electron Phase Space Density for the March 2013 Van Allen Probes Case Study
Abstract: March 2013 provided the first equinoctial period when all of the instruments on the Van Allen Probes spacecraft were fully operational. This interval was characterized by disturbances of outer zone electrons with two timescales of variation, diffusive and rapid dropout and restoration [Baker et al., 2014]. A radial diffusion model was applied to the month-long interval to confirm that electron phase space density is well described by radial diffusion for the whole month at low first invariant ≤400 MeV/G, but peaks in phase space density observed by the ECT instrument suite at higher first invariant are not reproduced by radial transport from a source at higher L. The model does well for much of the month-long interval, capturing three of four enhancements in phase space density which e. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020359 Available at: http://doi.wiley.com/10.1002/2014JA020359
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Authors: Fu Xiangrong, Cowee Misa M., Friedel Reinhard H., Funsten Herbert O, Gary Peter, et al.
Title: Whistler Anisotropy Instabilities as the Source of Banded Chorus: Van Allen Probes Observations and Particle-in-Cell Simulations
Abstract: Magnetospheric banded chorus is enhanced whistler waves with frequencies ωr < Ωe, where Ωe is the electron cyclotron frequency, and a characteristic spectral gap at ωr ≃ Ωe/2. This paper uses spacecraft observations and two-dimensional particle-in-cell (PIC) simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from HOPE instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron mod. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020364 Available at: http://doi.wiley.com/10.1002/2014JA020364
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Authors: Fok M.-C., Buzulukova N. Y., Chen S.-H., Glocer A., Nagai T., et al.
Title: The Comprehensive Inner Magnetosphere-Ionosphere Model
Abstract: Simulation studies of the Earth's radiation belts and ring current are very useful in understanding the acceleration, transport, and loss of energetic particles. Recently, the Comprehensive Ring Current Model (CRCM) and the Radiation Belt Environment (RBE) model were merged to form a Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model. CIMI solves for many essential quantities in the inner magnetosphere, including ion and electron distributions in the ring current and radiation belts, plasmaspheric density, Region 2 currents, convection potential, and precipitation in the ionosphere. It incorporates whistler mode chorus and hiss wave diffusion of energetic electrons in energy, pitch angle, and cross terms. CIMI thus represents a comprehensive model that considers the effects of the r. . .
Date: 09/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 7522 - 7540 DOI: 10.1002/jgra.v119.910.1002/2014JA020239 Available at: http://doi.wiley.com/10.1002/jgra.v119.9http://doi.wiley.com/10.1002/2014JA020239
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Authors: Wang X., Malaspina D. M., Hsu H.-W., Ergun R. E., and M. Horányi.
Title: The effects of magnetic fields on photoelectron-mediated spacecraft potential fluctuations
Abstract: Previously, we have experimentally studied photoelectron-mediated spacecraft potential fluctuations associated with time-dependent external electric fields. In this paper, we investigate the effects of magnetic fields on such spacecraft potential fluctuations. A magnetic field is created above the UV-illuminated surface of a spacecraft model to alter the escape rate of photoelectrons. The packet of the observed potential oscillations becomes less positive with increasing magnetic field strength because more of the emitted photoelectrons are returned to the surface. As a result, the photoelectric charging time is increased, corresponding to a decrease in the response frequency of the photoemitting surface. The amplitude of the potential oscillations decreases when the response frequency bec. . .
Date: 09/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 7319 - 7326 DOI: 10.1002/jgra.v119.910.1002/2014JA019923 Available at: http://doi.wiley.com/10.1002/jgra.v119.9http://doi.wiley.com/10.1002/2014JA019923
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Authors: Baker Daniel
Title: New Twists in Earth’s Radiation Belts
Abstract: In 1958, an early satellite, Explorer I, made the discovery that Earth is enshrouded in belts of extraordinarily high-energy, high-intensity radiation. Now called the Van Allen belts, after the researcher who led that satellite mission, these rings are known to wax and wane in intensity, for reasons that are still being investigated. Satellites now criss-cross these belts, so understanding what influences them has dire implications for communications and other technologies in our modern age. Solar storms and space weather can pump them up, making the radiation zones around Earth immensely more dangerous for days or even weeks on end. The author has been involved with instruments on the dual Radiation Belt Storm Probes satellites that were launched on August 30, 2012, into Earth orbit to st. . .
Date: 09/2014 Publisher: American Scientist Pages: 374 DOI: 10.1511/2014.110.374 Available at: http://www.americanscientist.org/issues/feature/2014/5/new-twists-in-earths-radiation-belts
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Authors: Gkioulidou Matina, Ukhorskiy A., Mitchell D G, Sotirelis T., Mauk B., et al.
Title: The role of small-scale ion injections in the buildup of Earth's ring current pressure: Van Allen Probes observations of the March 17 th , 2013 storm
Abstract: Energetic particle transport into the inner magnetosphere during geomagnetic storms is responsible for significant plasma pressure enhancement, which is the driver of large-scale currents that control the global electrodynamics within the magnetosphere-ionosphere system. Therefore, understanding the transport of plasma from the tail deep into the near-Earth magnetosphere, as well as the energization processes associated with this transport, is essential for a comprehensive knowledge of the near-Earth space environment. During the main phase of a geomagnetic storm on March 17th 2013 (minimum Dst ~ −137 nT), the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument on the Van Allen Probes observed frequent, small-scale proton injections deep into the inner nightsi. . .
Date: 09/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020096 Available at: http://doi.wiley.com/10.1002/2014JA020096
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Authors: Goldstein J, De Pascuale S., Kletzing C., Kurth W., Genestreti K. J., et al.
Title: Simulation of Van Allen Probes Plasmapause Encounters
Abstract: We use an E × B-driven plasmapause test particle (PTP) simulation to provide global contextual information for in situ measurements by the Van Allen Probes (RBSP) during 15–20 January 2013. During 120 h of simulation time beginning on 15 January, geomagnetic activity produced three plumes. The third and largest simulated plume formed during enhanced convection on 17 January, and survived as a rotating, wrapped, residual plume for tens of hours. To validate the simulation, we compare its output with RBSP data. Virtual RBSP satellites recorded 28 virtual plasmapause encounters during 15–19 January. For 26 of 28 (92%) virtual crossings, there were corresponding actual RBSP encounters with plasmapause density gradients. The mean difference in encounter time between model and data is. . .
Date: 09/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020252 Available at: http://doi.wiley.com/10.1002/2014JA020252
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Authors: Ma Q, Li W, Chen L, Thorne R M, Kletzing C A, et al.
Title: The trapping of equatorial magnetosonic waves in the Earth's outer plasmasphere
Abstract: We investigate the excitation and propagation of equatorial magnetosonic waves observed by the Van Allen Probes and describe evidence for a trapping mechanism for magnetosonic waves in the Earth's plasmasphere. Intense equatorial magnetosonic waves were observed inside the plasmasphere in association with a pronounced proton ring distribution, which provides free energy for wave excitation. Instability analysis along the inbound orbit demonstrates that broadband magnetosonic waves can be excited over a localized spatial region near the plasmapause. The waves can subsequently propagate into the inner plasmasphere and remain trapped over a limited radial extent, consistent with the predictions of near-perpendicular propagation. By performing a similar analysis on another observed magnetosoni. . .
Date: 09/2014 Publisher: Geophysical Research Letters Pages: 6307 - 6313 DOI: 10.1002/2014GL061414 Available at: http://doi.wiley.com/10.1002/2014GL061414
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Authors: Reeves G D, Spence H E, Henderson M G, Tu W., Cunningham G. S., et al.
Title: Acceleration and loss driven by VLF chorus: Van Allen Probes observations and DREAM model results
Abstract: For over a decade now we have understood the response of the Earth's radiation belts to solar wind driving are a delicate balance of acceleration and loss processes. Theory has shown that the interaction of relativistic electrons with VLF whistler mode chorus can produce both energization through momentum diffusion and loss through pitch angle diffusion. Recent results from the Van Allen Probes mission has confirmed observationally that chorus can produce both acceleration and loss. The Van Allen Probes satellites are able to measure all the critical particle populations and wave fields with unprecedented precision and resolution but only at the two spacecraft locations. Those spatially-localized observations can be extended globally using three-dimensional diffusion codes such as the DREA. . .
Date: 08/2014 Publisher: IEEE DOI: 10.1109/URSIGASS.2014.6929879 Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6929879
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Authors: Li W, Ni B, Thorne R M, Bortnik J, Green J C, et al.
Title: Calculation of whistler-mode wave intensity using energetic electron precipitation
Abstract: The energetic electron population measured by multiple low-altitude POES satellites is used to infer whistlermode wave amplitudes using a physics-based inversion technique. We validate this technique by quantitatively analyzing a conjunction event between the Van Allen Probes and POES, and find that the inferred hiss wave amplitudes from POES electron measurements agree remarkably well with directly measured hiss waves amplitudes. We also use this technique to construct the global distribution of chorus wave intensity with extensive coverage over a broad L-MLT region during the 8–9 October 2012 storm and demonstrate that the inferred chorus wave amplitudes agree well with conjugate measurements of chorus wave amplitudes from the Van Allen Probes. The evolution of the whistler-mode wave i. . .
Date: 08/2014 Publisher: IEEE DOI: 10.1109/URSIGASS.2014.6929965 Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6929965
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Authors: Su Zhenpeng, Xiao Fuliang, Zheng Huinan, and Zhu Hui
Title: Chorus-driven acceleration of radiation belt electrons in the unusual temporal/spatial regions
Abstract: Cyclotron resonance with whistler-mode chorus waves is an important mechanism for the local acceleration of radiation belt energetic electrons. Such acceleration process has been widely investigated during the storm times, and its favored region is usually considered to be the low-density plasmatrough with magnetic local time (MLT) from midnight through dawn to noon. Here we present two case studies on the chorus-driven acceleration of radiation belt electrons in some “unusual” temporal /spatial regions. (1) The first event recorded by the Van Allen Probes during the nonstorm times from 21 to 23 February 2013. Within two days, a new radiation belt centering around L=5.8 formed and gradually merged with the original outer belt. The corresponding relativistic electron fluxes increased by. . .
Date: 08/2014 Publisher: IEEE DOI: 10.1109/URSIGASS.2014.6929875 Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6929875
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Authors: Lui A. T. Y., Mitchell D G, and Lanzerotti L J
Title: Comparison of Energetic Electron Intensities Outside and Inside the Radiation Belts
Abstract: The intensities of energetic electrons (~25 – 800 keV) outside and inside Earth's radiation belts are reported using measurements from THEMIS and Van Allen Probes during non-geomagnetic storm periods. Three intervals of current disruption/dipolarization events in August, 2013 were selected for comparison. The following results are obtained. (1) Phase space densities (PSDs) for the equatorially mirroring electron population at three values of the first adiabatic invariant (20, 70, and 200 MeV/G) at the outer radiation belt boundary are found to be one to three orders of magnitude higher than values measured just inside the radiation belt. (2) There is indication that substorm activity leads to PSD increases inside L = 5.5 in less than 1 hr. (3) Evidence for progressive inward tr. . .
Date: 08/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020049 Available at: http://doi.wiley.com/10.1002/2014JA020049
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Authors: Thomas Evan G., Yan Jingye, Zhang Jiaojiao, Baker Joseph B. H., Ruohoniemi Michael, et al.
Title: An examination of the source of decameter-scale irregularities in the geomagnetically disturbed mid-latitude ionosphere
Abstract: We present first results from a study of the plasma instability mechanism responsible for the small-scale (∼10 m) ionospheric density irregularities commonly observed by the Super Dual Auroral Radar Network (SuperDARN) HF radars in the vicinity of Sub Auroral Polarization Streams (SAPS) during periods of geomagnetic disturbance. A focus is placed on the mid-latitude region of the ionosphere over North America where recent expansion of the SuperDARN network allows for extensive direct comparisons with total electron content (TEC) measurements from a dense network of ground-based GPS receivers. The TEC observations indicate that high-speed SAPS channels and the associated small-scale irregularities are typically located within the mid-latitude ionospheric trough. The Millstone Hill Incoher. . .
Date: 08/2014 Publisher: IEEE DOI: 10.1109/URSIGASS.2014.6929853 Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6929853
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Authors: Chen Lunjin, Thorne Richard M, Bortnik Jacob, Li Wen, Horne Richard B, et al.
Title: Generation of Unusually Low Frequency Plasmaspheric Hiss
Abstract: It has been reported from Van Allen Probe observations that plasmaspheric hiss intensification in the outer plasmasphere, associated with a substorm injection on Sept 30 2012, occurred with a peak frequency near 100 Hz, well below the typical plasmaspheric hiss frequency range, extending down to ~20 Hz. We examine this event of unusually low frequency plasmaspheric hiss to understand its generation mechanism. Quantitative analysis is performed by simulating wave ray paths via the HOTRAY ray tracing code with measured plasma density and calculating ray path-integrated wave gain evaluated using the measured energetic electron distribution. We demonstrate that the growth rate due to substorm injected electrons is positive but rather weak, leading to small wave gain (~10 dB) during a sin. . .
Date: 08/2014 Publisher: Geophysical Research Letters DOI: 10.1002/2014GL060628 Available at: http://doi.wiley.com/10.1002/2014GL060628
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