Bibliography
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Found 1109 entries in the Bibliography.
Showing entries from 801 through 850
| 2015 |
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On the use of drift echoes to characterize on-orbit sensor discrepancies 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\textquoterights 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 technique has provided a significant clue in resolving substantial flux discrepancies between two instruments measuring fluxes near 2 MeV. O\textquoterightBrien, T.P.; Claudepierre, S.G.; Looper, M.D.; Blake, J.B.; Fennell, J.F.; Clemmons, J.H.; Roeder, J.L.; Kanekal, S.G.; Manweiler, J.W.; Mitchell, D.G.; Gkioulidou, M.; Lanzerotti, L.J.; Spence, H.E.; Reeves, G.D.; Baker, D.N.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020859 |
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Van Allen Probes show the inner radiation zone contains no MeV electrons: ECT/MagEIS data 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 do not show the presence of significant fluxes of MeV electrons in the inner zone while current radiation belt models and previous publications do. Fennell, J.; Claudepierre, S.; Blake, J.; O\textquoterightBrien, T.; Clemmons, J.; Baker, D.; Spence, H.; Reeves, G.; Published by: Geophysical Research Letters Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014GL062874 inner magnetosphere; Inner radiation belt; Inner zone; trapped electrons; Van Allen Probes |
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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\textendash0.9 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 dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater 56\% of the time over the full chorus wave band, 60\% of the time for lower band chorus, and 59\% of the time for upper band chorus. Hence, during active periods, empirical chorus wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons. Hartley, D.; Chen, Y.; Kletzing, C.; Denton, M.; Kurth, W.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020808 chorus waves; EMFISIS; energetic electrons; Radiation belts; Van Allen Probes; wave-particle interactions |
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This paper introduces a hierarchical simulation and modeling framework that allows for inference and validation of the likelihood function in Bayesian inversion of vadose zone hydraulic properties. The likelihood function or its analogs (objective functions and likelihood measures) are commonly assumed to be multivariate Gaussian in form; however, this assumption is not possible to verify without a hierarchical simulation and modeling framework. In this paper, we present the necessary statistical mechanisms for utilizing the hierarchical framework. We apply the hierarchical framework to the inversion of the vadose zone hydraulic properties within a multilayer soil profile conditioned on moisture content observations collected in the uppermost four layers. The key result of our work is that the goodness-of-fit validated likelihood function form provides empirical justification for the assumption of multivariate Gaussian likelihood functions in past and future inversions at similar sites. As an alternative, the likelihood function need not be assumed to follow a parametric statistical distribution and can be computed directly using nonparametric methods. The nonparametric methods are considerably more computationally demanding, and to demonstrate this approach, we present a smaller dimension synthetic case study of evaporation from a soil column. The main drawback of our work is the increased computational expense of the inversion. Over, Matthew; Wollschläger, Ute; Osorio-Murillo, Carlos; Rubin, Yoram; Published by: Water Resources Research Published on: 02/2015 YEAR: 2015 DOI: 10.1002/wrcr.v51.210.1002/2014WR015252 likelihood function; model inversion; vadose zone; validation |
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Ecohydrologic role of solar radiation on landscape evolution Solar radiation has a clear signature on the spatial organization of ecohydrologic fluxes, vegetation patterns and dynamics, and landscape morphology in semiarid ecosystems. Existing landscape evolution models (LEMs) do not explicitly consider spatially explicit solar radiation as model forcing. Here, we improve an existing LEM to represent coupled processes of energy, water, and sediment balance for semiarid fluvial catchments. To ground model predictions, a study site is selected in central New Mexico where hillslope aspect has a marked influence on vegetation patterns and landscape morphology. Model predictions are corroborated using limited field observations in central NM and other locations with similar conditions. We design a set of comparative LEM simulations to investigate the role of spatially explicit solar radiation on landscape ecohydro-geomorphic development under different uplift scenarios. Aspect-control and network-control are identified as the two main drivers of soil moisture and vegetation organization on the landscape. Landscape-scale and long-term implications of these short-term ecohdrologic patterns emerged in modeled landscapes. As north facing slopes (NFS) get steeper by continuing uplift they support erosion-resistant denser vegetation cover which leads to further slope steepening until erosion and uplift attains a dynamic equilibrium. Conversely, on south facing slopes (SFS), as slopes grow with uplift, increased solar radiation exposure with slope supports sparser biomass and shallower slopes. At the landscape scale, these differential erosion processes lead to asymmetric development of catchment forms, consistent with regional observations. Understanding of ecohydrogeomorphic evolution will improve to assess the impacts of past and future climates on landscape response and morphology. Yetemen, Omer; Istanbulluoglu, Erkan; Flores-Cervantes, Homero; Vivoni, Enrique; Bras, Rafael; Published by: Water Resources Research Published on: 02/2015 YEAR: 2015 DOI: 10.1002/wrcr.v51.210.1002/2014WR016169 catchment evolution; ecohydrology; geomorphology; landscape evolution; solar radiation; vegetation dynamics |
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Energetic electron injections deep into the inner magnetosphere associated with substorm activity From a survey of the first nightside season of NASA\textquoterights Van Allen Probes mission (Dec/2012 \textendash 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 the Pi 2 frequency range inside the plasmasphere. These observations demonstrate that injections occur at very low L-shells and may play an important role for inner zone electrons. Turner, D.; Claudepierre, S.; Fennell, J.; O\textquoterightBrien, T.; Blake, J.; Lemon, C.; Gkioulidou, M.; Takahashi, K.; Reeves, G.; Thaller, S.; Breneman, A.; Wygant, J.; Li, W.; Runov, A.; Angelopoulos, V.; Published by: Geophysical Research Letters Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2015GL063225 energetic particle injections; inner magnetosphere; Radiation belts; substorms; THEMIS; Van Allen Probes |
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Field-aligned chorus wave spectral power in Earth\textquoterights outer radiation belt Chorus-type whistler waves are one of the most intense electromagnetic waves generated naturally in the magnetosphere. These waves have a substantial impact on the radiation belt dynamics as they are thought to contribute to electron acceleration and losses into the ionosphere through resonant wave\textendashparticle interaction. Our study is devoted to the determination of chorus wave power distribution on frequency in a wide range of magnetic latitudes, from 0 to 40\textdegree. We use 10 years of magnetic and electric field wave power measured by STAFF-SA onboard Cluster spacecraft to model the initial (equatorial) chorus wave spectral power, as well as PEACE and RAPID measurements to model the properties of energetic electrons (~ 0.1\textendash100 keV) in the outer radiation belt. The dependence of this distribution upon latitude obtained from Cluster STAFF-SA is then consistently reproduced along a certain L-shell range (4 <= L <= 6.5), employing WHAMP-based ray tracing simulations in hot plasma within a realistic inner magnetospheric model. We show here that, as latitude increases, the chorus peak frequency is globally shifted towards lower frequencies. Making use of our simulations, the peak frequency variations can be explained mostly in terms of wave damping and amplification, but also cross-L propagation. These results are in good agreement with previous studies of chorus wave spectral extent using data from different spacecraft (Cluster, POLAR and THEMIS). The chorus peak frequency variations are then employed to calculate the pitch angle and energy diffusion rates, resulting in more effective pitch angle electron scattering (electron lifetime is halved) but less effective acceleration. These peak frequency parameters can thus be used to improve the accuracy of diffusion coefficient calculations. Breuillard, H.; Agapitov, O.; Artemyev, A.; Kronberg, E.; Haaland, S.; Daly, P.; Krasnoselskikh, V.; Boscher, D.; Bourdarie, S.; Zaliznyak, Y.; Rolland, G.; Published by: Annales Geophysicae Published on: 01/2015 YEAR: 2015 DOI: 10.5194/angeo-33-583-2015 |
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Recent ray tracing suggests that plasmaspheric hiss can originate from chorus observed outside of the plasmapause. Although a few individual events have been reported to support this mechanism, the number of reported conjugate events is still very limited. Using coordinated observations between THEMIS and Van Allen Probes, we report on an interesting event, where chorus was observed at a large L-shell (~9.8), different from previously reported events at L < 6, but still exhibited a remarkable correlation with hiss observed in the outer plasmasphere (L ~ 5.5). Ray tracing indicates that a subset of chorus can propagate into the observed location of hiss on a timescale of ~ 5-6 s, in excellent agreement with the observed time lag between chorus and hiss. This provides quantitative support that chorus from large L-shells, where it was previously considered unable to propagate into the plasmasphere, can in fact be the source of hiss. Li, W.; Chen, L.; Bortnik, J.; Thorne, R.; Angelopoulos, V.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2014GL062832 |
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Modeling CME-shock driven storms in 2012 - 2013: MHD-test particle simulations The Van Allen Probes spacecraft have provided detailed observations of the energetic particles and fields environment for CME-shock driven storms in 2012 to 2013 which have now been modeled with MHD-test particle simulations. The Van Allen Probes orbital plane longitude moved from the dawn sector in 2012 to near midnight and pre-noon for equinoctial storms of 2013, providing particularly good measurements of the inductive electric field response to magnetopause compression for the 8 October 2013 CME-shock driven storm. An abrupt decrease in the outer boundary of outer zone electrons coincided with inward motion of the magnetopause for both 17 March and 8 October 2013 storms, as was the case for storms shortly after launch (Hudson et al., 2014). Modeling magnetopause dropout events in 2013 with electric field diagnostics that were not available for storms immediately following launch has improved our understanding of the complex role that ULF waves play in radial transport during such events. Hudson, M.; Paral, J.; Kress, B.; Wiltberger, M.; Baker, D.; Foster, J.; Turner, D.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2014JA020833 |
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Shock-Induced Prompt Relativistic Electron Acceleration In the Inner Magnetosphere 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 energies (3 \textendash 4 MeV) for the initial enhancement. Those electrons—whose drift velocity closely matches the azimuthal phase velocity of the shock-induced pulse— stayed in the accelerating wave as it propagated tailward and received the largest increase in energy. Drift resonance with subsequent strong ULF waves further accentuated this range of electron energies. Phase space density and positional considerations permit identification of the source population of the energized electrons. Observations detail the promptness (<20 min), energy range (1.5-4.5 MeV), energy increase (~500 keV), and spatial extent (L*~3.5-4.0) of the enhancement of the relativistic electrons. Prompt acceleration by impulsive shock-induced electric fields and subsequent ULF wave processes therefore comprises a significant mechanism for the acceleration of highly relativistic electrons deep inside the outer radiation belt as shown clearly by this event. Foster, J.; Wygant, J.; Hudson, M.; Boyd, A.; Baker, D.; Erickson, P.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2014JA020642 |
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Upper limit on the inner radiation belt MeV electron Intensity 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 the Relativistic Electron and Proton Telescope (REPT) on board Van Allen Probes, in a geo-transfer-like orbit, provides, for the first time, quantified upper limits on MeV electron fluxes in various energy ranges in the inner belt. These upper limits are rather different from flux levels in the AE8 and AE9 models, which were developed based on older data sources. For 1.7, 2.5, and 3.3 MeV electrons, the upper limits are about one order of magnitude lower than predicted model fluxes. The implication of this difference is profound in that unless there are extreme solar wind conditions, which have not happened yet since the launch of Van Allen Probes, significant enhancements of MeV electrons do not occur in the inner belt even though such enhancements are commonly seen in the outer belt. Li, X.; Selesnick, R.; Baker, D.; Jaynes, A.; Kanekal, S.; Schiller, Q.; Blum, L.; Fennell, J.; Blake, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2014JA020777 |
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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. Korotova, G.; Sibeck, D.; Tahakashi, K.; Dai, L.; Spence, H.; Kletzing, C.; Wygant, J.; Manweiler, J.; Moya, P.; Hwang, K.-J.; Redmon, R.; Published by: Annales Geophysicae Published on: 01/2015 YEAR: 2015 DOI: 10.5194/angeo-33-955-2015 |
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During 18 February to 2 March 2014, the Van Allen Probes encountered multiple geomagnetic storms and simultaneously observed intensified chorus and hiss waves. During this period, there were substantial enhancements in fluxes of energetic (53.8 - 108.3 keV) and relativistic (2 - 3.6 MeV) electrons. Chorus waves were excited at locations L = 4 - 6.2 after the fluxes of energetic were greatly enhanced, with a lower frequency band and wave amplitudes \~ 20 - 100 pT. Strong hiss waves occurred primarily in the main phases or below the location L = 4 in the recovery phases. Relativistic electron fluxes decreased in the main phases due to the adiabatic (e.g., the magnetopause shadowing) or non-adiabatic (hiss-induced scattering) processes. In the recovery phases, relativistic electron fluxes either increased in the presence of enhanced chorus, or remained unchanged in the absence of strong chorus or hiss. The observed relativistic electron phase space density peaked around L* = 4.5, characteristic of local acceleration. This multiple-storm period reveals a typical picture that chorus waves are excited by the energetic electrons at first and then produce efficient acceleration of relativistic electrons. This further demonstrates that the interplay between both competing mechanisms of chorus-driven acceleration and hiss-driven scattering often occurs in the outer radiation belts. Liu, Si; Xiao, Fuliang; Yang, Chang; He, Yihua; Zhou, Qinghua; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2014JA020781 |
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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 a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission, but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify fuh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify fuh and accurately determine ne. In some cases there is not a clear signature of the upper hybrid band and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum. Kurth, W.; De Pascuale, S.; Faden, J.; Kletzing, C.; Hospodarsky, G.; Thaller, S.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2014JA020857 |
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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 similar pattern coined \textquoteleftbanana current\textquoteright was previously inferred from the pressure distributions based on the energetic neutral atom imaging and first-principles ring current simulations. The morphology of the equatorial currents is dependent on storm phase. During the main phase, it is complex, with several asymmetries forming \textquoterightbanana currents\textquoteright. Near Sym-H minimum, the \textquoterightbanana current\textquoteright is strongest, is localized in the evening-midnight sector, and is more structured compared to the main phase. It then weakens during the recovery phase resulting in the equatorial currents to become mostly azimuthally symmetric. Stephens, G.; Sitnov, M.; Ukhorskiy, A; Roelof, E.; Tsyganenko, N.; Le, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2015 YEAR: 2015 DOI: 10.1002/2015JA021700 eastward current; empirical geomagnetic field; magnetic storm; ring current; Van Allen Probes |
| 2014 |
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Van Allen Probe Observations of Periodic Rising Frequencies of the Fast Magnetosonic Mode 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\textendash11 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 the dispersive features, but not the quantitative details. The cause for this phenomena remains to be identified. Boardsen, S.; Hospodarsky, G.; Kletzing, C.; Pfaff, R.; Kurth, W.; Wygant, J.; MacDonald, E.; Published by: Geophysical Research Letters Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014GL062020 Fast Magnetosonic Waves; Inner Dayside Magnetosphere; Periodic-Dispersive Features; Van Allen Probes |
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Wave normal angles of whistler-mode chorus rising and falling tones We present a study of wave normal angles (θk) of whistler mode chorus emission as observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) during the year 2008. The three inner THEMIS satellites THA, THD, and THE usually orbit Earth close to the dipole magnetic equator (\textpm20\textdegree), covering a large range of L shells from the plasmasphere out to the magnetopause. Waveform measurements of electric and magnetic fields enable a detailed polarization analysis of chorus below 4 kHz. When displayed in a frequency-θk histogram, four characteristic regions of occurrence are evident. They are separated by gaps at f/fc,e≈0.5 (f is the chorus frequency, fc,e is the local electron cyclotron frequency) and at θk\~40\textdegree. Below θk\~40\textdegree, the average value for θk is predominantly field aligned, but slightly increasing with frequency toward half of fc,e (θk up to 20\textdegree). Above half of fc,e, the average θk is again decreasing with frequency. Above θk\~40\textdegree, wave normal angles are usually close to the resonance cone angle. Furthermore, we present a detailed comparison of electric and magnetic fields of chorus rising and falling tones. Falling tones exhibit peaks in occurrence solely for θk>40\textdegree and are propagating close to the resonance cone angle. Nevertheless, when comparing rising tones to falling tones at θk>40\textdegree, the ratio of magnetic to electric field shows no significant differences. Thus, we conclude that falling tones are generated under similar conditions as rising tones, with common source regions close to the magnetic equatorial plane. Taubenschuss, Ulrich; Khotyaintsev, Yuri; ik, Ondrej; Vaivads, Andris; Cully, Christopher; Le Contel, Olivier; Angelopoulos, Vassilis; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020575 |
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Asymmetries in the magnetospheric magnetic field produce drift shell splitting, which causes the radial (drift shell) invariant to sometimes depend on pitch angle. Where drift shell splitting is significant, pitch angle scattering leads to diffusion in all three invariants of the particle\textquoterights motion, including cross diffusion. We examine the magnitude of drift shell splitting-related anomalous diffusion for outer zone electrons compared to conventional diffusion in the absence of drift shell splitting. We assume the primary local scattering process is wave-particle interactions with chorus. We find that anomalous radial diffusion can exceed that of conventional drift resonant radial diffusion for particles with energies near 0.1 MeV at all radial distances outside the plasmasphere during quiet to moderate geomagnetic activity and, it is significant at 0.5 MeV. Cross diffusion involving the radial invariant can exceed the geometric mean of the corresponding pure diffusion coefficients at 0.1 MeV, and that such cross diffusion is significant even at 0.5-1 MeV. At 1 MeV, cross diffusion is often significant. The highest radial distances and magnetic activity levels in our study do not always exhibit as much significant anomalous diffusion as moderate radial distances and activity levels. This can be explained by (a) stronger dependence of conventional diffusion on magnetic activity and radius, and (b) strongest drift shell splitting at moderate magnetic activity. Simulation codes that neglect the possibility for cross terms will likely systematically underperform, especially for 0.1-0.5 MeV electrons, for much of the outer zone for quiet to moderate levels of magnetic activity. Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020422 |
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Evolution of relativistic outer belt electrons during an extended quiescent period 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 wave data from Van Allen Probes, helps complete the picture of the slow precipitation loss of relativistic electrons during a quiet time. Electron loss to the atmosphere during this event is quantified through use of the Loss Index Method, utilizing CSSWE measurements at LEO. By comparing these results against equatorial Van Allen Probes electron flux data, we conclude the net precipitation loss of the outer radiation belt content to be greater than 92\%, suggesting no significant acceleration during this period, and resulting in faster electron loss rates than have previously been reported. Jaynes, A.; Li, X.; Schiller, Q.; Blum, L.; Tu, W.; Turner, D.; Ni, B.; Bortnik, J.; Baker, D.; Kanekal, S.; Blake, J.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020125 electron lifetime; hiss waves; pitch angle scattering; precipitation loss; Radiation belts; Van Allen Probes |
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Externally driven plasmaspheric ULF waves observed by the Van Allen Probes We analyze data acquired by the Van Allen Probes on 8 November 2012, during a period of extended low geomagnetic activity, to gain new insight into plasmaspheric ultra-low-frequency (ULF) waves. The waves exhibited strong spectral power in the 5\textendash40 mHzband and included multiharmonic toroidal waves visible up to the 11th harmonic, unprecedented in the plasmasphere. During this wave activity, the interplanetary magnetic field cone angle was small, suggesting that the waves were driven by broadband compressional ULF waves originating in the foreshock region. This source mechanism is supported by the tailward propagation of the compressional magnetic field perturbations at a phase velocity of a few hundred kilometers per second that is determined bythe cross phase analysis of data from the two spacecraft. We also find that the coherence and phase delay of the azimuthal components of the magnetic field from the two spacecraft strongly depend on the radial separation of the spacecraft and attribute this feature to field line resonance effects. Finally, using the observed toroidal wave frequencies, we estimate the plasma mass density for L = 2.6\textendash5.8. By comparing the mass density with the electron number density that is estimated from the spectrum of plasma waves, we infer that the plasma was dominated by H+ ions and was distributed uniformly along the magnetic field lines. The electron density is higher than the prediction of saturated plasmasphere models, and this \textquotedblleftsuper saturated\textquotedblright plasmasphere and the uniform ion distribution are consistent with the low geomagnetic activity that prevailed. Takahashi, Kazue; Denton, Richard; Kurth, William; Kletzing, Craig; Wygant, John; Bonnell, John; Dai, Lei; Min, Kyungguk; Smith, Charles; MacDowall, Robert; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020373 multispacecraft observation; Van Allen Probes; plasmasphere; ULF waves |
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Fine structure of plasmaspheric hiss 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 re-examination of the properties of plasmaspheric hiss, including a further re-analysis of the generation mechanism for hiss. Summers, Danny; Omura, Yoshiharu; Nakamura, Satoko; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020437 |
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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 the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date. Li, Zan; Millan, Robyn; Hudson, Mary; Woodger, Leslie; Smith, David; Chen, Yue; Friedel, Reiner; Rodriguez, Juan; Engebretson, Mark; Goldstein, Jerry; Fennell, Joseph; Spence, Harlan; Published by: Geophysical Research Letters Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014GL062273 BARREL; EMIC waves; GOES; pitch angle diffusion; RBSP; relativistic electron precipitation; Van Allen Probes |
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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 flux enhancements within a few minutes. The data-driven simulation supports that the strong chorus waves can yield 60\%-80\% of the total energetic (0.2-5.0 MeV) electron flux enhancement within about 6 hours. Some simple analyses are further given for the other two events on 2 and 29 June 2013, in which the contributions of substorm injections and chorus waves are shown to be qualitatively comparable to those for the first event. These results clearly illustrate the respective importance of substorm injections and chorus waves for the evolution of radiation belt electrons at different energies on a relatively short timescale. Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Zong, Q.-G.; He, Zhaoguo; Shen, Chao; Zhang, Min; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020709 Chorus wave; Electron acceleration; Radiation belt; substorm injection; Van Allen Probes; Wave-particle interaction |
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Bursty enhancements of hot electrons (≳0.5 keV) with duration of minutes sometimes occur in the tail magnetosheath. In this study we used the unique simultaneous measurements from the two Acceleration Reconnection Turbulence and Electrodynamics of Moon\textquoterights Interaction with the Sun probes to investigate the likely sources, spatial structures, and responsible processes for these hot electron enhancements. The enhancements can be seen at any distance across the magnetosheath, but those closer to the magnetopause are more often accompanied by magnetosheath density and flow magnitudes changing to more magnetosphere-like values. From simultaneous measurements with the two probes being on either side of magnetopause or both in the magnetosheath, it is evident that these hot electrons come from the magnetosphere near the current sheet without further energization and that the enhancements are a result of bursty lateral magnetosphere intrusion into the magnetosheath, the enhancements and changes in the magnetosheath properties becoming smaller with increasing outward distance from the intrusion. From limited events having specific separation distances and alignments between the probes, we estimated that a single isolated enhancement can have a thin and elongated structure as narrow as 2 RE wide in the X direction, as long as over 7 RE in the Y direction, and as thin as 1 RE in the Z direction. We propose that Kelvin\textendashHelmholtz perturbations at the magnetopause and subsequent magnetosphere-magnetosheath particle mixing due to reconnection or diffusion can plausibly play an important role in generating the bursty magnetosphere intrusion into the magnetosheath and the hot electron enhancements. Wang, Chih-Ping; Xing, Xiaoyan; Nakamura, T.; Lyons, Larry; Angelopoulos, Vassilis; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020603 |
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Trapping waves in Earth\textquoterights plasmasphere Earth\textquoterights 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\textquoterights magnetic field and home to low-energy charged particles. Published by: Eos, Transactions American Geophysical Union Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014EO490016 magnetosonic waves; Van Allen Probes; wave excitation; wave propagation |
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The distribution of trapped energetic electrons inside the Earth\textquoterights radiation belts is the focus of intense studies aiming at better describing the evolution of the space environment in the presence of various disturbances induced by the solar wind or by an enhanced lightning activity. Such studies are usually performed by means of comparisons with full numerical simulations solving the Fokker-Planck quasi-linear diffusion equation for the particle distribution function. Here, we present for the first time approximate but realistic analytical solutions for the electron distribution, which are shown to be in good agreement with exact numerical solutions in situations where resonant scattering of energetic electrons by whistler-mode hiss, lightning-generated or chorus waves, is the dominant process. Quiet-time distributions are well-recovered, as well as the evolution of energized relativistic electron distributions during disturbed geomagnetic conditions. It is further shown that careful comparisons between the analytical solutions and measured distributions may allow to infer important bounce and drift averaged wave characteristics (such as wave amplitude). It could also help to improve the global understanding of underlying physical phenomena. Mourenas, D.; Artemyev, A.; Agapitov, O.V.; Krasnoselskikh, V.; Li, W.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020443 electron distribution; pitch-angle distribution; Radiation belt |
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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 90o), cap (exceedingly peaking narrowly around 90o) and 90o-minimum (lower flux at 90o) PADs. By examining the characteristics of the PADs of ~460 keV electrons for over a year, we find that the 90o-minimum PADs are generally present in the inner belt (L < 2), while normal PADs dominate at .L ~3.5 - 4. In the region between, 90o-minimum PADs dominate during injection times and normal PADs dominate during quiet times. Cap PADs appear mostly at the decay phase of storms in the slot region and are likely caused by the pitch angle scattering of hiss waves. Fitting the normal PADs into sinnα form, the parameter n is much higher below L = 3 than that in the outer belt and relatively constant in the inner belt but changes significantly in the slot region (2 < L < 3) during injection times. As for the 90o-minimum PADs, by performing a detailed case study, we find in the slot region this type of PAD is likely caused by chorus wave heating, butthis mechanism can hardly explain the formation of 90o-minimum PADs at the center of inner belt. Zhao, H.; Li, X.; Blake, J.; Fennell, J.; Claudepierre, S.; Baker, D.; Jaynes, A.; Malaspina, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020386 energetic electrons; Inner radiation belt; Pitch angle distribution; plasmasphere; Slot region; Van Allen Probes; Wave-particle interaction |
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n this study we investigate the link between precipitating electrons from the Van Allen radiation belts and the dynamical plasmapause. We consider electron precipitation observations from the Polar Orbiting Environmental Satellite (POES) constellation during geomagnetic storms. Superposed epoch analysis is performed on precipitating electron observations for the 13 year period of 1999 to 2012 in two magnetic local time (MLT) sectors, morning and afternoon. We assume that the precipitation is due to wave-particle interactions and our two MLT sectors focus on chorus (outside the plasmapause) and plasmaspheric hiss (inside the plasmapause) waves. We generate simple expressions based on the geomagnetic index, Dst, which reproduce the chorus-driven observations for the >30 keV precipitating electron flux magnitudes. Additionally, we find expressions for the fitted spectral index to describe the flux variation with energy, allowing a full energy reproduction as a function of distance from the plasmapause. The hiss-driven precipitating flux occurs inside the plasmapause but is independent of distance from the plasmapause. In the POES observations the hiss-induced electron precipitation is only detectable above the instrument noise in the >300 keV and P6 (>800 keV) channels of the flux detection instrument. We have derived expressions for the storm time variation in flux inside the plasmapause using Dst as a proxy. The observations show that there is little evidence for >800 keV electron precipitation occurring outside of the plasmapause, in the MLT sectors studied. Whittaker, Ian; Clilverd, Mark; Rodger, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020446 |
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Characterization of the energy-dependent response of riometer absorption Ground based riometers provide an inexpensive means to continuously remote sense the precipitation of electrons in the dynamic auroral region of Earth\textquoterights ionosphere. The energy-dependent relationship between riometer absorption and precipitating electrons is thus of great importance for understanding the loss of electrons from the Earth\textquoterights magnetosphere. In this study, statistical and event-based analyses are applied to determine the energy of electrons to which riometers chiefly respond. Time-lagged correlation analysis of trapped to precipitating fluxes shows that daily averaged absorption best correlates with ~ 60 keV trapped electron flux at zero-time lag, although large variability is observed across different phases of the solar cycle. High-time resolution statistical cross-correlation analysis between signatures observed by riometer stations, and assuming electron motion due to gradient and curvature drift, results in inferred energies of 10-100 keV, with a clear maximum in occurrence for 40-60 keV electrons. One event is considered in detail utilizing riometer absorption signatures obtained from several stations. The mean inferred energies for the initial rise time and peak of the absorption after correction for electric field effects were ~70 keV, and ~60 keV, respectively. The analyses presented provide a means to characterize the energy of electrons to which riometers are responding in both a statistical sense, and during the evolution of individual events. Kellerman, A.; Shprits, Y; Makarevich, R.; Spanswick, E.; Donovan, E.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020027 cosmic noise absorption; electron energy; particle modeling; Radiation belts; riometer; electron precipitation |
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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 magnetospheres must be addressed, given that the dispersion properties of the EMIC waves are strongly determined by the ion composition of the plasmas within which the waves propagate. Chosen for comparison are the ion spectra within these systems that are the most intense observed, specifically at 100 keV and 1 MeV. We find that Earth and Jupiter are unique in having their most intense ion spectra likely limited and sculpted by the Kennel-Petschek process. The ion spectra of Saturn, Uranus, and Neptune reside far below their respective limits and are likely limited by interactions with gas and dust (Saturn) and by the absence of robust ion acceleration processes (Uranus and Neptune). Suggestions are provided for further testing the efficacy of the differential Kennel-Petschek limit for ions using the Van Allen Probes. Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020392 Ion Spectra; Magnetic Storms; Planetary magnetospheres; ring current; Van Allen Probes |
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Electron lifetimes from narrowband wave-particle interactions within the plasmasphere This paper is devoted to the systematic study of electron lifetimes from narrowband wave-particle interactions within the plasmasphere. It relies on a new formulation of the bounce-averaged quasi-linear pitch angle diffusion coefficients parameterized by a single frequency, ω, and wave normal angle, θ. We first show that the diffusion coefficients scale with ω/Ωce, where Ωce is the equatorial electron gyrofrequency, and that maximal pitch angle diffusion occurs along the line α0 = π/2\textendashθ, where α0 is the equatorial pitch angle. Lifetimes are computed for L shell values in the range [1.5, 3.5] and energies, E, in the range [0.1, 6] MeV as a function of frequency and wave normal angle. The maximal pitch angle associated with a given lifetime is also given, revealing the frequencies that are able to scatter nearly equatorial pitch angle particles. The lifetimes are relatively independent of frequency and wave normal angle after taking into consideration the scaling law, with a weak dependence on wave normal angle up to 60\textendash70\textdegree, increasing to infinity as the wave normal angle approaches the resonance cone. We identify regions in the (L, E) plane in which a single wave type (hiss, VLF transmitters, or lightning-generated waves) is dominant relative to the others. We find that VLF waves dominate the lifetime for 0.2\textendash0.4 MeV at L ~ 2 and for 0.5\textendash0.8 MeV at L ~ 1.5, while hiss dominates the lifetime for 2\textendash3 MeV at L = 3\textendash3.5. The influence of lightning-generated waves is always mixed with the other two and cannot be easily differentiated. Limitations of the method for addressing effects due to restricted latitude or pitch angle domains are also discussed. Finally, for each (L, E) we search for the minimum lifetime and find that the optimal frequency that produces this lifetime increases as L diminishes. Restricting the search to very oblique waves, which could be emitted during the Demonstration and Science Experiments satellite mission, we find that the optimal frequency is always close to 0.16Ωce. Ripoll, J.-F.; Albert, J.; Cunningham, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020217 DSX; electron; narrowband; plasmasphere; wave-particle interactions |
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Electron losses from the radiation belts caused by EMIC waves Electromagnetic Ion Cyclotron (EMIC) waves cause electron loss in the radiation belts by resonating with high-energy electrons at energies greater than about 500 keV. However, their effectiveness has not been fully quantified. Here we determine the effectiveness of EMIC waves by using wave data from the fluxgate magnetometer on CRRES to calculate bounce-averaged pitch angle and energy diffusion rates for L*=3.5\textendash7 for five levels of Kp between 12 and 18 MLT. To determine the electron loss, EMIC diffusion rates were included in the British Antarctic Survey Radiation Belt Model together with whistler mode chorus, plasmaspheric hiss, and radial diffusion. By simulating a 100 day period in 1990, we show that EMIC waves caused a significant reduction in the electron flux for energies greater than 2 MeV but only for pitch angles lower than about 60\textdegree. The simulations show that the distribution of electrons left behind in space looks like a pancake distribution. Since EMIC waves cannot remove electrons at all pitch angles even at 30 MeV, our results suggest that EMIC waves are unlikely to set an upper limit on the energy of the flux of radiation belt electrons. Kersten, Tobias; Horne, Richard; Glauert, Sarah; Meredith, Nigel; Fraser, Brian; Grew, Russell; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020366 |
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Excitation of nightside magnetosonic waves observed by Van Allen Probes 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 toward lower L-shells with different initial azimuthal angles propagate across different MLT regions with divergent paths at first, then gradually turn back toward higher L-shells and propagate across different MLT regions with convergent paths. The current results further reveal that MS waves are generated by a ring distribution of ~10 keV proton and proton ring in one region can contribute to the MS wave power in another region. Zhou, Qinghua; Xiao, Fuliang; Yang, Chang; Liu, Si; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020481 magnetosonic wave; RBSP results; Van Allen Probes; Wave-particle interaction |
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Feasibility study of astronaut standardized career dose limits in LEO and the outlook for BLEO Cosmic Study Group SG 3.19/1.10 was established in February 2013 under the aegis of the International Academy of Astronautics to consider and compare the dose limits adopted by various space agencies for astronauts in Low Earth Orbit. A preliminary definition of the limits that might later be adopted by crews exploring Beyond Low Earth Orbit was, in addition, to be made. The present paper presents preliminary results of the study reported at a Symposium held in Turin by the Academy in July 2013. First, an account is provided of exposure limits assigned by various partner space agencies to those of their astronauts that work aboard the International Space Station. Then, gaps in the scientific and technical information required to safely implement human missions beyond the shielding provided by the geomagnetic field (to the Moon, Mars and beyond) are identified. Among many recommendations for actions to mitigate the health risks potentially posed to personnel Beyond Low Earth Orbit is the development of a preliminary concept for a Human Space Awareness System to: provide for crewed missions the means of prompt onboard detection of the ambient arrival of hazardous particles; develop a strategy for the implementation of onboard responses to hazardous radiation levels; support modeling/model validation that would enable reliable predictions to be made of the arrival of hazardous radiation at a distant spacecraft; provide for the timely transmission of particle alerts to a distant crewed vehicle at an emergency frequency using suitably located support spacecraft. Implementation of the various recommendations of the study can be realized based on a two pronged strategy whereby Space Agencies/Space Companies/Private Entrepreneurial Organizations etc. address the mastering of required key technologies (e.g. fast transportation; customized spacecraft design) while the International Academy of Astronautics, in a role of handling global international co-operation, organizes complementary studies aimed at harnessing the strengths and facilities of emerging nations in investigating/solving related problems (e.g. advanced space radiation modeling/model validation; predicting the arrivals of Solar Energetic Particles and shocks at a distant spacecraft). Ongoing progress in pursuing these complementary parallel programs could be jointly reviewed bi-annually by the Space Agencies and the International Academy of Astronautics so as to maintain momentum and direction in globally progressing towards feasible human exploration of interplanetary space. Published by: Acta Astronautica Published on: 11/2014 YEAR: 2014 DOI: 10.1016/j.actaastro.2014.07.011 Dose limits; Galactic Cosmic Radiation; Solar Energetic Particles |
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First observation of rising-tone magnetosonic waves Magnetosonic (MS) waves are linearly polarized emissions confined near the magnetic equator with wave normal angle near 90\textdegree and frequency below the lower hybrid frequency. Such waves, also termed equatorial noise, were traditionally known to be \textquotedbllefttemporally continuous\textquotedblright in their time-frequency spectrogram. Here we show for the first time that MS waves actually have discrete wave elements with rising-tone features in their spectrogram. The frequency sweep rate of MS waves, ~1 Hz/s, is between that of chorus and electromagnetic ion cyclotron (EMIC) waves. For the two events we analyzed, MS waves occur outside the plasmapause and cannot penetrate into the plasmasphere; their power is smaller than that of chorus. We suggest that the rising-tone feature of MS waves is a consequence of nonlinear wave-particle interaction, as is the case with chorus and EMIC waves. Fu, H.; Cao, J.; Zhima, Z.; Khotyaintsev, Y.; Angelopoulos, V.; ik, O.; Omura, Y.; Taubenschuss, U.; Chen, L.; Huang, S; Published by: Geophysical Research Letters Published on: 11/2014 YEAR: 2014 DOI: 10.1002/grl.v41.2110.1002/2014GL061867 discrete; frequency sweep rate; magnetosonic wave; nonlinear wave-particle interaction; Plasmapause; rising tone |
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An impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts Early observations1, 2 indicated that the Earth\textquoterights 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 \textquoteleftslot\textquoteright 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. Recent observations have revealed unexpected radiation belt morphology7, 8, especially at ultrarelativistic kinetic energies9, 10 (more than five megaelectronvolts). Here we analyse an extended data set that reveals an exceedingly sharp inner boundary for the ultrarelativistic electrons. Additional, concurrently measured data11 reveal that this barrier to inward electron radial transport does not arise because of a physical boundary within the Earth\textquoterights intrinsic magnetic field, and that inward radial diffusion is unlikely to be inhibited by scattering by electromagnetic transmitter wave fields. Rather, we suggest that exceptionally slow natural inward radial diffusion combined with weak, but persistent, wave\textendashparticle pitch angle scattering deep inside the Earth\textquoterights plasmasphere can combine to create an almost impenetrable barrier through which the most energetic Van Allen belt electrons cannot migrate. Baker, D.; Jaynes, A.; Hoxie, V.; Thorne, R.; Foster, J.; Li, X.; Fennell, J.; Wygant, J.; Kanekal, S.; Erickson, P.; Kurth, W.; Li, W.; Ma, Q.; Schiller, Q.; Blum, L.; Malaspina, D.; Gerrard, A.; Lanzerotti, L.; Published by: Nature Published on: 11/2014 YEAR: 2014 DOI: 10.1038/nature13956 Magnetospheric physics; ultrarelativistic electrons; Van Allen Belts; Van Allen Probes |
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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\textendash4, and decay more slowly with higher L-shell, on the order of ~1.7-days at L-shells of 5\textendash6. Conversely, O-ions decay very rapidly (~1.5-hours) across all L-shells. The He-ion decay time are consistent with previously measured and calculated lifetimes associated with charge exchange. The O-ion decay time is much faster than predicted and is attributed to the inclusion of higher energy (>500-keV) O-ions in our decay rate estimation. We note that these measurements demonstrate a compelling need for calculation of high energy O-ion loss rates, which have not been adequately studied in the literature to date. Gerrard, Andrew; Lanzerotti, Louis; Gkioulidou, Matina; Mitchell, Donald; Manweiler, Jerry; Bortnik, Jacob; Keika, Kunihiro; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020374 inner magnetosphere; ion decay rates; Spacecraft measurements; Van Allen Probes |
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On long decays of electrons in the vicinity of the slot region observed by HEO3 Long decay periods of electron counts, which follow abrupt rises and last from weeks to months, have been observed by the HEO3 spacecraft in the vicinity of the slot region between the years 1998 and 2007. During the most stable decay periods as selected, e-folding timescales are extracted and statistically analyzed from observations as a function of L-shell and electron energy. A challenge is to reproduce the observed timescales from simulations of pitch angle diffusion by three acting waves\textendashthe plasmaspheric hiss, lightning-generated whistlers, and VLF transmitter waves. We perform full numerical simulations to accurately compute electron lifetimes. We choose to use the method and wave parameters proposed by Abel \& Thorne [1998] with the goal to assess whether they can reproduce lifetimes extracted from HEO observations. We show how hiss dominantly affect high energy electrons (E > 2 MeV) for L in [2, 3.5] and VLF transmitter waves control residency times of low energy electrons (<0.4 MeV) around L = 2. These interactions induce characteristic shapes of the lifetime profiles that will be discussed. We show how the wave amplitudes can be adjusted for the particular energy particles that are dominantly affected by one wave type only. Using these amplitudes, mean HEO lifetimes are reproduced within a factor 2 to 5. VLF occurrence rates and hiss amplitude turn out significantly higher than those proposed by Abel \& Thorne [1998]. The wide energy response of the sensors complicates the analysis because it blurs the electron lifetime dependence on energy, increases the overall lifetimes and reduces the differences between the different channel lifetimes. In particular, our simulations suggest the flux measured by an integrated energy sensor aboard HEO has a variable slope, i.e. a variable lifetime, during 10-20 days in our data, due to the faster decay of the low residency time particles while slower decaying particles control the steady decay. It can explain some of the multi-slopes decays observed by HEO. HEO electron long decay timescales are also compared to the timescales previously observed from SAMPEX and CRRES with differences attributed to factors such as instrument characteristic and different satellite orbits. Ripoll, J.-F.; Chen, Y.; Fennell, J.; Friedel, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020449 |
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Following the conclusion of the 2014 Space Weather Week in Boulder, Colorado, the NOAA National Geophysical Data Center and Space Weather Prediction Center cohosted a 1 day workshop on the intercalibration of solar energetic particle (SEP) measurements. The overall purpose of this workshop was to discuss the intercalibration of SEP measurements from different instruments and different spacecraft, to foster new cooperative intercalibration efforts, and to identify a path forward for establishing a set of intercalibration guidelines. The detailed objectives of this workshop were described by Rodriguez and Onsager [2014]. Ten talks were given at the workshop (available at ftp://ftp.ngdc.noaa.gov/STP/publications/spe_intercal/), interspersed with extensive discussions. One outcome of these discussions is a recommendation that a set of guidelines be drafted for the on-orbit cross comparison of solar energetic particle measurements, similar to the first optical calibration guidelines developed for the Global Space-based Inter-Calibration System (GSICS) of the World Meteorological Organization (WMO) and the Coordination Group for Meteorological Satellites [Datla et al., 2009]. Rodriguez, Juan; Onsager, Terrance; Heynderickx, Daniel; Jiggens, Piers; Published by: Space Weather Published on: 11/2014 YEAR: 2014 DOI: 10.1002/swe.v12.1110.1002/2014SW001134 cross calibration; interoperability; Solar Energetic Particles |
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We investigate the magnetospheric MHD and energetic electron response to a Storm Sudden Commencement (SSC) and subsequent magnetopause buffeting, focusing on an interval following an SSC event on 25 November 2001. We find that the electron flux signatures observed by LANL, Cluster, and GOES spacecraft during this event can largely be reproduced using an advective kinetic model for electron phase space density, using externally prescribed electromagnetic field inputs, (herein described as a \textquotedbllefttest-kinetic model\textquotedblright) with electromagnetic field inputs provided by a 2-D linear ideal MHD model for ULF waves. In particular, we find modulations in electron flux phase shifted by 90\textdegree from the local azimuthal ULF wave electric field (Eφ) and a net enhancement in electron flux after 1.5 h for energies between 500 keV and 1.5 MeV near geosynchronous orbit. We also demonstrate that electrons in this energy range satisfy the drift resonance condition for the ULF waves produced by the MHD model. This confirms the conclusions reached by Tan et al. (2011), that the energization process in this case is dominated by drift-resonant interactions between electrons and MHD fast mode waves, produced by fluctuations in solar wind dynamic pressure. Degeling, A.; Rankin, R.; Zong, Q.-G.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2013JA019672 adiabatic electron transport; magnetopause buffeting; Radiation belts; ULF waves |
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Electromagnetic ion cyclotron (EMIC) wave generation and propagation in Earth\textquoterights magnetosphere depend on readily measurable hot (a few to tens of keV) plasma sheet ions, elusive plasmaspheric or ionospheric cold (sub-eV to a few eV) ions, and partially heated warm ions (tens to hundreds of eV). Previous work has assumed all low-energy ions are cold and not considered possible effects of warm ions. Using measurements by multiple Time History of Events and Macroscale Interactions during Substorms spacecraft, we analyze four typical EMIC wave events in the four magnetic local time sectors and consider the properties of both cold and warm ions supplied from previous statistical studies to interpret the wave observations using linear theory. As expected, we find that dusk EMIC waves grow due to the presence of drifting hot anisotropic protons and cold plasmaspheric ions with a dominant cold proton component. Near midnight, EMIC waves are less common because warm heavy ions that suppress wave growth are more abundant there. The waves can grow when cold, plume-like density enhancements are present, however. Dawn EMIC waves, known for their peculiar properties, are generated away from the equator and change polarization during propagation through the warm plasma cloak. Noon EMIC waves can also be generated nonlocally and their properties modified during propagation by a plasmaspheric plume combined with low-energy ions from solar and terrestrial sources. Accounting for multiple ion species, measured wave dispersion, and propagation characteristics can explain previously elusive EMIC wave properties and are therefore important for future studies of EMIC wave effects on energetic particle depletion. Lee, Justin; Angelopoulos, Vassilis; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020469 EMIC waves; ion composition; ion cyclotron waves; low-energy ions; THEMIS; warm plasma effects |
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Radial diffusion simulations of the 20 September 2007 radiation belt dropout This is a study of a dropout of radiation belt electrons, associated with an isolated solar wind density pulse on 20 September 2007, as seen by the solid-state telescopes (SST) detectors on THEMIS (Time History of Events and Macroscale Interactions during Substorms). Omnidirectional fluxes were converted to phase space density at constant invariants M = 700 MeV G-1 and K = 0.014 RE G1/2, with the assumption of local pitch angle α ≈ 80\textdegree and using the T04 magnetic field model. The last closed drift shell, which was calculated throughout the time interval, never came within the simulation outer boundary of L* = 6. It is found, using several different models for diffusion rates, that radial diffusion alone only allows the data-driven, time-dependent boundary values at Lmax = 6 and Lmin = 3.7 to propagate a few tenths of an RE during the simulation; far too slow to account for the dropout observed over the broad range of L* = 4\textendash5.5. Pitch angle diffusion via resonant interactions with several types of waves (chorus, electromagnetic ion cyclotron waves, and plasmaspheric and plume hiss) also seems problematic, for several reasons which are discussed. Published by: Annales Geophysicae Published on: 11/2014 YEAR: 2014 DOI: 10.5194/angeo-32-925-2014 |
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The bandwidths and coherence coefficients of lower band whistler mode waves are analyzed using Time History of Events and Macroscale Interactions during Substorms (THEMIS) waveform data for rising tones, falling tones, and hiss-like emissions separately. We also evaluate their dependences on the spatial location, electron density, the ratio of plasma frequency to local electron gyrofrequency (fpe/fce), and the wave amplitude. Our results show that the bandwidth normalized by the local electron gyrofrequency (fce) of rising and falling tones is very narrow (~0.01 fce), smaller than that of the hiss-like emissions (~0.025 fce). Meanwhile, the normalized bandwidth of discrete emissions gradually decreases with increasing wave amplitude, whereas that of hiss-like emissions increases slowly. The coherence coefficient of rising and falling tones is extremely large (~1), while the coherence coefficient of hiss-like emissions is smaller but is still larger than 0.5. For all categories of whistler mode waves, the normalized bandwidth increases at larger L shells. Furthermore, the normalized bandwidth is positively correlated with local fpe/fce but is inversely correlated with the electron density. Interactions between radiation belt electrons and whistler mode waves have been widely described by quasi-linear diffusion theory. Our results suggest that although quasi-linear theory is not entirely applicable for modeling electron interactions with rising and falling tones due to their narrow bandwidth and high coherence coefficient, it is suitable to treat wave-particle interactions between electrons and low-amplitude hiss-like emissions. Moreover, the correlations between the normalized bandwidth of chorus waves (especially the discrete emissions) and other parameters may provide insights for the generation mechanism of chorus waves. Gao, X.; Li, W.; Thorne, R.; Bortnik, J.; Angelopoulos, V.; Lu, Q.; Tao, X.; Wang, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020158 bandwidth; coherence coefficient; nonlinear; quasi-linear; THEMIS; whistler mode waves |
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A ULF wave driver of ring current energization ULF wave radial diffusion plays an important role in the transport of energetic electrons in the outer radiation belt, yet similar ring current transport is seldom considered even though ions satisfy a nearly identical drift resonance condition albeit without the relativistic correction. By examining the correlation between ULF wave power and the response of the ring current, characterized by Dst, we demonstrate a definite correlation between ULF wave power and Dst. Significantly, the lagged correlation peaks such that ULF waves precede the response of the ring current and Dst. We suggest that this correlation is the result of enhanced radial transport and energization of ring current ions through drift resonance and ULF wave radial diffusion of ring current ions. An analysis and comparison of the ion and electron diffusion coefficients further support this conclusion, ULF waves providing an important missing physical transport process explaining Dst underestimation in ring current models. Murphy, Kyle; Mann, Ian; Ozeke, Louis; Published by: Geophysical Research Letters Published on: 10/2014 YEAR: 2014 DOI: 10.1002/grl.v41.1910.1002/2014GL061253 Dst; radial diffusion; ring current dynamics; ULF waves; wave particle interactions |
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An unusual long-lived relativistic electron enhancement event excited by sequential CMEs An unusual long-lived intense relativistic electron enhancement event from July to August 2004 is examined using data from Fengyun-1, POES, GOES, ACE, the Cluster Mission and geomagnetic indices. During the initial 6 days of this event, the observed fluxes in the outer zone enhanced continuously and their maximum increased from 2.1 \texttimes 102 cm-2\textperiodcenteredsr-1\textperiodcentereds-1 to 3.5 \texttimes 104 cm-2\textperiodcenteredsr-1\textperiodcentereds-1, the region of enhanced fluxes extended from L = 3.5-6.5 to L = 2.5-6.5, and the flux peak location shifted inward from L ~ 4.2 to L ~ 3.3. During the following 7 days, without any locational movement, the flux peak increased slowly and exceeded the pre-storm fluxes by about 4 orders of magnitude. Subsequently, the decay rate of relativistic electrons is so slow that the peak remains over 104 cm-2\textperiodcenteredsr-1\textperiodcentereds-1 for about 30 days. The drift-resonance between ULF waves, which arose from high-speed solar wind and frequent impulses of solar wind dynamic pressure, and energetic electrons injected by substorms could be an important acceleration mechanism in this event. The local acceleration by whistler mode chorus could be another mechanism contributing to this enhancement. The plasmaspheric response to the interplanetary disturbances reveals that the enhanced outer zone is divided into two portions by the plasmapause. Accordingly, the slow loss rate in the plasmasphere due to hiss primarily contributed to the long-lived characteristic of this event. This event reveals that the outer zone population behaviors are dominated by the interplanetary variations together with the responses of geomagnetic field and plasmasphere to these variations. Yang, Xiao; Zhu, Guang; Zhang, Xiao; Sun, Yue; Liang, Jin; Wei, Xin; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014JA019797 Geomagnetic storm/substorm; Interplanetary magnetic field; Plasmapause; Relativistic electron; Solar wind |
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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 model consisting of a cold (a few tens of eV) population, a warm (a few hundred eV) anisotropic population, and a hot (a few keV) anisotropic population. The simulations use plasma and field parameters as measured from the satellite during this event except for two numbers: the anisotropies of the warm and the hot electron components are enhanced over the measured values in order to obtain relatively rapid instability growth. The simulations show that the warm component drives the quasi-electrostatic upper-band chorus, and that the hot component drives the electromagnetic lower-band chorus; the gap at \~ Ωe/2 is a natural consequence of the growth of two whistler modes with different properties. Fu, Xiangrong; Cowee, Misa; Friedel, Reinhard; Funsten, Herbert; Gary, Peter; Hospodarsky, George; Kletzing, Craig; Kurth, William; Larsen, Brian; Liu, Kaijun; MacDonald, Elizabeth; Min, Kyungguk; Reeves, Geoffrey; Skoug, Ruth; Winske, Dan; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014JA020364 |
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Magnetic search coils (MSCs) are sensitive to both magnetic and electric fields, but detecting electric fields is unnecessary for magnetic observations of plasma waves. However, it is important to evaluate both sensitivities for different geometries and electrostatic shields to avoid electric field pickup. An equivalent circuit model for the electric field sensitivity of an MSC in a collisionless isotropic cold plasma is developed here using electrical coupling through a sheath capacitance. That sensitivity is defined by a relationship between the MSC impedance and the sheath capacitance. To confirm the validity of the circuit model, the sensitivity to an electric field is measured by imposing an external electric field using charged parallel metallic plates in laboratory experiments. The coupling capacitance between the MSC and the charged plates is equivalent to the sheath capacitance in a space plasma. The measured results show good agreement with an approximate expression deduced from the equivalent circuit model. Ozaki, Mitsunori; Yagitani, Satoshi; Takahashi, Ken; Imachi, Tomohiko; Koji, Hiroki; Higashi, Ryoichi; Published by: IEEE Sensors Journal Published on: 10/2014 YEAR: 2014 DOI: 10.1109/JSEN.2014.2365495 electric field sensitivity; Magnetic search coils; sheath impedance; space plasmas |
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The Evolving Space Weather System - Van Allen Probes Contribution 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\textquoterights 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\textquoterights Van Allen Probes\textquoteright twin pair of satellites, launched in August of 2012 and orbiting directly through Earth\textquoterights severe radiation belts. The Van Allen Probes mission, formerly the Radiation Belt Storm Probes (RBSP, http://vanallenprobes.jhuapl.edu), were renamed soon after launch to honor the discoverer of Earth\textquoterights radiation belts at the beginning of the space age, the late James Van Allen (the spacecraft themselves are still referred to as RBSP-A and RBSP-B). The Van Allen Probes (Mauk et al., 2012 and other team contributions in the same special issue of Space Science Reviews, 2012) are one part of NASA\textquoterights Living With a Star (LWS, http://lws.gsfc.nasa.gov) program formulated to advance the scientific understanding of the connection between solar disturbances, the resulting heliospheric conditions and their effects on the geospace and Earth environment. Zanetti, L.; Mauk, B.; Fox, N.J.; Barnes, R.J.; Weiss, M.; Sotirelis, T.S.; Raouafi, N.-E.; Kessel, R.; Becker, H.; Published by: Space Weather Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014SW001108 |
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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\textendash500 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\textdegree phase shift between the poloidal mode Br and Ea suggests the standing poloidal waves in the Northern Hemisphere. Furthermore, the energetic electron flux modulations indicate that the azimuthal wave number is \~14. Direct evidence of drift resonance between the injected electrons and the excited poloidal ULF wave has been obtained. The resonant energy is estimated to be between 150 keV and 230 keV. Two possible scenaria on ULF wave triggering are discussed: vortex-like flow structure-driven field line resonance and ULF wave growth through drift resonance. It is found that the IP shock may trigger intense ULF wave and energetic electron behavior at L\~3 to 6 on the nightside, while the time profile of the wave is different from dayside cases. Hao, Y.; Zong, Q.-G.; Wang, Y.; Zhou, X.-Z.; Zhang, Hui; Fu, S; Pu, Z; Spence, H.; Blake, J.; Bonnell, J.; Wygant, J.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014JA020023 energetic particles; interplanetary shock; magnetotail ULF wave; poloidal and toroidal mode; Van Allen Probes; wave-particle interactions |
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We present simulations of the outer electron radiation belt using a new ULF wave-driven radial diffusion model, including empirical representations of loss due to chorus and plasmaspheric hiss. With an outer boundary condition constrained by in situ electron flux observations, we focus on the impacts of magnetopause shadowing and outward radial diffusion in the heart of the radiation belt. Third invariant conserving solutions are combined to simulate the L shell and time dependence of the differential flux at a fixed energy. Results for the geomagnetically quiet year of 2008 demonstrate not only remarkable cross L shell impacts from magnetopause shadowing but also excellent agreement with the in situ observations even though no internal acceleration source is included in the model. Our model demonstrates powerful utility for capturing the cross-L impacts of magnetopause shadowing with significant prospects for improved space weather forecasting. The potential role of the plasmasphere in creating a third belt is also discussed. Ozeke, Louis; Mann, Ian; Turner, Drew; Murphy, Kyle; Degeling, Alex; Rae, Jonathan; Milling, David; Published by: Geophysical Research Letters Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014GL060787 magnetopause shadowing; Radiation belt; ULF wave radial diffusion |