22 results on '"Claudepierre SG"'
Search Results
2. Empirically Estimated Electron Lifetimes in the Earth's Radiation Belts: Van Allen Probe Observations
- Author
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Claudepierre, SG, Ma, Q, Bortnik, J, O'Brien, TP, Fennell, JF, and Blake, JB
- Subjects
decay ,lifetime ,loss ,pitch angle diffusion ,radiation belt ,wave particle interaction ,Meteorology & Atmospheric Sciences - Abstract
We use measurements from NASA's Van Allen Probes to calculate the decay time constants for electrons over a wide range of energies (30 keV to 4 MeV) and L values ( L = 1.3-6.0) in the Earth's radiation belts. Using an automated routine to identify flux decay events, we construct a large database of lifetimes for near-equatorially mirroring electrons over a 5-year interval. We provide the first accurate estimates of the long decay timescales in the inner zone ( ∼ 100 days), which are highly resolved in energy and free from proton contamination. In the slot region and outer zone, we compare our lifetime calculations with prior empirical estimates and find good quantitative agreement (lifetimes ∼ 1-20 days). The comparisons suggest that some prior estimates may overestimate electron lifetimes between L≈ 2.5-4.5 due to instrumental effects and/or background contamination. Previously reported two-stage decays are explicitly demonstrated to be a consequence of using integral fluxes.
- Published
- 2020
3. Empirically Estimated Electron Lifetimes in the Earth's Radiation Belts: Comparison With Theory
- Author
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Claudepierre, SG, Ma, Q, Bortnik, J, O'Brien, TP, Fennell, JF, and Blake, JB
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decay ,lifetime ,loss ,pitch angle diffusion ,radiation belt ,wave particle interaction ,Meteorology & Atmospheric Sciences - Abstract
We compute quasilinear diffusion rates due to pitch angle scattering by various mechanisms in the Earth's electron radiation belts. The calculated theoretical lifetimes are compared with observed decay rates, and we find excellent qualitative agreement between the two. The overall structure of the observed lifetime profiles as a function of energy and L is largely due to plasmaspheric hiss and Coulomb scattering. The results also reveal a local minimum in lifetimes in the inner zone at lower energy ( ∼ 50 keV), attributed to enhanced scattering via ground-based very low frequency transmitters, and a reduction in lifetimes at higher L and energy ( > 1 MeV), attributed to enhanced electromagnetic ion cyclotron wave scattering. In addition, we find significant quantitative disagreement at L
- Published
- 2020
4. Source and seed populations for relativistic electrons: Their roles in radiation belt changes
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Jaynes, AN, Baker, DN, Singer, HJ, Rodriguez, JV, Loto'aniu, TM, Ali, AF, Elkington, SR, Li, X, Kanekal, SG, Claudepierre, SG, Fennell, JF, Li, W, Thorne, RM, Kletzing, CA, Spence, HE, and Reeves, GD
- Subjects
radiation belts ,Van Allen Probes ,relativistic electrons ,VLF waves ,ULF waves ,substorms ,Astronomical and Space Sciences ,Atmospheric Sciences - Abstract
© 2015. American Geophysical Union. All Rights Reserved. Strong enhancements of outer Van Allen belt electrons have been shown to have a clear dependence on solar wind speed and on the duration of southward interplanetary magnetic field. However, individual case study analyses also have demonstrated that many geomagnetic storms produce little in the way of outer belt enhancements and, in fact, may produce substantial losses of relativistic electrons. In this study, focused upon a key period in August-September 2014, we use GOES geostationary orbit electron flux data and Van Allen Probes particle and fields data to study the process of radiation belt electron acceleration. One particular interval, 13-22 September, initiated by a short-lived geomagnetic storm and characterized by a long period of primarily northward interplanetary magnetic field (IMF), showed strong depletion of relativistic electrons (including an unprecedented observation of long-lasting depletion at geostationary orbit) while an immediately preceding, and another immediately subsequent, storm showed strong radiation belt enhancement. We demonstrate with these data that two distinct electron populations resulting from magnetospheric substorm activity are crucial elements in the ultimate acceleration of highly relativistic electrons in the outer belt: the source population (tens of keV) that give rise to VLF wave growth and the seed population (hundreds of keV) that are, in turn, accelerated through VLF wave interactions to much higher energies. ULF waves may also play a role by either inhibiting or enhancing this process through radial diffusion effects. If any components of the inner magnetospheric accelerator happen to be absent, the relativistic radiation belt enhancement fails to materialize.
- Published
- 2015
5. Modeling inward diffusion and slow decay of energetic electrons in the Earth's outer radiation belt
- Author
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Ma, Q, Li, W, Thorne, RM, Ni, B, Kletzing, CA, Kurth, WS, Hospodarsky, GB, Reeves, GD, Henderson, MG, Spence, HE, Baker, DN, Blake, JB, Fennell, JF, Claudepierre, SG, and Angelopoulos, V
- Subjects
Meteorology & Atmospheric Sciences - Abstract
A new 3-D diffusion code is used to investigate the inward intrusion and slow decay of energetic radiation belt electrons (>0.5MeV) observed by the Van Allen Probes during a 10day quiet period on March 2013. During the inward transport, the peak differential electron fluxes decreased by approximately an order of magnitude at various energies. Our 3-D 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 time scales and the pitch angle distributions in our simulation are consistent with the Van Allen Probe observations over multiple energy channels. Our study suggests that the quiet time energetic electron dynamics are effectively controlled by inward radial diffusion and pitch angle scattering due to a combination of plasmaspheric hiss and EMIC waves in the Earth's radiation belts.
- Published
- 2015
6. Modeling Inner Proton Belt Variability at Energies 1 to 10 MeV Using BAS-PRO
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Lozinski, AR, Horne, RB, Glauert, SA, Del Zanna, G, and Claudepierre, SG
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radial diffusion ,solar cell degradation ,Physics::Space Physics ,modeling ,Astrophysics::Earth and Planetary Astrophysics ,proton belt ,Nuclear Experiment ,trapped protons - Abstract
Geomagnetically trapped protons forming Earth's proton radiation belt pose a hazard to orbiting spacecraft. In particular, solar cell degradation is caused by non‐ionising collisions with protons at energies of several megaelectron volts (MeV), which can shorten mission lifespan. Dynamic enhancements in trapped proton flux following solar energetic particle events have been observed to last several months, and there is a strong need for physics‐based modeling to predict the impact on spacecraft. However, modeling proton belt variability at this energy is challenging because radial diffusion coefficients are not well constrained. We address this by using the British Antarctic Survey proton belt model BAS‐PRO to perform 3D simulations of the proton belt in the region 1.15 ≤ L ≤ 2 from 2014 to 2018. The model is driven by measurements from the Radiation Belt Storm Probes Ion Composition Experiment and Magnetic Electron Ion Spectrometer instruments carried by the Van Allen Probe satellites. To investigate sensitivity, simulations are repeated for three different sets of proton radial diffusion coefficients D LL taken from previous literature. Comparing the time evolution of each result, we find that solar cycle variability can drive up to a ∼75% increase in 7.5 MeV flux at L = 1.3 over four years due to the increased importance of collisional loss at low energies. We also show how the anisotropy of proton pitch angle distributions varies with L and energy, depending on D LL . However we find that phase space density can vary by three orders of magnitude at L = 1.4 and μ = 20 MeV/G due to uncertainty in D LL , highlighting the need to better constrain proton D LL at low energy.
- Published
- 2022
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7. Modeling Inner Proton Belt Variability at Energies 1 to 10 MeV Using BAS-PRO
- Author
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Lozinski, AR, Horne, RB, Glauert, SA, Del Zanna, G, Claudepierre, SG, Lozinski, AR [0000-0002-6508-487X], Horne, RB [0000-0002-0412-6407], Glauert, SA [0000-0003-0149-8608], Del Zanna, G [0000-0002-4125-0204], Claudepierre, SG [0000-0001-5513-5947], and Apollo - University of Cambridge Repository
- Subjects
radial diffusion ,solar cell degradation ,Physics::Space Physics ,modeling ,Astrophysics::Earth and Planetary Astrophysics ,proton belt ,Nuclear Experiment ,trapped protons - Abstract
Geomagnetically trapped protons forming Earth's proton radiation belt pose a hazard to orbiting spacecraft. In particular, solar cell degradation is caused by non‐ionising collisions with protons at energies of several megaelectron volts (MeV), which can shorten mission lifespan. Dynamic enhancements in trapped proton flux following solar energetic particle events have been observed to last several months, and there is a strong need for physics‐based modeling to predict the impact on spacecraft. However, modeling proton belt variability at this energy is challenging because radial diffusion coefficients are not well constrained. We address this by using the British Antarctic Survey proton belt model BAS‐PRO to perform 3D simulations of the proton belt in the region 1.15 ≤ L ≤ 2 from 2014 to 2018. The model is driven by measurements from the Radiation Belt Storm Probes Ion Composition Experiment and Magnetic Electron Ion Spectrometer instruments carried by the Van Allen Probe satellites. To investigate sensitivity, simulations are repeated for three different sets of proton radial diffusion coefficients D LL taken from previous literature. Comparing the time evolution of each result, we find that solar cycle variability can drive up to a ∼75% increase in 7.5 MeV flux at L = 1.3 over four years due to the increased importance of collisional loss at low energies. We also show how the anisotropy of proton pitch angle distributions varies with L and energy, depending on D LL . However we find that phase space density can vary by three orders of magnitude at L = 1.4 and μ = 20 MeV/G due to uncertainty in D LL , highlighting the need to better constrain proton D LL at low energy.
- Published
- 2021
8. Collaborative Research Activities of the Arase and Van Allen Probes.
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Miyoshi Y, Shinohara I, Ukhorskiy S, Claudepierre SG, Mitani T, Takashima T, Hori T, Santolik O, Kolmasova I, Matsuda S, Kasahara Y, Teramoto M, Katoh Y, Hikishima M, Kojima H, Kurita S, Imajo S, Higashio N, Kasahara S, Yokota S, Asamura K, Kazama Y, Wang SY, Jun CW, Kasaba Y, Kumamoto A, Tsuchiya F, Shoji M, Nakamura S, Kitahara M, Matsuoka A, Shiokawa K, Seki K, Nosé M, Takahashi K, Martinez-Calderon C, Hospodarsky G, Colpitts C, Kletzing C, Wygant J, Spence H, Baker DN, Reeves GD, Blake JB, and Lanzerotti L
- Abstract
This paper presents the highlights of joint observations of the inner magnetosphere by the Arase spacecraft, the Van Allen Probes spacecraft, and ground-based experiments integrated into spacecraft programs. The concurrent operation of the two missions in 2017-2019 facilitated the separation of the spatial and temporal structures of dynamic phenomena occurring in the inner magnetosphere. Because the orbital inclination angle of Arase is larger than that of Van Allen Probes, Arase collected observations at higher L -shells up to L ∼ 10 . After March 2017, similar variations in plasma and waves were detected by Van Allen Probes and Arase. We describe plasma wave observations at longitudinally separated locations in space and geomagnetically-conjugate locations in space and on the ground. The results of instrument intercalibrations between the two missions are also presented. Arase continued its normal operation after the scientific operation of Van Allen Probes completed in October 2019. The combined Van Allen Probes (2012-2019) and Arase (2017-present) observations will cover a full solar cycle. This will be the first comprehensive long-term observation of the inner magnetosphere and radiation belts., (© The Author(s) 2022.)
- Published
- 2022
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9. The Magnetic Electron Ion Spectrometer: A Review of On-Orbit Sensor Performance, Data, Operations, and Science.
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Claudepierre SG, Blake JB, Boyd AJ, Clemmons JH, Fennell JF, Gabrielse C, Looper MD, Mazur JE, O'Brien TP, Reeves GD, Roeder JL, Spence HE, and Turner DL
- Abstract
Measurements from NASA's Van Allen Probes have transformed our understanding of the dynamics of Earth's geomagnetically-trapped, charged particle radiation. The Van Allen Probes were equipped with the Magnetic Electron Ion Spectrometers (MagEIS) that measured energetic and relativistic electrons, along with energetic ions, in the radiation belts. Accurate and routine measurement of these particles was of fundamental importance towards achieving the scientific goals of the mission. We provide a comprehensive review of the MagEIS suite's on-orbit performance, operation, and data products, along with a summary of scientific results. The purpose of this review is to serve as a complement to the MagEIS instrument paper, which was largely completed before flight and thus focused on pre-flight design and performance characteristics. As is the case with all space-borne instrumentation, the anticipated sensor performance was found to be different once on orbit. Our intention is to provide sufficient detail on the MagEIS instruments so that future generations of researchers can understand the subtleties of the sensors, profit from these unique measurements, and continue to unlock the mysteries of the near-Earth space radiation environment., Supplementary Information: The online version contains supplementary material available at 10.1007/s11214-021-00855-2., Competing Interests: Conflicts of interest/Competing interestsThe authors declare that they have no conflict of interest that could have direct or potential influence or impart bias on this work., (© The Author(s) 2021.)
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- 2021
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10. Very-Low-Frequency transmitters bifurcate energetic electron belt in near-earth space.
- Author
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Hua M, Li W, Ni B, Ma Q, Green A, Shen X, Claudepierre SG, Bortnik J, Gu X, Fu S, Xiang Z, and Reeves GD
- Abstract
Very-Low-Frequency (VLF) transmitters operate worldwide mostly at frequencies of 10-30 kilohertz for submarine communications. While it has been of intense scientific interest and practical importance to understand whether VLF transmitters can affect the natural environment of charged energetic particles, for decades there remained little direct observational evidence that revealed the effects of these VLF transmitters in geospace. Here we report a radially bifurcated electron belt formation at energies of tens of kiloelectron volts (keV) at altitudes of ~0.8-1.5 Earth radii on timescales over 10 days. Using Fokker-Planck diffusion simulations, we provide quantitative evidence that VLF transmitter emissions that leak from the Earth-ionosphere waveguide are primarily responsible for bifurcating the energetic electron belt, which typically exhibits a single-peak radial structure in near-Earth space. Since energetic electrons pose a potential danger to satellite operations, our findings demonstrate the feasibility of mitigation of natural particle radiation environment.
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- 2020
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11. Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study.
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Motoba T, Ohtani S, Claudepierre SG, Reeves GD, Ukhorskiy AY, and Lanzerotti LJ
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Four closely located satellites at and inside geosynchronous orbit (GEO) provided a great opportunity to study the dynamical evolution and spatial scale of premidnight energetic particle injections inside GEO during a moderate substorm on 23 December 2016. Just following the substorm onset, the four spacecraft, a LANL satellite at GEO, the two Van Allen Probes (also called "RBSP") at ~5.8 R
E , and a THEMIS satellite at ~5.3 RE , observed substorm-related particle injections and local dipolarizations near the central meridian (~22 MLT) of a wedge-like current system. The large-scale evolution of the electron and ion (H, He, and O) injections was almost identical at the two RBSP spacecraft with ~0.5 RE apart. However, the initial short-timescale particle injections exhibited a striking difference between RBSP-A and -B: RBSP-B observed an energy dispersionless injection which occurred concurrently with a transient, strong dipolarization front (DF) with a peak-to-peak amplitude of ~25 nT over ~25 s; RBSP-A measured a dispersed/weaker injection with no corresponding DF. The spatiotemporally localized DF was accompanied by an impulsive, westward electric field (~20 mV m-1 ). The fast, impulsive E × B drift caused the radial transport of the electron and ion injection regions from GEO to ~5.8 RE . The penetrating DF fields significantly altered the rapid energy- and pitch angle-dependent flux changes of the electrons and the H and He ions inside GEO. Such flux distributions could reflect the transient DF-related particle acceleration and/or transport processes occurring inside GEO. In contrast, O ions were little affected by the DF fields., (©2020. The Authors.)- Published
- 2020
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12. Electron Microburst Size Distribution Derived With AeroCube-6.
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Shumko M, Johnson AT, Sample JG, Griffith BA, Turner DL, O'Brien TP, Agapitov O, Blake JB, and Claudepierre SG
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Microbursts are an impulsive increase of electrons from the radiation belts into the atmosphere and have been directly observed in low Earth orbit and the upper atmosphere. Prior work has estimated that microbursts are capable of rapidly depleting the radiation belt electrons on the order of a day; hence, their role to radiation belt electron losses must be considered. Losses due to microbursts are not well constrained, and more work is necessary to accurately quantify their contribution as a loss process. To address this question, we present a statistical study of > 35 keV microburst sizes using the pair of AeroCube-6 CubeSats. The microburst size distribution in low Earth orbit and the magnetic equator was derived using both spacecraft. In low Earth orbit, the majority of microbursts were observed, while the AeroCube-6 separation was less than a few tens of kilometers, mostly in latitude. To account for the statistical effects of random microburst locations and sizes, Monte Carlo and analytic models were developed to test hypothesized microburst size distributions. A family of microburst size distributions were tested, and a Markov chain Monte Carlo sampler was used to estimate the optimal distribution of model parameters. Finally, a majority of observed microbursts map to sizes less than 200 km at the magnetic equator. Since microbursts are widely believed to be generated by scattering of radiation belt electrons by whistler mode waves, the observed microburst size distribution was compared to whistler mode chorus size distributions derived in prior literature., (©2020. The Authors.)
- Published
- 2020
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13. RBSP-ECT Combined Spin-Averaged Electron Flux Data Product.
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Boyd AJ, Reeves GD, Spence HE, Funsten HO, Larsen BA, Skoug RM, Blake JB, Fennell JF, Claudepierre SG, Baker DN, Kanekal SG, and Jaynes AN
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We describe a new data product combining the spin-averaged electron flux measurements from the Radiation Belt Storm Probes (RBSP) Energetic Particle Composition and Thermal Plasma (ECT) suite on the National Aeronautics and Space Administration's Van Allen Probes. We describe the methodology used to combine each of the data sets and produce a consistent set of spectra for September 2013 to the present. Three-minute-averaged flux spectra are provided spanning energies from 15 eV up to 20 MeV. This new data product provides additional utility to the ECT data and offers a consistent cross calibrated data set for researchers interested in examining the dynamics of the inner magnetosphere across a wide range of energies., (©2019. The Authors.)
- Published
- 2019
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14. A Revised Look at Relativistic Electrons in the Earth's Inner Radiation Zone and Slot Region.
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Claudepierre SG, O'Brien TP, Looper MD, Blake JB, Fennell JF, Roeder JL, Clemmons JH, Mazur JE, Turner DL, Reeves GD, and Spence HE
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We describe a new, more accurate procedure for estimating and removing inner zone background contamination from Van Allen Probes Magnetic Electron Ion Spectrometer (MagEIS) radiation belt measurements. This new procedure is based on the underlying assumption that the primary source of background contamination in the electron measurements at L shells less than three, energetic inner belt protons, is relatively stable. Since a magnetic spectrometer can readily distinguish between foreground electrons and background signals, we are able to exploit the proton stability to construct a model of the background contamination in each MagEIS detector by only considering times when the measurements are known to be background dominated. We demonstrate, for relativistic electron measurements in the inner zone, that the new technique is a significant improvement upon the routine background corrections that are used in the standard MagEIS data processing, which can "overcorrect" and therefore remove real (but small) electron fluxes. As an example, we show that the previously reported 1-MeV injection into the inner zone that occurred in June of 2015 was distributed more broadly in L and persisted in the inner zone longer than suggested by previous estimates. Such differences can have important implications for both scientific studies and spacecraft engineering applications that make use of MagEIS electron data in the inner zone at relativistic energies. We compare these new results with prior work and present more recent observations that also show a 1-MeV electron injection into the inner zone following the September 2017 interplanetary shock passage.
- Published
- 2019
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15. Determining the Mode, Frequency, and Azimuthal Wave Number of ULF Waves During a HSS and Moderate Geomagnetic Storm.
- Author
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Murphy KR, Inglis AR, Sibeck DG, Rae IJ, Watt CEJ, Silveira M, Plaschke F, Claudepierre SG, and Nakamura R
- Abstract
Ultralow frequency (ULF) waves play a fundamental role in the dynamics of the inner magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion, and discrete ULF wave power can energize electrons through a resonant interaction. Using observations from the Magnetospheric Multiscale mission, we characterize the evolution of ULF waves during a high-speed solar wind stream (HSS) and moderate geomagnetic storm while there is an enhancement of the outer radiation belt. The Automated Flare Inference of Oscillations code is used to distinguish discrete ULF wave power from broadband wave power during the HSS. During periods of discrete wave power and utilizing the close separation of the Magnetospheric Multiscale spacecraft, we estimate the toroidal mode ULF azimuthal wave number throughout the geomagnetic storm. We concentrate on the toroidal mode as the HSS compresses the dayside magnetosphere resulting in an asymmetric magnetic field topology where toroidal mode waves can interact with energetic electrons. Analysis of the mode structure and wave numbers demonstrates that the generation of the observed ULF waves is a combination of externally driven waves, via the Kelvin-Helmholtz instability, and internally driven waves, via unstable ion distributions. Further analysis of the periods and toroidal azimuthal wave numbers suggests that these waves can couple with the core electron radiation belt population via the drift resonance during the storm. The azimuthal wave number and structure of ULF wave power (broadband or discrete) have important implications for the inner magnetospheric and radiation belt dynamics., (©2018. The Authors.)
- Published
- 2018
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16. Explaining the apparent impenetrable barrier to ultra-relativistic electrons in the outer Van Allen belt.
- Author
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Ozeke LG, Mann IR, Murphy KR, Degeling AW, Claudepierre SG, and Spence HE
- Abstract
Recent observations have shown the existence of an apparent impenetrable barrier at the inner edge of the ultra-relativistic outer electron radiation belt. This apparent impenetrable barrier has not been explained. However, recent studies have suggested that fast loss, such as associated with scattering into the atmosphere from man-made very-low frequency transmissions, is required to limit the Earthward extent of the belt. Here we show that the steep flux gradient at the implied barrier location is instead explained as a natural consequence of ultra-low frequency wave radial diffusion. Contrary to earlier claims, sharp boundaries in fast loss processes at the barrier are not needed. Moreover, we show that penetration to the barrier can occur on the timescale of days rather than years as previously reported, with the Earthward extent of the belt being limited by the finite duration of strong solar wind driving, which can encompass only a single geomagnetic storm.
- Published
- 2018
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17. Energy-dependent dynamics of keV to MeV electrons in the inner zone, outer zone, and slot regions.
- Author
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Reeves GD, Friedel RH, Larsen BA, Skoug RM, Funsten HO, Claudepierre SG, Fennell JF, Turner DL, Denton MH, Spence HE, Blake JB, and Baker DN
- Abstract
We present observations of the radiation belts from the Helium Oxygen Proton Electron and Magnetic Electron Ion Spectrometer particle detectors on the Van Allen Probes satellites that illustrate the energy dependence and L shell dependence of radiation belt enhancements and decays. We survey events in 2013 and analyze an event on 1 March in more detail. The observations show the following: (a) at all L shells, lower energy electrons are enhanced more often than higher energies; (b) events that fill the slot region are more common at lower energies; (c) enhancements of electrons in the inner zone are more common at lower energies; and (d) even when events do not fully fill the slot region, enhancements at lower energies tend to extend to lower L shells than higher energies. During enhancement events the outer zone extends to lower L shells at lower energies while being confined to higher L shells at higher energies. The inner zone shows the opposite with an outer boundary at higher L shells for lower energies. Both boundaries are nearly straight in log(energy) versus L shell space. At energies below a few 100 keV, radiation belt electron penetration through the slot region into the inner zone is commonplace, but the number and frequency of "slot filling" events decreases with increasing energy. The inner zone is enhanced only at energies that penetrate through the slot. Energy- and L shell-dependent losses (that are consistent with whistler hiss interactions) return the belts to more quiescent conditions.
- Published
- 2016
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18. Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere.
- Author
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Claudepierre SG, Toffoletto FR, and Wiltberger M
- Abstract
We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics.
- Published
- 2016
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19. Global storm time depletion of the outer electron belt.
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Ukhorskiy AY, Sitnov MI, Millan RM, Kress BT, Fennell JF, Claudepierre SG, and Barnes RJ
- 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 orders of magnitude at different spatial and temporal scales. 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 loss to the rapid depletion of the outer belt observed at the Van Allen Probes spacecraft during the main phase of 17 March 2013 storm. The intensities of >1 MeV electrons were depleted by more than an order of magnitude over the entire radial extent of the belt in less than 6 h after the sudden storm commencement. For the analysis we used three-dimensional test particle simulations of global evolution of the outer belt in the Tsyganenko-Sitnov (TS07D) magnetic field model with an inductive electric field. Comparison of the simulation results with electron measurements from the Magnetic Electron Ion Spectrometer experiment shows that magnetopause loss accounts for most of the observed depletion at L >5, while at lower L shells the depletion is adiabatic. Both magnetopause loss and the adiabatic effect are controlled by the change in global configuration of the magnetic field due to storm time development of the ring current; a simulation of electron evolution without a ring current produces a much weaker depletion.
- Published
- 2015
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20. Rapid local acceleration of relativistic radiation-belt electrons by magnetospheric chorus.
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Thorne RM, Li W, Ni B, Ma Q, Bortnik J, Chen L, Baker DN, Spence HE, Reeves GD, Henderson MG, Kletzing CA, Kurth WS, Hospodarsky GB, Blake JB, Fennell JF, Claudepierre SG, and Kanekal SG
- Abstract
Recent analysis of satellite data obtained during the 9 October 2012 geomagnetic storm identified the development of peaks in electron phase space density, which are compelling evidence for local electron acceleration in the heart of the outer radiation belt, but are inconsistent with acceleration by inward radial diffusive transport. However, the precise physical mechanism responsible for the acceleration on 9 October was not identified. Previous modelling has indicated that a magnetospheric electromagnetic emission known as chorus could be a potential candidate for local electron acceleration, but a definitive resolution of the importance of chorus for radiation-belt acceleration was not possible because of limitations in the energy range and resolution of previous electron observations and the lack of a dynamic global wave model. Here we report high-resolution electron observations obtained during the 9 October storm and demonstrate, using a two-dimensional simulation performed with a recently developed time-varying data-driven model, that chorus scattering explains the temporal evolution of both the energy and angular distribution of the observed relativistic electron flux increase. Our detailed modelling demonstrates the remarkable efficiency of wave acceleration in the Earth's outer radiation belt, and the results presented have potential application to Jupiter, Saturn and other magnetized astrophysical objects.
- Published
- 2013
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21. Electron acceleration in the heart of the Van Allen radiation belts.
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Reeves GD, Spence HE, Henderson MG, Morley SK, Friedel RH, Funsten HO, Baker DN, Kanekal SG, Blake JB, Fennell JF, Claudepierre SG, Thorne RM, Turner DL, Kletzing CA, Kurth WS, Larsen BA, and Niehof JT
- Abstract
The Van Allen radiation belts contain ultrarelativistic electrons trapped in Earth's magnetic field. Since their discovery in 1958, a fundamental unanswered question has been how electrons can be accelerated to such high energies. Two classes of processes have been proposed: transport and acceleration of electrons from a source population located outside the radiation belts (radial acceleration) or acceleration of lower-energy electrons to relativistic energies in situ in the heart of the radiation belts (local acceleration). We report measurements from NASA's Van Allen Radiation Belt Storm Probes that clearly distinguish between the two types of acceleration. The observed radial profiles of phase space density are characteristic of local acceleration in the heart of the radiation belts and are inconsistent with a predominantly radial acceleration process.
- Published
- 2013
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22. A long-lived relativistic electron storage ring embedded in Earth's outer Van Allen belt.
- Author
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Baker DN, Kanekal SG, Hoxie VC, Henderson MG, Li X, Spence HE, Elkington SR, Friedel RH, Goldstein J, Hudson MK, Reeves GD, Thorne RM, Kletzing CA, and Claudepierre SG
- Abstract
Since their discovery more than 50 years ago, Earth's Van Allen radiation belts have been considered to consist of two distinct zones of trapped, highly energetic charged particles. The outer zone is composed predominantly of megaelectron volt (MeV) electrons that wax and wane in intensity on time scales ranging from hours to days, depending primarily on external forcing by the solar wind. The spatially separated inner zone is composed of commingled high-energy electrons and very energetic positive ions (mostly protons), the latter being stable in intensity levels over years to decades. In situ energy-specific and temporally resolved spacecraft observations reveal an isolated third ring, or torus, of high-energy (>2 MeV) electrons that formed on 2 September 2012 and persisted largely unchanged in the geocentric radial range of 3.0 to ~3.5 Earth radii for more than 4 weeks before being disrupted (and virtually annihilated) by a powerful interplanetary shock wave passage.
- Published
- 2013
- Full Text
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