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D N Baker - One of the best experts on this subject based on the ideXlab platform.
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the global statistical response of the outer Radiation Belt during geomagnetic storms
Geophysical Research Letters, 2018Co-Authors: D L Turner, K R Murphy, C E J Watt, David G Sibeck, A J Boyd, C Forsyth, S G Claudepierre, Ian R. Mann, D N BakerAbstract:Using the total Radiation Belt electron content calculated from Van Allen Probe phase space density, the time-dependent and global response of the outer Radiation Belt during storms is statistically studied. Using phase space density reduces the impacts of adiabatic changes in the main phase, allowing a separation of adiabatic and nonadiabatic effects and revealing a clear modality and repeatable sequence of events in storm time Radiation Belt electron dynamics. This sequence exhibits an important first adiabatic invariant (μ)-dependent behavior in the seed (150 MeV/G), relativistic (1,000 MeV/G), and ultrarelativistic (4,000 MeV/G) populations. The outer Radiation Belt statistically shows an initial phase dominated by loss followed by a second phase of rapid acceleration, while the seed population shows little loss and immediate enhancement. The time sequence of the transition to the acceleration is also strongly μ dependent and occurs at low μ first, appearing to be repeatable from storm to storm.
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on the effect of geomagnetic storms on relativistic electrons in the outer Radiation Belt van allen probes observations
Journal of Geophysical Research, 2017Co-Authors: P S Moya, David G Sibeck, V A Pinto, Shrikanth G. Kanekal, D N BakerAbstract:Using Van Allen Probes ECT-REPT observations we performed a statistical study on the effect of geomagnetic storms on relativistic electrons fluxes in the outer Radiation Belt for 78 storms between September 2012 and June 2016. We found that the probability of enhancement, depletion and no change in flux values depends strongly on L and energy. Enhancement events are more common for ∼ 2 MeV electrons at L ∼ 5, and the number of enhancement events decreases with increasing energy at any given L shell. However, considering the percentage of occurrence of each kind of event, enhancements are more probable at higher energies, and the probability of enhancement tends to increases with increasing L shell. Depletion are more probable for 4-5 MeV electrons at the heart of the outer Radiation Belt, and no change events are more frequent at L 4.5 the probability of enhancement, depletion or no-change response presents little variation for all energies. Because these probabilities remain relatively constant as a function of radial distance in the outer Radiation Belt, measurements obtained at Geosynchronous orbit may be used as a proxy to monitor E≥1.8 MeV electrons in the outer Belt.
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understanding the mechanisms of Radiation Belt dropouts observed by van allen probes
Journal of Geophysical Research, 2017Co-Authors: S K Morley, Zheng Xiang, D N BakerAbstract:To achieve a better understanding of the dominant loss mechanisms for the rapid dropouts of Radiation Belt electrons, three distinct Radiation Belt dropout events observed by Van Allen Probes are comprehensively investigated. For each event, observations of the pitch angle distribution of electron fluxes and electromagnetic ion cyclotron (EMIC) waves are analyzed to determine the effects of atmospheric precipitation loss due to pitch angle scattering induced by EMIC waves. Last closed drift shells (LCDS) and magnetopause standoff position are obtained to evaluate the effects of magnetopause shadowing loss. Evolution of electron phase space density (PSD) versus L* profiles and the μ and K (first and second adiabatic invariants) dependence of the electron PSD drops are calculated to further analyze the dominant loss mechanisms at different L*. Our findings suggest that these Radiation Belt dropouts can be classified into distinct classes in terms of dominant loss mechanisms: magnetopause shadowing dominant, EMIC wave scattering dominant, and combination of both mechanisms. Different from previous understanding, our results show that magnetopause shadowing can deplete electrons at L* 4. Compared to the magnetopause standoff position, it is more reliable to use LCDS to evaluate the impact of magnetopause shadowing. The evolution of electron PSD versus L* profile and the μ, K dependence of electron PSD drops can provide critical and credible clues regarding the mechanisms responsible for electron losses at different L* over the outer Radiation Belt.
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explaining the dynamics of the ultra relativistic third van allen Radiation Belt
Nature Physics, 2016Co-Authors: I. R. Mann, D L Turner, K R Murphy, S G Claudepierre, D N Baker, L G Ozeke, I J Rae, A Kale, D K MillingAbstract:Since the discovery of the Van Allen Radiation Belts over 50 years ago, an explanation for their complete dynamics has remained elusive. Especially challenging is understanding the recently discovered ultra-relativistic third electron Radiation Belt. Current theory asserts that loss in the heart of the outer Belt, essential to the formation of the third Belt, must be controlled by high-frequency plasma wave–particle scattering into the atmosphere, via whistler mode chorus, plasmaspheric hiss, or electromagnetic ion cyclotron waves. However, this has failed to accurately reproduce the third Belt. Using a data-driven, time-dependent specification of ultra-low-frequency (ULF) waves we show for the first time how the third Radiation Belt is established as a simple, elegant consequence of storm-time extremely fast outward ULF wave transport. High-frequency wave–particle scattering loss into the atmosphere is not needed in this case. When rapid ULF wave transport coupled to a dynamic boundary is accurately specified, the sensitive dynamics controlling the enigmatic ultra-relativistic third Radiation Belt are naturally explained. The appearance of a third Radiation Belt in the Earth’s Van Allen Belts is difficult to explain using existing models for two Belts. However, a model based on ultra-low-frequency waves agrees quantitatively with measurements of the third Belt.
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nonstorm time dropout of Radiation Belt electron fluxes on 24 september 2013
Journal of Geophysical Research, 2016Co-Authors: Zhonglei Gao, G D Reeves, D N Baker, Huinan Zheng, Hui Zhu, Yuming Wang, Shui Wang, J. B. Blake, H E Spence, H O FunstenAbstract:Radiation Belt electron flux dropouts during the main phase of geomagnetic storms have received increasing attention in recent years. Here we focus on a rarely reported nonstorm time dropout event observed by Van Allen Probes on 24 September 2013. Within several hours, the Radiation Belt electron fluxes exhibited a significant (up to 2 orders of magnitude) depletion over a wide range of radial distances (L > 4.5), energies (~500 keV to several MeV) and equatorial pitch angles (0° ≤ αe ≤ 180°). STEERB simulations show that the relativistic electron loss in the region L = 4.5–6.0 was primarily caused by the pitch angle scattering of observed plasmaspheric hiss and electromagnetic ion cyclotron waves. Furthermore, our results emphasize the complexity of Radiation Belt dynamics and the importance of wave-driven precipitation loss even during nonstorm times.
Shrikanth G. Kanekal - One of the best experts on this subject based on the ideXlab platform.
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on the effect of geomagnetic storms on relativistic electrons in the outer Radiation Belt van allen probes observations
Journal of Geophysical Research, 2017Co-Authors: P S Moya, David G Sibeck, V A Pinto, Shrikanth G. Kanekal, D N BakerAbstract:Using Van Allen Probes ECT-REPT observations we performed a statistical study on the effect of geomagnetic storms on relativistic electrons fluxes in the outer Radiation Belt for 78 storms between September 2012 and June 2016. We found that the probability of enhancement, depletion and no change in flux values depends strongly on L and energy. Enhancement events are more common for ∼ 2 MeV electrons at L ∼ 5, and the number of enhancement events decreases with increasing energy at any given L shell. However, considering the percentage of occurrence of each kind of event, enhancements are more probable at higher energies, and the probability of enhancement tends to increases with increasing L shell. Depletion are more probable for 4-5 MeV electrons at the heart of the outer Radiation Belt, and no change events are more frequent at L 4.5 the probability of enhancement, depletion or no-change response presents little variation for all energies. Because these probabilities remain relatively constant as a function of radial distance in the outer Radiation Belt, measurements obtained at Geosynchronous orbit may be used as a proxy to monitor E≥1.8 MeV electrons in the outer Belt.
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highly relativistic Radiation Belt electron acceleration transport and loss large solar storm events of march and june 2015
Journal of Geophysical Research, 2016Co-Authors: D N Baker, Shrikanth G. Kanekal, J. B. Blake, A N Jaynes, S R Elkington, J C Foster, Philip J Erickson, J F Fennell, H Zhao, M G HendersonAbstract:Two of the largest geomagnetic storms of the last decade were witnessed in 2015. On 17 March 2015, a coronal mass ejection-driven event occurred with a Dst (storm time ring current index) value reaching -223 nT. On 22 June 2015 another strong storm (Dst reaching -204 nT) was recorded. These two storms each produced almost total loss of Radiation Belt high-energy (E ≳ 1 MeV) electron fluxes. Following the dropouts of Radiation Belt fluxes there were complex and rather remarkable recoveries of the electrons extending up to nearly 10 MeV in kinetic energy. The energized outer zone electrons showed a rich variety of pitch angle features including strong "butterfly" distributions with deep minima in flux at α = 90°. However, despite strong driving of outer zone earthward radial diffusion in these storms, the previously reported "impenetrable barrier" at L ≈ 2.8 was pushed inward, but not significantly breached, and no E ≳ 2.0 MeV electrons were seen to pass through the Radiation Belt slot region to reach the inner Van Allen zone. Overall, these intense storms show a wealth of novel features of acceleration, transport, and loss that are demonstrated in the present detailed analysis.
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source and seed populations for relativistic electrons their roles in Radiation Belt changes
Journal of Geophysical Research, 2015Co-Authors: A N Jaynes, S R Elkington, D N Baker, H J Singer, J V Rodriguez, T M Lotoaniu, A F Ali, Shrikanth G. KanekalAbstract:©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. Key Points Source/seed energy electrons required to produce MeV Radiation Belt energization Substorm injections lead to VLF wave growth, producing MeV acceleration ULF waves may enhance loss/acceleration due to increased outward/inward diffusion
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observations of the inner Radiation Belt crand and trapped solar protons
Journal of Geophysical Research, 2014Co-Authors: R S Selesnick, Shrikanth G. Kanekal, D N Baker, A N Jaynes, M K Hudson, B T KressAbstract:Measurements of inner Radiation Belt protons have been made by the Van Allen Probes Relativistic Electron-Proton Telescopes as a function of kinetic energy (24 to 76 MeV), equatorial pitch angle, and magnetic L shell, during late 2013 and early 2014. A probabilistic data analysis method reduces background from contamination by higher-energy protons. Resulting proton intensities are compared to predictions of a theoretical Radiation Belt model. Then trapped protons originating both from cosmic ray albedo neutron decay (CRAND) and from trapping of solar protons are evident in the measured distributions. An observed double-peaked distribution in L is attributed, based on the model comparison, to a gap in the occurrence of solar proton events during the 2007 to 2011 solar minimum. Equatorial pitch angle distributions show that trapped solar protons are confined near the magnetic equator but that CRAND protons can reach low altitudes. Narrow pitch angle distributions near the outer edge of the inner Belt are characteristic of proton trapping limits.
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the relativistic electron proton telescope rept instrument on board the Radiation Belt storm probes rbsp spacecraft characterization of earth s Radiation Belt high energy particle populations
Space Science Reviews, 2013Co-Authors: D N Baker, S R Elkington, Shrikanth G. Kanekal, V C Hoxie, Susan N Batiste, M Bolton, S Monk, R Reukauf, S Steg, J WestfallAbstract:Particle acceleration and loss in the million electron Volt (MeV) energy range (and above) is the least understood aspect of Radiation Belt science. In order to measure cleanly and separately both the energetic electron and energetic proton components, there is a need for a carefully designed detector system. The Relativistic Electron-Proton Telescope (REPT) on board the Radiation Belt Storm Probe (RBSP) pair of spacecraft consists of a stack of high-performance silicon solid-state detectors in a telescope configuration, a collimation aperture, and a thick case surrounding the detector stack to shield the sensors from penetrating Radiation and bremsstrahlung. The instrument points perpendicular to the spin axis of the spacecraft and measures high-energy electrons (up to ∼20 MeV) with excellent sensitivity and also measures magnetospheric and solar protons to energies well above E=100 MeV. The instrument has a large geometric factor (g=0.2 cm2 sr) to get reasonable count rates (above background) at the higher energies and yet will not saturate at the lower energy ranges. There must be fast enough electronics to avert undue dead-time limitations and chance coincidence effects. The key goal for the REPT design is to measure the directional electron intensities (in the range 10−2–106 particles/cm2 s sr MeV) and energy spectra (ΔE/E∼25 %) throughout the slot and outer Radiation Belt region. Present simulations and detailed laboratory calibrations show that an excellent design has been attained for the RBSP needs. We describe the engineering design, operational approaches, science objectives, and planned data products for REPT.
K R Murphy - One of the best experts on this subject based on the ideXlab platform.
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the global statistical response of the outer Radiation Belt during geomagnetic storms
Geophysical Research Letters, 2018Co-Authors: D L Turner, K R Murphy, C E J Watt, David G Sibeck, A J Boyd, C Forsyth, S G Claudepierre, Ian R. Mann, D N BakerAbstract:Using the total Radiation Belt electron content calculated from Van Allen Probe phase space density, the time-dependent and global response of the outer Radiation Belt during storms is statistically studied. Using phase space density reduces the impacts of adiabatic changes in the main phase, allowing a separation of adiabatic and nonadiabatic effects and revealing a clear modality and repeatable sequence of events in storm time Radiation Belt electron dynamics. This sequence exhibits an important first adiabatic invariant (μ)-dependent behavior in the seed (150 MeV/G), relativistic (1,000 MeV/G), and ultrarelativistic (4,000 MeV/G) populations. The outer Radiation Belt statistically shows an initial phase dominated by loss followed by a second phase of rapid acceleration, while the seed population shows little loss and immediate enhancement. The time sequence of the transition to the acceleration is also strongly μ dependent and occurs at low μ first, appearing to be repeatable from storm to storm.
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explaining the dynamics of the ultra relativistic third van allen Radiation Belt
Nature Physics, 2016Co-Authors: I. R. Mann, D L Turner, K R Murphy, S G Claudepierre, D N Baker, L G Ozeke, I J Rae, A Kale, D K MillingAbstract:Since the discovery of the Van Allen Radiation Belts over 50 years ago, an explanation for their complete dynamics has remained elusive. Especially challenging is understanding the recently discovered ultra-relativistic third electron Radiation Belt. Current theory asserts that loss in the heart of the outer Belt, essential to the formation of the third Belt, must be controlled by high-frequency plasma wave–particle scattering into the atmosphere, via whistler mode chorus, plasmaspheric hiss, or electromagnetic ion cyclotron waves. However, this has failed to accurately reproduce the third Belt. Using a data-driven, time-dependent specification of ultra-low-frequency (ULF) waves we show for the first time how the third Radiation Belt is established as a simple, elegant consequence of storm-time extremely fast outward ULF wave transport. High-frequency wave–particle scattering loss into the atmosphere is not needed in this case. When rapid ULF wave transport coupled to a dynamic boundary is accurately specified, the sensitive dynamics controlling the enigmatic ultra-relativistic third Radiation Belt are naturally explained. The appearance of a third Radiation Belt in the Earth’s Van Allen Belts is difficult to explain using existing models for two Belts. However, a model based on ultra-low-frequency waves agrees quantitatively with measurements of the third Belt.
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analytic expressions for ulf wave Radiation Belt radial diffusion coefficients
Journal of Geophysical Research, 2014Co-Authors: L G Ozeke, K R Murphy, I. R. Mann, Jonathan I Rae, D K MillingAbstract:We present analytic expressions for ULF wave-derived Radiation Belt radial diffusion coefficients, as a function of L and Kp, which can easily be incorporated into global Radiation Belt transport models. The diffusion coefficients are derived from statistical representations of ULF wave power, electric field power mapped from ground magnetometer data, and compressional magnetic field power from in situ measurements. We show that the overall electric and magnetic diffusion coefficients are to a good approximation both independent of energy. We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L). There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV—even though the model does not include the effects of local internal acceleration sources. Our results highlight not only the importance of correct specification of radial diffusion coefficients for developing accurate models but also show significant promise for Belt specification based on relatively simple models driven by solar wind parameters such as solar wind speed or geomagnetic indices such as Kp.
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ulf wave derived Radiation Belt radial diffusion coefficients
Journal of Geophysical Research, 2012Co-Authors: L G Ozeke, K R Murphy, I. R. Mann, Jonathan I Rae, D K Milling, S R Elkington, Anthony A Chan, H J SingerAbstract:[1] Waves in the ultra-low-frequency (ULF) band have frequencies which can be drift resonant with electrons in the outer Radiation Belt, suggesting the potential for strong interactions and enhanced radial diffusion. Previous radial diffusion coefficient models such as those presented by Brautigam and Albert (2000) have typically used semiempirical representations for both the ULF wave's electric and magnetic field power spectral densities (PSD) in space in the magnetic equatorial plane. In contrast, here we use ground- and space-based observations of ULF wave power to characterize the electric and magnetic diffusion coefficients. Expressions for the electric field power spectral densities are derived from ground-based magnetometer measurements of the magnetic field PSD, and in situ AMPTE and GOES spacecraft measurements are used to derive expressions for the compressional magnetic field PSD as functions of Kp, solar wind speed, and L-shell. Magnetic PSD results measured on the ground are mapped along the field line to give the electric field PSD in the equatorial plane assuming a guided Alfven wave solution and a thin sheet ionosphere. The ULF wave PSDs are then used to derive a set of new ULF-wave driven diffusion coefficients. These new diffusion coefficients are compared to estimates of the electric and magnetic field diffusion coefficients made by Brautigam and Albert (2000) and Brautigam et al. (2005). Significantly, our results, derived explicitly from ULF wave observations, indicate that electric field diffusion is much more important than magnetic field diffusion in the transport and energization of the Radiation Belt electrons.
Huinan Zheng - One of the best experts on this subject based on the ideXlab platform.
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Rapid Loss of Radiation Belt Relativistic Electrons by EMIC Waves
Journal of Geophysical Research: Space Physics, 2017Co-Authors: Zhonglei Gao, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Huinan Zheng, Yuming Wang, Shui Wang, John R WygantAbstract:How relativistic electrons are lost is an important question surrounding the complex dynamics of the Earth's outer Radiation Belt. Radial loss to the magnetopause and local loss to the atmosphere are two main competing paradigms. Here on the basis of the analysis of a Radiation Belt storm event on 27 February 2014, we present new evidence for the electromagnetic ion cyclotron (EMIC) wave-driven local precipitation loss of relativistic electrons in the heart of the outer Radiation Belt. During the main phase of this storm, the radial profile of relativistic electron phase space density was quasi-monotonic, qualitatively inconsistent with the prediction of radial loss theory. The local loss at low L shells was required to prevent the development of phase space density peak resulting from the radial loss process at high L shells. The rapid loss of relativistic electrons in the heart of outer Radiation Belt was observed as a dip structure of the electron flux temporal profile closely related to intense EMIC waves. Our simulations further confirm that the observed EMIC waves within a quite limited longitudinal region were able to reduce the off-equatorially mirroring relativistic electron fluxes by up to 2 orders of magnitude within about 1.5 h.
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nonstorm time dropout of Radiation Belt electron fluxes on 24 september 2013
Journal of Geophysical Research, 2016Co-Authors: Zhonglei Gao, G D Reeves, D N Baker, Huinan Zheng, Hui Zhu, Yuming Wang, Shui Wang, J. B. Blake, H E Spence, H O FunstenAbstract:Radiation Belt electron flux dropouts during the main phase of geomagnetic storms have received increasing attention in recent years. Here we focus on a rarely reported nonstorm time dropout event observed by Van Allen Probes on 24 September 2013. Within several hours, the Radiation Belt electron fluxes exhibited a significant (up to 2 orders of magnitude) depletion over a wide range of radial distances (L > 4.5), energies (~500 keV to several MeV) and equatorial pitch angles (0° ≤ αe ≤ 180°). STEERB simulations show that the relativistic electron loss in the region L = 4.5–6.0 was primarily caused by the pitch angle scattering of observed plasmaspheric hiss and electromagnetic ion cyclotron waves. Furthermore, our results emphasize the complexity of Radiation Belt dynamics and the importance of wave-driven precipitation loss even during nonstorm times.
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ultra low frequency wave driven diffusion of Radiation Belt relativistic electrons
Nature Communications, 2015Co-Authors: Hui Zhu, Fuliang Xiao, Huinan Zheng, Yuming Wang, Shui Wang, Q G Zong, X Z Zhou, Yixin Hao, Zhonglei Gao, D N BakerAbstract:Van Allen Radiation Belts are typically two zones of energetic particles encircling the Earth separated by the slot region. How the outer Radiation Belt electrons are accelerated to relativistic energies remains an unanswered question. Recent studies have presented compelling evidence for the local acceleration by very-low-frequency (VLF) chorus waves. However, there has been a competing theory to the local acceleration, radial diffusion by ultra-low-frequency (ULF) waves, whose importance has not yet been determined definitively. Here we report a unique Radiation Belt event with intense ULF waves but no detectable VLF chorus waves. Our results demonstrate that the ULF waves moved the inner edge of the outer Radiation Belt earthward 0.3 Earth radii and enhanced the relativistic electron fluxes by up to one order of magnitude near the slot region within about 10 h, providing strong evidence for the radial diffusion of Radiation Belt relativistic electrons.
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Chorus-driven acceleration of Radiation Belt electrons in the unusual temporal/spatial regions
2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014Co-Authors: Fuliang Xiao, Huinan Zheng, Hui ZhuAbstract:Cyclotron resonance with whistler-mode chorus waves is an important mechanism for the local acceleration of Radiation Belt energetic electrons. Such acceleration process has been widely investigated during the storm times, and its favored region is usually considered to be the low-density plasmatrough with magnetic local time (MLT) from midnight through dawn to noon. Here we present two case studies on the chorus-driven acceleration of Radiation Belt electrons in some “unusual” temporal /spatial regions. (1) The first event recorded by the Van Allen Probes during the nonstorm times from 21 to 23 February 2013. Within two days, a new Radiation Belt centering around L=5.8 formed and gradually merged with the original outer Belt. The corresponding relativistic electron fluxes increased by a factor of up to 50, accompanied by strong chorus waves. The quasi-linear STEERB model, including the local acceleration of detected chorus waves, can basically reproduce the observed 0.2–5.0 MeV electron flux enhancement at the center of new Belt. These results clearly illustrate the importance of chorus-driven local acceleration during the nonstorm times. (2) The second event observed by the Van Allen Probes in the duskside (MLT∼18) region on 2 October 2013. The quasi-linear diffusion analysis of STEERB code shows that, even in the duskside region with large ratio between the electron plasma frequency and the electron gyrofrequency, the detected intense (∼0.5 nT) chorus waves can still effectively accelerate Radiation Belt electrons. These results clearly exhibit the broader effective acceleration regions than usually estimated, at least for this one example.
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intense duskside lower band chorus waves observed by van allen probes generation and potential acceleration effect on Radiation Belt electrons
Journal of Geophysical Research, 2014Co-Authors: Fuliang Xiao, Huinan Zheng, Hui Zhu, Yuming Wang, Chao Shen, Chenglong Shen, Chong Wang, Rui LiuAbstract:Local acceleration driven by whistler mode chorus waves largely accounts for the enhancement of Radiation Belt relativistic electron fluxes, whose favored region is usually considered to be the plasmatrough with magnetic local time approximately from midnight through dawn to noon. On 2 October 2013, the Van Allen Probes recorded a rarely reported event of intense duskside lower band chorus waves (with power spectral density up to 10(-3)nT(2)/Hz) in the low-latitude region outside of L=5. Such chorus waves are found to be generated by the substorm-injected anisotropic suprathermal electrons and have a potentially strong acceleration effect on the Radiation Belt energetic electrons. This event study demonstrates the possibility of broader spatial regions with effective electron acceleration by chorus waves than previously expected. For such intense duskside chorus waves, the occurrence probability, the preferential excitation conditions, the time duration, and the accurate contribution to the long-term evolution of Radiation Belt electron fluxes may need further investigations in future.
R M Thorne - One of the best experts on this subject based on the ideXlab platform.
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modeling inward diffusion and slow decay of energetic electrons in the earth s outer Radiation Belt
Geophysical Research Letters, 2015Co-Authors: R M Thorne, G D Reeves, D N Baker, J. B. Blake, H E Spence, M G Henderson, C A Kletzing, W S Kurth, G B Hospodarsky, J F FennellAbstract:©2015. American Geophysical Union. All Rights Reserved. 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.
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Radiation Belt dynamics: The importance of wave‐particle interactions
Geophysical Research Letters, 2010Co-Authors: R M ThorneAbstract:[1] The flux of energetic electrons in the Earth's outer Radiation Belt can vary by several orders of magnitude over time scales less than a day, in response to changes in properties of the solar wind instigated by solar activity. Variability in the Radiation Belts is due to an imbalance between the dominant source and loss processes, caused by a violation of one or more of the adiabatic invariants. For Radiation Belt electrons, non-adiabatic behavior is primarily associated with energy and momentum transfer during interactions with various magnetospheric waves. A review is presented here of recent advances in both our understanding and global modeling of such wave-particle interactions, which have led to a paradigm shift in our understanding of electron acceleration in the Radiation Belts; internal local acceleration, rather than radial diffusion now appears to be the dominant acceleration process during the recovery phase of magnetic storms.
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Radiation Belt dynamics the importance of wave particle interactions
Geophysical Research Letters, 2010Co-Authors: R M ThorneAbstract:[1] The flux of energetic electrons in the Earth's outer Radiation Belt can vary by several orders of magnitude over time scales less than a day, in response to changes in properties of the solar wind instigated by solar activity. Variability in the Radiation Belts is due to an imbalance between the dominant source and loss processes, caused by a violation of one or more of the adiabatic invariants. For Radiation Belt electrons, non-adiabatic behavior is primarily associated with energy and momentum transfer during interactions with various magnetospheric waves. A review is presented here of recent advances in both our understanding and global modeling of such wave-particle interactions, which have led to a paradigm shift in our understanding of electron acceleration in the Radiation Belts; internal local acceleration, rather than radial diffusion now appears to be the dominant acceleration process during the recovery phase of magnetic storms.
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rapid scattering of Radiation Belt electrons by storm time emic waves
Geophysical Research Letters, 2010Co-Authors: Aleksandr Y. Ukhorskiy, Yuri Shprits, B J Anderson, K. Takahashi, R M ThorneAbstract:[1] A storm main phase can produce a rapid depletion of electron fluxes in the Earth's outer Radiation Belt and the pitch-angle scattering by the electromagnetic ion cyclotron (EMIC) waves is one mechanism that might account for the electron losses. To efficiently scatter the bulk of the electron population, below *1-2 MeV, the EMIC waves would need to have significant power very near a heavy ion gyrofrequency. We present a wave event at the storm main phase and carefully examine the wave spectrum to identify the energy range of electrons scattered by the waves. The EMIC waves exhibit power right below the He + gyrofrequency and we estimate that they can interact with electrons having energies as low as 400 keV producing rapid scattering at almost all pitch-angle values on the time scales of seconds. Our statistical analysis suggests that this event is not an exception; the majority of EMIC waves can scatter electrons with energies under 2 MeV. Our results show that EMIC waves can be one of the dominant Radiation Belt loss mechanisms during the storm main phase.
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parameterization of Radiation Belt electron loss timescales due to interactions with chorus waves
Geophysical Research Letters, 2007Co-Authors: Yuri Shprits, Nigel P. Meredith, R M ThorneAbstract:Wave-particle interactions lead to the loss of relativistic electrons from the outer Radiation Belt on timescales ranging from hours to weeks. For a fixed value of chorus wave amplitudes pitch-angle diffusion coefficients are computed for a range of energies and L, and are related to the loss rates of Radiation Belt electrons. By analyzing the dependence of the loss rates on L-value and energy we find functional dependencies for the lifetime of the Radiation Belt electrons. Parameters of the functional dependences are obtained using a linear regression technique. To create parameterizations of loss rate as a function of geomagnetic indices, we also analyzed the statistical data from day-side lower band chorus observations in the range of geomagnetic latitudes from 20° to 30°. The combined parameterizations of the wave amplitudes and scattering rates indicate that electron loss due to chorus waves strongly depends on energy and geomagnetic activity. During storm-time conditions the lifetimes of relativistic electrons, in the heart of the outer zone are on the order of a day and are on the scale of hours at lower energies. Pitch-angle scattering by chorus waves thus plays an important role in Radiation Belt dynamics. The developed parameterizations may be used in particle tracing codes and radial diffusion codes. The limitations of the parameterization, effect of scattering by other waves, and local acceleration processes are also discussed.
