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Daniel N. Baker - One of the best experts on this subject based on the ideXlab platform.
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The Impenetrable Barrier: Suppression of Chorus Wave Growth by VLF Transmitters
Journal of Geophysical Research, 2020Co-Authors: John C. Foster, Philip J. Erickson, Yoshiharu Omura, Daniel N. BakerAbstract:Rapid radiation belt recovery following storm time depletion involves Local Acceleration of multi-MeV electrons in nonlinear interactions with VLF chorus waves. Previous studies of an apparent impe...
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Radiation belt electron Acceleration by chorus waves during the 17 March 2013 storm
Journal of Geophysical Research, 2014Co-Authors: Richard M. Thorne, Jacob Bortnik, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Shrikanth G. Kanekal, Janet C. GreenAbstract:Local Acceleration driven by whistler-mode chorus waves is fundamentally important for accelerating seed electron populations to highly relativistic energies in the outer radiation belt. In this study, we quantitatively evaluate chorus-driven electron Acceleration during the 17 March 2013 storm, when the Van Allen Probes observed very rapid electron Acceleration up to several MeV within ~12 hours. A clear radial peak in electron phase space density (PSD) observed near L* ~4 indicates that an internal Local Acceleration process was operating. We construct the global distribution of chorus wave intensity from the low-altitude electron measurements made by multiple Polar Orbiting Environmental Satellites (POES) satellites over a broad region, which is ultimately used to simulate the radiation belt electron dynamics driven by chorus waves. Our simulation results show remarkable agreement in magnitude, timing, energy dependence, and pitch angle distribution with the observed electron PSD near its peak location. However, radial diffusion and other loss processes may be required to explain the differences between the observation and simulation at other locations away from the PSD peak. Our simulation results, together with previous studies, suggest that Local Acceleration by chorus waves is a robust and ubiquitous process and plays a critical role in accelerating injected seed electrons with convective energies (~100 keV) to highly relativistic energies (several MeV).
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Rapid Local Acceleration of relativistic radiation-belt electrons by magnetospheric chorus
Nature, 2013Co-Authors: Richard M. Thorne, Jacob Bortnik, Lunjin Chen, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Michael G. HendersonAbstract:High-resolution measurements of electrons obtained by satellite during the geomagnetic storm of 9 October 2012 together with a data-driven global wave model are analysed to show that scattering by a magnetospheric electromagnetic emission, known as ‘chorus’, can explain the temporal evolution of the observed increase in relativistic electron flux. A magnetic storm that occurred on 9 October 2012 has been analysed in detail using the array of instruments onboard NASA's two Van Allen probes, launched in August 2012 to study Earth's magnetosphere, including the Van Allen radiation belt. The nature of the force that accelerates electrons trapped in the radiation belts has been a topic of much debate centering on whether the electrons are accelerated Locally or by radial diffusive transport between weak and strong magnetic fields. Initial results had favoured a Local mechanism and now Richard Thorne et al. report high-resolution electron observations from Van Allen probe A, together with modelling studies that identify the likely source of accelerating energy as chorus scattering, an effect caused Locally by structured wave formations. This powerful Local Acceleration is also likely to be a factor around Jupiter, Saturn and other bodies with significant magnetic fields. Recent analysis of satellite data obtained during the 9 October 2012 geomagnetic storm identified the development of peaks in electron phase space density1, which are compelling evidence for Local electron Acceleration in the heart of the outer radiation belt2,3, but are inconsistent with Acceleration by inward radial diffusive transport4,5. 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 Acceleration6,7,8,9,10, 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 observations11 obtained during the 9 October storm and demonstrate, using a two-dimensional simulation performed with a recently developed time-varying data-driven model12, 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.
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rapid Local Acceleration of relativistic radiation belt electrons by magnetospheric chorus
Nature, 2013Co-Authors: Richard M. Thorne, Jacob Bortnik, W. Li, Lunjin Chen, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Michael G. Henderson, Binbin Ni, Craig KletzingAbstract:High-resolution measurements of electrons obtained by satellite during the geomagnetic storm of 9 October 2012 together with a data-driven global wave model are analysed to show that scattering by a magnetospheric electromagnetic emission, known as ‘chorus’, can explain the temporal evolution of the observed increase in relativistic electron flux.
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Electron Acceleration in the Heart of the Van Allen Radiation Belts
Science, 2013Co-Authors: Geoffrey D. Reeves, Daniel N. Baker, Harlan E. Spence, Michael G. Henderson, Steven K. Morley, R. H. W. Friedel, Herbert O. Funsten, Shrikanth G. Kanekal, J. B. Blake, Joseph F. FennellAbstract: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.
Geoffrey D. Reeves - One of the best experts on this subject based on the ideXlab platform.
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Quantitative Evaluation of Radial Diffusion and Local Acceleration Processes During GEM Challenge Events
Journal of Geophysical Research, 2018Co-Authors: Jacob Bortnik, Richard M. Thorne, Geoffrey D. Reeves, Craig Kletzing, Xiangning Chu, Louis G. Ozeke, William S. Kurth, George B. HospodarskyAbstract:We simulate the radiation belt electron flux enhancements during selected Geospace Environment Modeling (GEM) challenge events to quantitatively compare the major processes involved in relativistic electron Acceleration under different conditions. Van Allen Probes observed significant electron flux enhancement during both the storm time of 17–18 March 2013 and non–storm time of 19–20 September 2013, but the distributions of plasma waves and energetic electrons for the two events were dramatically different. During 17–18 March 2013, the SYM-H minimum reached −130 nT, intense chorus waves (peak Bw ~140 pT) occurred at 3.5 5.5, and electron fluxes at energies up to 3 MeV increased by a factor of ~5 at L > 5.5. The two electron flux enhancement events were simulated using the available wave distribution and diffusion coefficients from the GEM focus group Quantitative Assessment of Radiation Belt Modeling. By comparing the individual roles of Local electron heating and radial transport, our simulation indicates that resonant interaction with chorus waves is the dominant process that accounts for the electron flux enhancement during the storm time event particularly near the flux peak locations, while radial diffusion by ultralow-frequency waves plays a dominant role in the enhancement during the non–storm time event. Incorporation of both processes reasonably reproduces the observed location and magnitude of electron flux enhancement.
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Dependence of radiation belt simulations to assumed radial diffusion rates tested for two empirical models of radial transport
Social Work, 2017Co-Authors: Alexander Drozdov, Yuri Shprits, Nikita Aseev, Adam Kellerman, Geoffrey D. ReevesAbstract:Radial diffusion is one of the dominant physical mechanisms that drives Acceleration and loss of the radiation belt electrons, which makes it very important for nowcasting and forecasting space weather models. We investigate the sensitivity of the two parameterizations of the radial diffusion of Brautigam and Albert [2000] and Ozeke et al. [2014] on long-term radiation belt modeling using the Versatile Electron Radiation Belt (VERB). Following Brautigam and Albert [2000] and Ozeke et al. [2014], we first perform 1-D radial diffusion simulations. Comparison of the simulation results with observations shows that the difference between simulations with either radial diffusion parameterization is small. To take into account effects of Local Acceleration and loss, we perform 3-D simulations, including pitch-angle, energy and mixed diffusion. We found that the results of 3-D simulations are even less sensitive to the choice of parameterization of radial diffusion rates than the results of 1-D simulations at various energies (from 0.59 to 1.80 MeV). This result demonstrates that the inclusion of Local Acceleration and pitch-angle diffusion can provide a negative feedback effect, such that the result is largely indistinguishable simulations conducted with different radial diffusion parameterizations. We also perform a number of sensitivity tests by multiplying radial diffusion rates by constant factors and show that such an approach leads to unrealistic predictions of radiation belt dynamics.
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Radiation belt electron Acceleration by chorus waves during the 17 March 2013 storm
Journal of Geophysical Research, 2014Co-Authors: Richard M. Thorne, Jacob Bortnik, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Shrikanth G. Kanekal, Janet C. GreenAbstract:Local Acceleration driven by whistler-mode chorus waves is fundamentally important for accelerating seed electron populations to highly relativistic energies in the outer radiation belt. In this study, we quantitatively evaluate chorus-driven electron Acceleration during the 17 March 2013 storm, when the Van Allen Probes observed very rapid electron Acceleration up to several MeV within ~12 hours. A clear radial peak in electron phase space density (PSD) observed near L* ~4 indicates that an internal Local Acceleration process was operating. We construct the global distribution of chorus wave intensity from the low-altitude electron measurements made by multiple Polar Orbiting Environmental Satellites (POES) satellites over a broad region, which is ultimately used to simulate the radiation belt electron dynamics driven by chorus waves. Our simulation results show remarkable agreement in magnitude, timing, energy dependence, and pitch angle distribution with the observed electron PSD near its peak location. However, radial diffusion and other loss processes may be required to explain the differences between the observation and simulation at other locations away from the PSD peak. Our simulation results, together with previous studies, suggest that Local Acceleration by chorus waves is a robust and ubiquitous process and plays a critical role in accelerating injected seed electrons with convective energies (~100 keV) to highly relativistic energies (several MeV).
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Rapid Local Acceleration of relativistic radiation-belt electrons by magnetospheric chorus
Nature, 2013Co-Authors: Richard M. Thorne, Jacob Bortnik, Lunjin Chen, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Michael G. HendersonAbstract:High-resolution measurements of electrons obtained by satellite during the geomagnetic storm of 9 October 2012 together with a data-driven global wave model are analysed to show that scattering by a magnetospheric electromagnetic emission, known as ‘chorus’, can explain the temporal evolution of the observed increase in relativistic electron flux. A magnetic storm that occurred on 9 October 2012 has been analysed in detail using the array of instruments onboard NASA's two Van Allen probes, launched in August 2012 to study Earth's magnetosphere, including the Van Allen radiation belt. The nature of the force that accelerates electrons trapped in the radiation belts has been a topic of much debate centering on whether the electrons are accelerated Locally or by radial diffusive transport between weak and strong magnetic fields. Initial results had favoured a Local mechanism and now Richard Thorne et al. report high-resolution electron observations from Van Allen probe A, together with modelling studies that identify the likely source of accelerating energy as chorus scattering, an effect caused Locally by structured wave formations. This powerful Local Acceleration is also likely to be a factor around Jupiter, Saturn and other bodies with significant magnetic fields. Recent analysis of satellite data obtained during the 9 October 2012 geomagnetic storm identified the development of peaks in electron phase space density1, which are compelling evidence for Local electron Acceleration in the heart of the outer radiation belt2,3, but are inconsistent with Acceleration by inward radial diffusive transport4,5. 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 Acceleration6,7,8,9,10, 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 observations11 obtained during the 9 October storm and demonstrate, using a two-dimensional simulation performed with a recently developed time-varying data-driven model12, 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.
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rapid Local Acceleration of relativistic radiation belt electrons by magnetospheric chorus
Nature, 2013Co-Authors: Richard M. Thorne, Jacob Bortnik, W. Li, Lunjin Chen, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Michael G. Henderson, Binbin Ni, Craig KletzingAbstract:High-resolution measurements of electrons obtained by satellite during the geomagnetic storm of 9 October 2012 together with a data-driven global wave model are analysed to show that scattering by a magnetospheric electromagnetic emission, known as ‘chorus’, can explain the temporal evolution of the observed increase in relativistic electron flux.
Craig Kletzing - One of the best experts on this subject based on the ideXlab platform.
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Quantitative Evaluation of Radial Diffusion and Local Acceleration Processes During GEM Challenge Events
Journal of Geophysical Research, 2018Co-Authors: Jacob Bortnik, Richard M. Thorne, Geoffrey D. Reeves, Craig Kletzing, Xiangning Chu, Louis G. Ozeke, William S. Kurth, George B. HospodarskyAbstract:We simulate the radiation belt electron flux enhancements during selected Geospace Environment Modeling (GEM) challenge events to quantitatively compare the major processes involved in relativistic electron Acceleration under different conditions. Van Allen Probes observed significant electron flux enhancement during both the storm time of 17–18 March 2013 and non–storm time of 19–20 September 2013, but the distributions of plasma waves and energetic electrons for the two events were dramatically different. During 17–18 March 2013, the SYM-H minimum reached −130 nT, intense chorus waves (peak Bw ~140 pT) occurred at 3.5 5.5, and electron fluxes at energies up to 3 MeV increased by a factor of ~5 at L > 5.5. The two electron flux enhancement events were simulated using the available wave distribution and diffusion coefficients from the GEM focus group Quantitative Assessment of Radiation Belt Modeling. By comparing the individual roles of Local electron heating and radial transport, our simulation indicates that resonant interaction with chorus waves is the dominant process that accounts for the electron flux enhancement during the storm time event particularly near the flux peak locations, while radial diffusion by ultralow-frequency waves plays a dominant role in the enhancement during the non–storm time event. Incorporation of both processes reasonably reproduces the observed location and magnitude of electron flux enhancement.
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The complex nature of storm‐time ion dynamics: Transport and Local Acceleration
Geophysical Research Letters, 2016Co-Authors: Michael H. Denton, Harlan E. Spence, Michael G. Henderson, R. H. W. Friedel, Herbert O. Funsten, G. E. Reeves, Michelle F. Thomsen, Brian A. Larsen, Ruth M. Skoug, Craig KletzingAbstract:Data from the Van Allen Probes Helium, Oxygen, Proton, Electron (HOPE) spectrometers reveal hitherto unresolved spatial structure and dynamics in ion populations. Complex regions of O+ dominance, at energies from a few eV to >10 keV, are observed throughout the magnetosphere. Isolated regions on the dayside that are rich in energetic O+ might easily be interpreted as strong energization of ionospheric plasma. We demonstrate, however, that both the energy spectrum and the limited MLT extent of these features can be explained by energy-dependent drift of particles injected on the night side 24 hours earlier. Particle tracing simulations show that the energetic O+ can originate in the magnetotail, not in the ionosphere. Enhanced wave activity is co-located with the heavy-ion rich plasma and we further conclude that the waves were not a source of free energy for accelerating ionospheric plasma but rather the consequence of the arrival of substorm-injected plasma.
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Nonstorm time dynamics of electron radiation belts observed by the Van Allen Probes
Geophysical Research Letters, 2014Co-Authors: Fuliang Xiao, Huinan Zheng, Hui Zhu, Min Zhang, Chao Shen, Yuming Wang, Shui Wang, Craig KletzingAbstract:Storm time electron radiation belt dynamics have been widely investigated for many years. Here we present a rarely reported nonstorm time event of electron radiation belt evolution observed by the Van Allen Probes during 21-24 February 2013. Within 2 days, a new belt centering around L=5.8 formed and gradually merged with the original outer belt, with the enhancement of relativistic electron fluxes by a factor of up to 50. Strong chorus waves (with power spectral density up to 10(-4)nT(2)/Hz) occurred in the region L>5. Taking into account the Local Acceleration driven by these chorus waves, the two-dimensional STEERB can approximately reproduce the observed energy spectrums at the center of the new belt. These results clearly illustrate the complexity of electron radiation belt behaviors and the importance of chorus-driven Local Acceleration even during the nonstorm times. Key Points A rarely reported nonstorm time event of RB reformation observed by RBSP Formation of a new belt near the outer boundary of the original outer belt Importance of chorus-driven Local Acceleration: observation and simulation
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rapid Local Acceleration of relativistic radiation belt electrons by magnetospheric chorus
Nature, 2013Co-Authors: Richard M. Thorne, Jacob Bortnik, W. Li, Lunjin Chen, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Michael G. Henderson, Binbin Ni, Craig KletzingAbstract:High-resolution measurements of electrons obtained by satellite during the geomagnetic storm of 9 October 2012 together with a data-driven global wave model are analysed to show that scattering by a magnetospheric electromagnetic emission, known as ‘chorus’, can explain the temporal evolution of the observed increase in relativistic electron flux.
Yong-chae Chung - One of the best experts on this subject based on the ideXlab platform.
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Asymmetric surface intermixing during thin-film growth in the Co–Al system: Role of Local Acceleration of the deposited atoms
Acta Materialia, 2008Co-Authors: Sang Pil Kim, Seung-cheol Lee, Kwang-ryeol Lee, Yong-chae ChungAbstract:Abstract Surface intermixing behavior during thin-film deposition in the Co–Al system was investigated on the atomic scale by three-dimensional classical molecular dynamics simulation. Asymmetry of the surface intermixing was observed: Al deposition on a Co substrate resulted in an Al thin-film with an atomically sharp interface, while a Co thin-film deposited on an Al substrate had an interfacial intermixing layer of B2 structure. This phenomenon is discussed in terms of the kinetics of atomic intermixing on the surface. A kinetic criterion for the atomic intermixing is whether the increased kinetic energy of the deposited atom near the surface is larger than the energy barrier to atomic intermixing on the surface. Local Acceleration of the deposited atoms near the surface provides an explanation of the puzzling phenomenon of the significant intermixing under low-energy deposition conditions such as thermal evaporation or molecular beam epitaxy.
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Local Acceleration Effects of Adatom at the Vicinity on the Surface: Case of Co Nano Thin-Films on Al Surface
Key Engineering Materials, 2006Co-Authors: Seung-cheol Lee, Sang Pil Kim, Kwang Real Lee, Yong-chae ChungAbstract:The Local Acceleration effects, which are peculiar phenomena during atomic scale deposition process, were investigated byMolecular Dynamics (MD) simulation. The values of Local Acceleration were distributed widely for various surface orientations. Deposited atoms were accelerated along the potential energy surface, and accelerated values were evidently dependent on the Local configuration of the surface. In contrast, the Local Acceleration became negligibly small for clusters consisting of many atoms.
Richard M. Thorne - One of the best experts on this subject based on the ideXlab platform.
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Quantitative Evaluation of Radial Diffusion and Local Acceleration Processes During GEM Challenge Events
Journal of Geophysical Research, 2018Co-Authors: Jacob Bortnik, Richard M. Thorne, Geoffrey D. Reeves, Craig Kletzing, Xiangning Chu, Louis G. Ozeke, William S. Kurth, George B. HospodarskyAbstract:We simulate the radiation belt electron flux enhancements during selected Geospace Environment Modeling (GEM) challenge events to quantitatively compare the major processes involved in relativistic electron Acceleration under different conditions. Van Allen Probes observed significant electron flux enhancement during both the storm time of 17–18 March 2013 and non–storm time of 19–20 September 2013, but the distributions of plasma waves and energetic electrons for the two events were dramatically different. During 17–18 March 2013, the SYM-H minimum reached −130 nT, intense chorus waves (peak Bw ~140 pT) occurred at 3.5 5.5, and electron fluxes at energies up to 3 MeV increased by a factor of ~5 at L > 5.5. The two electron flux enhancement events were simulated using the available wave distribution and diffusion coefficients from the GEM focus group Quantitative Assessment of Radiation Belt Modeling. By comparing the individual roles of Local electron heating and radial transport, our simulation indicates that resonant interaction with chorus waves is the dominant process that accounts for the electron flux enhancement during the storm time event particularly near the flux peak locations, while radial diffusion by ultralow-frequency waves plays a dominant role in the enhancement during the non–storm time event. Incorporation of both processes reasonably reproduces the observed location and magnitude of electron flux enhancement.
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Radiation belt electron Acceleration by chorus waves during the 17 March 2013 storm
2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014Co-Authors: Richard M. Thorne, Jacob BortnikAbstract:Local Acceleration driven by whistler-mode chorus waves is suggested to be fundamentally important for accelerating seed electron population to ultra-relativistic energies in the outer radiation belt. In this study, we quantitatively evaluate chorus-driven electron Acceleration during the 17 March 2013 storm, when Van Allen Probes observed very rapid electron Acceleration up to multi MeV within ∼15 hours. A clear peak in electron phase space density observed at L∗ ∼ 4 indicates that the internal Local Acceleration process was operating. We construct the global distribution of chorus wave intensity from the low-altitude electron measurements by multiple POES satellites over a broad L-MLT region, which is used to simulate the radiation belt electron dynamics driven by chorus waves. Our simulation results show remarkable agreement with the observed electron PSD near its peak in timing, energy dependence, and pitch angle distribution, but other loss processes and radial diffusion may be required to explain the differences in observation and simulation at other locations away from the PSD peak. Our simulation results suggest that Local Acceleration by chorus waves is likely to be a robust and repetitive process and plays a critical role in accelerating radiation belt electrons from injected convective energies (∼ 100 keV) to ultra-relativistic energies (multi MeV).
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Radiation belt electron Acceleration by chorus waves during the 17 March 2013 storm
Journal of Geophysical Research, 2014Co-Authors: Richard M. Thorne, Jacob Bortnik, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Shrikanth G. Kanekal, Janet C. GreenAbstract:Local Acceleration driven by whistler-mode chorus waves is fundamentally important for accelerating seed electron populations to highly relativistic energies in the outer radiation belt. In this study, we quantitatively evaluate chorus-driven electron Acceleration during the 17 March 2013 storm, when the Van Allen Probes observed very rapid electron Acceleration up to several MeV within ~12 hours. A clear radial peak in electron phase space density (PSD) observed near L* ~4 indicates that an internal Local Acceleration process was operating. We construct the global distribution of chorus wave intensity from the low-altitude electron measurements made by multiple Polar Orbiting Environmental Satellites (POES) satellites over a broad region, which is ultimately used to simulate the radiation belt electron dynamics driven by chorus waves. Our simulation results show remarkable agreement in magnitude, timing, energy dependence, and pitch angle distribution with the observed electron PSD near its peak location. However, radial diffusion and other loss processes may be required to explain the differences between the observation and simulation at other locations away from the PSD peak. Our simulation results, together with previous studies, suggest that Local Acceleration by chorus waves is a robust and ubiquitous process and plays a critical role in accelerating injected seed electrons with convective energies (~100 keV) to highly relativistic energies (several MeV).
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Rapid Local Acceleration of relativistic radiation-belt electrons by magnetospheric chorus
Nature, 2013Co-Authors: Richard M. Thorne, Jacob Bortnik, Lunjin Chen, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Michael G. HendersonAbstract:High-resolution measurements of electrons obtained by satellite during the geomagnetic storm of 9 October 2012 together with a data-driven global wave model are analysed to show that scattering by a magnetospheric electromagnetic emission, known as ‘chorus’, can explain the temporal evolution of the observed increase in relativistic electron flux. A magnetic storm that occurred on 9 October 2012 has been analysed in detail using the array of instruments onboard NASA's two Van Allen probes, launched in August 2012 to study Earth's magnetosphere, including the Van Allen radiation belt. The nature of the force that accelerates electrons trapped in the radiation belts has been a topic of much debate centering on whether the electrons are accelerated Locally or by radial diffusive transport between weak and strong magnetic fields. Initial results had favoured a Local mechanism and now Richard Thorne et al. report high-resolution electron observations from Van Allen probe A, together with modelling studies that identify the likely source of accelerating energy as chorus scattering, an effect caused Locally by structured wave formations. This powerful Local Acceleration is also likely to be a factor around Jupiter, Saturn and other bodies with significant magnetic fields. Recent analysis of satellite data obtained during the 9 October 2012 geomagnetic storm identified the development of peaks in electron phase space density1, which are compelling evidence for Local electron Acceleration in the heart of the outer radiation belt2,3, but are inconsistent with Acceleration by inward radial diffusive transport4,5. 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 Acceleration6,7,8,9,10, 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 observations11 obtained during the 9 October storm and demonstrate, using a two-dimensional simulation performed with a recently developed time-varying data-driven model12, 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.
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rapid Local Acceleration of relativistic radiation belt electrons by magnetospheric chorus
Nature, 2013Co-Authors: Richard M. Thorne, Jacob Bortnik, W. Li, Lunjin Chen, Daniel N. Baker, Harlan E. Spence, Geoffrey D. Reeves, Michael G. Henderson, Binbin Ni, Craig KletzingAbstract:High-resolution measurements of electrons obtained by satellite during the geomagnetic storm of 9 October 2012 together with a data-driven global wave model are analysed to show that scattering by a magnetospheric electromagnetic emission, known as ‘chorus’, can explain the temporal evolution of the observed increase in relativistic electron flux.