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D N Baker - One of the best experts on this subject based on the ideXlab platform.
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rapid Outer Radiation Belt flux dropouts and fast acceleration during the march 2015 and 2013 storms the role of ultra low frequency wave transport from a dynamic Outer boundary
Journal of Geophysical Research, 2020Co-Authors: L G Ozeke, H E Spence, K R Murphy, I R Mann, S G Claudepierre, L Olifer, K Y Dufresne, S K Morley, D N BakerAbstract:We present simulations of the Outer Radiation Belt electron flux during the March 2015 and March 2013 storms using a radial diffusion model. Despite differences in Dst intensity between the two sto...
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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, I R Mann, David G Sibeck, A J Boyd, C Forsyth, S G Claudepierre, 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, S G Kanekal, V A Pinto, 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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the effects of magnetospheric processes on relativistic electron dynamics in the earth s Outer Radiation Belt
Journal of Geophysical Research, 2017Co-Authors: J C Zhang, G D Reeves, Zhenpeng Su, D N Baker, H E Spence, Chaoli Tang, Yiyun Wang, Binbin Ni, H O FunstenAbstract:Using the electron phase space density (PSD) data measured by Van Allen Probe A from January 2013 to April 2015, we investigate the effects of magnetospheric processes on relativistic electron dynamics in the Earth's Outer Radiation Belt during 50 geomagnetic storms. A statistical study shows that the maximum electron PSDs for various μ (μ = 630, 1096, 2290, and 3311 MeV/G) at L*~4.0 after the storm peak have good correlations with storm intensity (cc~0.70). This suggests that the occurrence and magnitude of geomagnetic storms are necessary for relativistic electron enhancements at the inner edge of the Outer Radiation Belt (L* = 4.0). For moderate or weak storm events (SYM-Hmin > ~−100 nT) with weak substorm activity (AEmax 0.77). For storm events with intense substorms after the storm peak, relativistic electron enhancements at L* = 4.5 and 5.0 are observed. This shows that intense substorms during the storm recovery phase are crucial to relativistic electron enhancements in the heart of the Outer Radiation Belt. Our statistics study suggests that magnetospheric processes during geomagnetic storms have a significant effect on relativistic electron dynamics.
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roles of whistler mode waves and magnetosonic waves in changing the Outer Radiation Belt and the slot region
Journal of Geophysical Research, 2017Co-Authors: L Y Li, G D Reeves, D N Baker, J Yu, J Y Yang, X Li, H E SpenceAbstract:Using the Van Allen Probe long-term (2013 – 2015) observations and quasi-linear simulations of wave-particle interactions, we examine the combined or competing effects of whistler-mode waves (chorus or hiss) and magnetosonic (MS) waves on energetic ( 0.5 MeV) electrons inside and outside the plasmasphere. Although whistler-mode chorus waves and MS waves can singly or jointly accelerate electrons from the hundreds of keV energy to the MeV energy in the low-density trough, most of the relativistic electron enhancement events are best correlated with the chorus wave emissions outside the plasmapause. Inside the plasmasphere, intense plasmaspheric hiss can cause the net loss of relativistic electrons via persistent pitch angle scattering, regardless of whether MS waves were present or not. The intense hiss waves not only create the energy-dependent electron slot region, but also remove a lot of the Outer Radiation Belt electrons when the expanding dayside plasmasphere frequently covers the Outer zone. Since whistler-mode waves (chorus or hiss) can resonate with more electrons than MS waves, they play dominant roles in changing the Outer Radiation Belt and the slot region. However, MS waves can accelerate the energetic electrons below 400 keV and weaken their loss inside the plasmapause. Thus, MS waves and plasmaspheric hiss generate different competing effects on energetic and relativistic electrons in the high-density plasmasphere.
H E Spence - One of the best experts on this subject based on the ideXlab platform.
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rapid Outer Radiation Belt flux dropouts and fast acceleration during the march 2015 and 2013 storms the role of ultra low frequency wave transport from a dynamic Outer boundary
Journal of Geophysical Research, 2020Co-Authors: L G Ozeke, H E Spence, K R Murphy, I R Mann, S G Claudepierre, L Olifer, K Y Dufresne, S K Morley, D N BakerAbstract:We present simulations of the Outer Radiation Belt electron flux during the March 2015 and March 2013 storms using a radial diffusion model. Despite differences in Dst intensity between the two sto...
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the effects of magnetospheric processes on relativistic electron dynamics in the earth s Outer Radiation Belt
Journal of Geophysical Research, 2017Co-Authors: J C Zhang, G D Reeves, Zhenpeng Su, D N Baker, H E Spence, Chaoli Tang, Yiyun Wang, Binbin Ni, H O FunstenAbstract:Using the electron phase space density (PSD) data measured by Van Allen Probe A from January 2013 to April 2015, we investigate the effects of magnetospheric processes on relativistic electron dynamics in the Earth's Outer Radiation Belt during 50 geomagnetic storms. A statistical study shows that the maximum electron PSDs for various μ (μ = 630, 1096, 2290, and 3311 MeV/G) at L*~4.0 after the storm peak have good correlations with storm intensity (cc~0.70). This suggests that the occurrence and magnitude of geomagnetic storms are necessary for relativistic electron enhancements at the inner edge of the Outer Radiation Belt (L* = 4.0). For moderate or weak storm events (SYM-Hmin > ~−100 nT) with weak substorm activity (AEmax 0.77). For storm events with intense substorms after the storm peak, relativistic electron enhancements at L* = 4.5 and 5.0 are observed. This shows that intense substorms during the storm recovery phase are crucial to relativistic electron enhancements in the heart of the Outer Radiation Belt. Our statistics study suggests that magnetospheric processes during geomagnetic storms have a significant effect on relativistic electron dynamics.
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roles of whistler mode waves and magnetosonic waves in changing the Outer Radiation Belt and the slot region
Journal of Geophysical Research, 2017Co-Authors: L Y Li, G D Reeves, D N Baker, J Yu, J Y Yang, X Li, H E SpenceAbstract:Using the Van Allen Probe long-term (2013 – 2015) observations and quasi-linear simulations of wave-particle interactions, we examine the combined or competing effects of whistler-mode waves (chorus or hiss) and magnetosonic (MS) waves on energetic ( 0.5 MeV) electrons inside and outside the plasmasphere. Although whistler-mode chorus waves and MS waves can singly or jointly accelerate electrons from the hundreds of keV energy to the MeV energy in the low-density trough, most of the relativistic electron enhancement events are best correlated with the chorus wave emissions outside the plasmapause. Inside the plasmasphere, intense plasmaspheric hiss can cause the net loss of relativistic electrons via persistent pitch angle scattering, regardless of whether MS waves were present or not. The intense hiss waves not only create the energy-dependent electron slot region, but also remove a lot of the Outer Radiation Belt electrons when the expanding dayside plasmasphere frequently covers the Outer zone. Since whistler-mode waves (chorus or hiss) can resonate with more electrons than MS waves, they play dominant roles in changing the Outer Radiation Belt and the slot region. However, MS waves can accelerate the energetic electrons below 400 keV and weaken their loss inside the plasmapause. Thus, MS waves and plasmaspheric hiss generate different competing effects on energetic and relativistic electrons in the high-density plasmasphere.
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prompt enhancement of the earth s Outer Radiation Belt due to substorm electron injections
Journal of Geophysical Research, 2016Co-Authors: C L Tang, J C Zhang, G D Reeves, Zhenpeng Su, D N Baker, H E Spence, H O Funsten, J B Blake, J R WygantAbstract:We present multipoint simultaneous observations of the near-Earth magnetotail and Outer Radiation Belt during the substorm electron injection event on 16 August 2013. Time History of Events and Macroscale Interactions during Substorms A in the near-Earth magnetotail observed flux-enhanced electrons of 300 keV during the magnetic field dipolarization. Geosynchronous orbit satellites also observed the intensive electron injections. Located in the Outer Radiation Belt, RBSP-A observed enhancements of MeV electrons accompanied by substorm dipolarization. The phase space density (PSD) of MeV electrons at L*~5.4 increased by 1 order of magnitude in 1 h, resulting in a local PSD peak of MeV electrons, which was caused by the direct effect of substorm injections. Enhanced MeV electrons in the heart of the Outer Radiation Belt were also detected within 2 h, which may be associated with intensive substorm electron injections and subsequent local acceleration by chorus waves. Multipoint observations have shown that substorm electron injections not only can be the external source of MeV electrons at the Outer edge of the Outer Radiation Belt (L*~5.4) but also can provide the intensive seed populations in the Outer Radiation Belt. These initial higher-energy electrons from injection can reach relativistic energy much faster. The observations also provide evidence that enhanced substorm electron injections can explain rapid enhancements of MeV electrons in the Outer Radiation Belt.
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earth s magnetosphere and Outer Radiation Belt under sub alfvenic solar wind
Nature Communications, 2016Co-Authors: N Lugaz, H E Spence, C J Farrugia, Chialin Huang, Reka M Winslow, N A SchwadronAbstract:The interaction between Earth’s magnetic field and the solar wind results in the formation of a collisionless bow shock 60,000–100,000 km upstream of our planet, as long as the solar wind fast magnetosonic Mach (hereafter Mach) number exceeds unity. Here, we present one of those extremely rare instances, when the solar wind Mach number reached steady values <1 for several hours on 17 January 2013. Simultaneous measurements by more than ten spacecraft in the near-Earth environment reveal the evanescence of the bow shock, the sunward motion of the magnetopause and the extremely rapid and intense loss of electrons in the Outer Radiation Belt. This study allows us to directly observe the state of the inner magnetosphere, including the Radiation Belts during a type of solar wind-magnetosphere coupling which is unusual for planets in our solar system but may be common for close-in extrasolar planets. The interaction between the Earth’s magnetic field and the solar wind results in the formation of a collisionless bow shock. Here, the authors study an even in which the solar wind Mach number remained steadily below one, leading to the evanescence of the bow shock and loss of electrons in the Outer Belts.
D L Turner - 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, I R Mann, David G Sibeck, A J Boyd, C Forsyth, S G Claudepierre, 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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competing source and loss mechanisms due to wave particle interactions in earth s Outer Radiation Belt during the 30 september to 3 october 2012 geomagnetic storm
Journal of Geophysical Research, 2014Co-Authors: D L Turner, Vassilis Angelopoulos, G D Reeves, Binbin Ni, W Li, S K Morley, J Bortnik, R M Thorne, M G Henderson, M UsanovaAbstract:Drastic variations of Earth's Outer Radiation Belt electrons ultimately result from various competing source, loss, and transport processes, to which wave-particle interactions are critically important. Using 15 spacecraft including NASA's Van Allen Probes, THEMIS, and SAMPEX missions and NOAA's GOES and POES constellations, we investigated the evolution of the Outer Belt during the strong geomagnetic storm of 30 September to 3 October 2012. This storm's main phase dropout exhibited enhanced losses to the atmosphere at L* 1 MeV electrons and energetic protons, SAMPEX >1 MeV electrons, and ground observations of band-limited Pc1-2 wave activity, we show that this sudden loss was consistent with pitch angle scattering by electromagnetic ion cyclotron waves in the dusk magnetic local time sector at 3 300 nT, and energetic electron injections and whistler-mode chorus waves were observed throughout the inner magnetosphere for >12 h. After this period, Bz turned northward, and injections, chorus activity, and enhancements in PSD ceased. Overall, the Outer Belt was depleted by this storm. From the unprecedented level of observations available, we show direct evidence of the competitive nature of different wave-particle interactions controlling relativistic electron fluxes in the Outer Radiation Belt.
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a nonstorm time enhancement of relativistic electrons in the Outer Radiation Belt
Geophysical Research Letters, 2014Co-Authors: Q Schiller, D L Turner, X Li, L W Blum, W Tu, J B BlakeAbstract:[1] Despite the lack of a geomagnetic storm (based on the Dst index), relativistic electron fluxes were enhanced over 2.5 orders of magnitude in the Outer Radiation Belt in 13 h on 13–14 January 2013. The unusual enhancement was observed by Magnetic Electron Ion Spectrometer (MagEIS), onboard the Van Allen Probes; Relativistic Electron and Proton Telescope Integrated Little Experiment, onboard the Colorado Student Space Weather Experiment; and Solid State Telescope, onboard Time History of Events and Macroscale Interactions during Substorms (THEMIS). Analyses of MagEIS phase space density (PSD) profiles show a positive outward radial gradient from 4 < L < 5.5. However, THEMIS observations show a peak in PSD outside of the Van Allen Probes' apogee, which suggest a very interesting scenario: wave-particle interactions causing a PSD peak at ~ L* = 5.5 from where the electrons are then rapidly transported radially inward. This letter demonstrates, for the first time in detail, that geomagnetic storms are not necessary for causing dramatic enhancements in the Outer Radiation Belt.
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significant loss of energetic electrons at the heart of the Outer Radiation Belt during weak magnetic storms
Journal of Geophysical Research, 2013Co-Authors: Junga Hwang, Daekyu Shin, M Y Park, D L TurnerAbstract:[1] For various reasons, the Earth's Outer Radiation Belt often exhibits dramatic and sudden increases or decreases in the observed particle flux. In this paper, we report three dropout events of energetic electrons observed by multiple spacecraft while traveling across the Outer Radiation Belt. The three events were first identified based on observations of a significant dropout in the >2 MeV electron flux at geosynchronous orbit. Subsequently, for each event, we analyzed the energetic electron data obtained near the magnetic equator by THEMIS spacecraft to determine the responses of the entire Outer Radiation Belt. Our analysis is mainly based on the electron fluxes measured at energies of 52 keV, 203 keV, and 719 keV, and on the phase space densities estimated for the first adiabatic invariant μ values of 100 MeV/G, 200 MeV/G, and 300 MeV/G. The main shared feature among the three events is that while, for the lowest energy, sources from the convection and/or particle injections of plasma sheet electrons dominate over losses, the higher energies exhibit a dramatic dropout effect that penetrates deeply into L ~ 4.5 – 5. In terms of the phase space density, a similar dropout effect is clearly seen for the μ values of 200 MeV/G and 300 MeV/G, while the convection effect and/or injections dominates for μ = 100 MeV/G. What is astonishing about this dropout phenomenon is that the three events are all associated with only very weak magnetic storms with a SYM-H minimum of -40 nT or larger. This implies that a significant loss of electrons deep inside the Outer Radiation Belt can occur even during a very weak magnetic storm. Low-altitude observations of electrons by NOAA POES satellites indicate no significant atmospheric precipitation due to strong diffusion. Our simulations with various conditions suggest that radial diffusion effect in combination with the magnetopause shadowing are responsible for the observed dropouts to a large extent for all of the three events, although the contribution by the weak atmospheric precipitation that might have been missed by the NOAA POES observations can be non-negligible.
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long term loss and re formation of the Outer Radiation Belt
Journal of Geophysical Research, 2013Co-Authors: Daekyu Shin, D L Turner, Junga Hwang, M Y ParkAbstract:[1] The Earth's Outer Radiation Belt is known to vary often and significantly on various time scales. In this study, we have used the data of various instruments onboard the THEMIS spacecraft to study long-term changes of the Outer Radiation Belt electrons around the year 2009. We find that the entire Outer Belt became extremely weak for nearly a year and was practically lost a few times, each time lasting ~20 days up to ~2 months, before eventually re-forming. This was revealed at a wide energy range from several tens of keV to up to 719 keV, which was covered by the THEMIS spacecraft measurements. The loss of the Outer Belt was associated with extremely weak solar wind conditions, i.e., low interplanetary magnetic field magnitude and slow solar wind speed. In particular, this set greatly reduced magnetospheric convection and/or injections for a prolonged time interval, which led to a large expansion of the plasmasphere, even beyond geosynchronous altitude and thus invading the majority of the typical Outer Belt territory for the same prolonged time interval. Consequently, preexisting electrons inside the plasmasphere had enough time to be lost into the atmosphere gradually over a time scale of several days without being supplied with fresh electrons from the plasma sheet under the same reduced convection and/or injections. Plasmaspheric hiss waves with an amplitude of up to a few tens of pT persisted to exist during the gradual decay periods, implying that they are likely responsible for the continual loss of the electrons inside the plasmasphere. A complete re-formation of the Outer Belt to full intensity was then realized over an interval of a few months. During the re-formation process, the magnetospheric convection and/or injections increased, which led to a gradual increase of whistler chorus wave activity, contraction of the plasmasphere, and supply of the plasma sheet electrons at high L shells. This set first an outward increasing profile of the phase space density, which eventually developed into a profile with a peak at low L of ~5 over a time scale of 1–2 days. In this latter stage, a local acceleration at low L shells is found to be clearly needed although the radial diffusion process can contribute to some extent, in particular, for particles with a low first adiabatic invariant value.
G D Reeves - One of the best experts on this subject based on the ideXlab platform.
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the effects of magnetospheric processes on relativistic electron dynamics in the earth s Outer Radiation Belt
Journal of Geophysical Research, 2017Co-Authors: J C Zhang, G D Reeves, Zhenpeng Su, D N Baker, H E Spence, Chaoli Tang, Yiyun Wang, Binbin Ni, H O FunstenAbstract:Using the electron phase space density (PSD) data measured by Van Allen Probe A from January 2013 to April 2015, we investigate the effects of magnetospheric processes on relativistic electron dynamics in the Earth's Outer Radiation Belt during 50 geomagnetic storms. A statistical study shows that the maximum electron PSDs for various μ (μ = 630, 1096, 2290, and 3311 MeV/G) at L*~4.0 after the storm peak have good correlations with storm intensity (cc~0.70). This suggests that the occurrence and magnitude of geomagnetic storms are necessary for relativistic electron enhancements at the inner edge of the Outer Radiation Belt (L* = 4.0). For moderate or weak storm events (SYM-Hmin > ~−100 nT) with weak substorm activity (AEmax 0.77). For storm events with intense substorms after the storm peak, relativistic electron enhancements at L* = 4.5 and 5.0 are observed. This shows that intense substorms during the storm recovery phase are crucial to relativistic electron enhancements in the heart of the Outer Radiation Belt. Our statistics study suggests that magnetospheric processes during geomagnetic storms have a significant effect on relativistic electron dynamics.
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roles of whistler mode waves and magnetosonic waves in changing the Outer Radiation Belt and the slot region
Journal of Geophysical Research, 2017Co-Authors: L Y Li, G D Reeves, D N Baker, J Yu, J Y Yang, X Li, H E SpenceAbstract:Using the Van Allen Probe long-term (2013 – 2015) observations and quasi-linear simulations of wave-particle interactions, we examine the combined or competing effects of whistler-mode waves (chorus or hiss) and magnetosonic (MS) waves on energetic ( 0.5 MeV) electrons inside and outside the plasmasphere. Although whistler-mode chorus waves and MS waves can singly or jointly accelerate electrons from the hundreds of keV energy to the MeV energy in the low-density trough, most of the relativistic electron enhancement events are best correlated with the chorus wave emissions outside the plasmapause. Inside the plasmasphere, intense plasmaspheric hiss can cause the net loss of relativistic electrons via persistent pitch angle scattering, regardless of whether MS waves were present or not. The intense hiss waves not only create the energy-dependent electron slot region, but also remove a lot of the Outer Radiation Belt electrons when the expanding dayside plasmasphere frequently covers the Outer zone. Since whistler-mode waves (chorus or hiss) can resonate with more electrons than MS waves, they play dominant roles in changing the Outer Radiation Belt and the slot region. However, MS waves can accelerate the energetic electrons below 400 keV and weaken their loss inside the plasmapause. Thus, MS waves and plasmaspheric hiss generate different competing effects on energetic and relativistic electrons in the high-density plasmasphere.
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prompt enhancement of the earth s Outer Radiation Belt due to substorm electron injections
Journal of Geophysical Research, 2016Co-Authors: C L Tang, J C Zhang, G D Reeves, Zhenpeng Su, D N Baker, H E Spence, H O Funsten, J B Blake, J R WygantAbstract:We present multipoint simultaneous observations of the near-Earth magnetotail and Outer Radiation Belt during the substorm electron injection event on 16 August 2013. Time History of Events and Macroscale Interactions during Substorms A in the near-Earth magnetotail observed flux-enhanced electrons of 300 keV during the magnetic field dipolarization. Geosynchronous orbit satellites also observed the intensive electron injections. Located in the Outer Radiation Belt, RBSP-A observed enhancements of MeV electrons accompanied by substorm dipolarization. The phase space density (PSD) of MeV electrons at L*~5.4 increased by 1 order of magnitude in 1 h, resulting in a local PSD peak of MeV electrons, which was caused by the direct effect of substorm injections. Enhanced MeV electrons in the heart of the Outer Radiation Belt were also detected within 2 h, which may be associated with intensive substorm electron injections and subsequent local acceleration by chorus waves. Multipoint observations have shown that substorm electron injections not only can be the external source of MeV electrons at the Outer edge of the Outer Radiation Belt (L*~5.4) but also can provide the intensive seed populations in the Outer Radiation Belt. These initial higher-energy electrons from injection can reach relativistic energy much faster. The observations also provide evidence that enhanced substorm electron injections can explain rapid enhancements of MeV electrons in the Outer Radiation Belt.
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competing source and loss mechanisms due to wave particle interactions in earth s Outer Radiation Belt during the 30 september to 3 october 2012 geomagnetic storm
Journal of Geophysical Research, 2014Co-Authors: D L Turner, Vassilis Angelopoulos, G D Reeves, Binbin Ni, W Li, S K Morley, J Bortnik, R M Thorne, M G Henderson, M UsanovaAbstract:Drastic variations of Earth's Outer Radiation Belt electrons ultimately result from various competing source, loss, and transport processes, to which wave-particle interactions are critically important. Using 15 spacecraft including NASA's Van Allen Probes, THEMIS, and SAMPEX missions and NOAA's GOES and POES constellations, we investigated the evolution of the Outer Belt during the strong geomagnetic storm of 30 September to 3 October 2012. This storm's main phase dropout exhibited enhanced losses to the atmosphere at L* 1 MeV electrons and energetic protons, SAMPEX >1 MeV electrons, and ground observations of band-limited Pc1-2 wave activity, we show that this sudden loss was consistent with pitch angle scattering by electromagnetic ion cyclotron waves in the dusk magnetic local time sector at 3 300 nT, and energetic electron injections and whistler-mode chorus waves were observed throughout the inner magnetosphere for >12 h. After this period, Bz turned northward, and injections, chorus activity, and enhancements in PSD ceased. Overall, the Outer Belt was depleted by this storm. From the unprecedented level of observations available, we show direct evidence of the competitive nature of different wave-particle interactions controlling relativistic electron fluxes in the Outer Radiation Belt.
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are energetic electrons in the solar wind the source of the Outer Radiation Belt
Geophysical Research Letters, 1997Co-Authors: X Li, D E Larson, G D Reeves, D N Baker, M Temerin, M D Looper, S G Kanekal, R A MewaldtAbstract:Using data from WIND, SAMPEX (Solar Anomalous, and Magnetospheric Particle Explorer), and the Los Alamos National Laboratory (LANL) sensors onboard geostationary satellites, we investigate the correlation of energetic electrons in the 20–200 keV range in the solar wind and of high speed solar wind streams with relativistic electrons in the magnetosphere to determine whether energetic electrons in the solar wind are the source of the Outer relativistic electron Radiation Belt. Though there is some correlation between energetic electron enhancements in the solar wind and enhancements in the Outer Radiation Belt, the phase space density of 20–200 keV electrons in the solar wind is not adequate to supply the Outer Radiation Belt electrons. Although lower energy electrons in the solar wind could be a seed population of the Outer Radiation Belt, such lower energy electrons cannot achieve relativistic energies through the normal process of radial transport which conserves the first adiabatic invariant. Thus additional internal acceleration processes are required within the magnetosphere to produce the Outer Radiation Belt. High speed solar wind streams are well correlated with increased magnetic activity and with increased fluxes in the Outer Radiation Belt. The maximum correlation between the high speed streams and the Radiation Belt flux occurs with an increasing time delay for higher energies and and lower L values. We conclude that acceleration processes within the magnetosphere which are well correlated with high speed solar wind streams are responsible for the Outer Radiation Belt electrons.
Yoshizumi Miyoshi - One of the best experts on this subject based on the ideXlab platform.
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high speed solar wind with southward interplanetary magnetic field causes relativistic electron flux enhancement of the Outer Radiation Belt via enhanced condition of whistler waves
Geophysical Research Letters, 2013Co-Authors: Yoshizumi Miyoshi, Yoshiya Kasahara, Ryuho Kataoka, Atsushi Kumamoto, T Nagai, M F ThomsenAbstract:[1] Relativistic electron flux in the Outer Radiation Belt tends to increase during the high-speed solar wind stream (HSS) events. However, HSS events do not always cause large flux enhancement. To determine the HSS events that cause such enhancement and the mechanisms that are responsible for accelerating the electrons, we analyzed long-term plasma data sets, for periods longer than one solar cycle. We demonstrate that during HSS events with the southward interplanetary magnetic field (IMF)-dominant HSS (SBz-HSS), relativistic electrons are accelerated by whistler mode waves; however, during HSS events with the northward IMF-dominant HSS, this acceleration mechanism is not effective. The differences in the responses of the Outer Radiation Belt flux variations are caused by the differences in the whistler mode wave–electron interactions associated with a series of substorms. During SBz-HSS events, hot electron injections occur and the thermal plasma density decreases due to the shrinkage of the plasmapause, causing large flux enhancement of relativistic electrons through whistler mode wave excitation. These results explain why large flux enhancement of relativistic electrons tends to occur during SBz-HSS events.
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High‐speed solar wind with southward interplanetary magnetic field causes relativistic electron flux enhancement of the Outer Radiation Belt via enhanced condition of whistler waves
Geophysical Research Letters, 2013Co-Authors: Yoshizumi Miyoshi, T Nagai, Yoshiya Kasahara, Ryuho Kataoka, Atsushi Kumamoto, M F ThomsenAbstract:[1] Relativistic electron flux in the Outer Radiation Belt tends to increase during the high-speed solar wind stream (HSS) events. However, HSS events do not always cause large flux enhancement. To determine the HSS events that cause such enhancement and the mechanisms that are responsible for accelerating the electrons, we analyzed long-term plasma data sets, for periods longer than one solar cycle. We demonstrate that during HSS events with the southward interplanetary magnetic field (IMF)-dominant HSS (SBz-HSS), relativistic electrons are accelerated by whistler mode waves; however, during HSS events with the northward IMF-dominant HSS, this acceleration mechanism is not effective. The differences in the responses of the Outer Radiation Belt flux variations are caused by the differences in the whistler mode wave–electron interactions associated with a series of substorms. During SBz-HSS events, hot electron injections occur and the thermal plasma density decreases due to the shrinkage of the plasmapause, causing large flux enhancement of relativistic electrons through whistler mode wave excitation. These results explain why large flux enhancement of relativistic electrons tends to occur during SBz-HSS events.
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Outer Radiation Belt boundary location relative to the magnetopause: Implications for magnetopause shadowing
Journal of Geophysical Research, 2011Co-Authors: C. Matsumura, Vassilis Angelopoulos, Yoshizumi Miyoshi, Kanako Seki, Shinya Saito, Josef KollerAbstract:[1] Relativistic electron fluxes of the Outer Radiation Belt often decrease rapidly in response to solar wind disturbances. The importance of the magnetopause shadowing (MPS) effect on such electron losses has yet to be quantified. If the MPS is essential for Outer Radiation Belt electron losses, a close relationship between the Outer edge of the Outer Belt and the magnetopause standoff distance is expected. Using GOES and THEMIS data, we examined earthward movement of the Outer edge of the Outer Belt during electron loss events at geosynchronous orbit and its correlation with the magnetopause standoff distance. In events with significant earthward movement, we found a good correlation. There were no clear correlations in events without significant earthward movement, however. Comparing the observational results with a test particle simulation, the observed dependence between the Outer edge and the magnetopause standoff distance is consistent with the MPS effect.
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a split in the Outer Radiation Belt by magnetopause shadowing test particle simulations
Journal of Geophysical Research, 2010Co-Authors: Shinya Saito, Yoshizumi Miyoshi, Kanako SekiAbstract:[1] We developed a three-dimensional relativistic test particle code and used it to calculate the trajectories of relativistic electrons in the Outer Radiation Belt. By applying time-varying magnetic field data calculated from the Tsyganenko model and using observed solar wind data and the Dst index, we examined the drift loss of relativistic electrons by magnetopause shadowing (MPS). Since other loss processes such as wave-particle interactions are not included in this simulation, the pure MPS effect can be discussed. A split was found in the Outer Radiation Belt after the enhancement of the solar wind dynamic pressure. Isolated electrons outside of the split have a narrow pitch angle distribution around 90° and are confined to a narrow range of the L shell. We found that the existence of the isolated electrons depends on the large geomagnetic tilt angle. These findings indicate that the split can be seen during summer and winter after MPS occurs. We suggest that this split in the Outer Radiation Belt during summer and winter is evidence that MPS actually causes the loss of the Outer Radiation Belt.
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Rebuilding process of the Outer Radiation Belt during the 3 November 1993 magnetic storm: NOAA and Exos‐D observations
Journal of Geophysical Research, 2003Co-Authors: Yoshizumi Miyoshi, Takahiro Obara, Akira Morioka, Hiroaki Misawa, T Nagai, Yoshiya KasaharaAbstract:[1] Using the data from the NOAA and Exos-D satellites during the 3 November 1993 magnetic storm, the dynamic behavior of electrons with energies from a few tens of kiloelectronvolts to a few and its relation to plasma waves were examined. After the late main phase, relativistic electron flux started to recover from the heart of the Outer Radiation Belt, where the cold plasma density was extremely low, and intense whistler mode chorus emissions were detected. The phase space density showed a peak in the Outer Belt, and the peak increased gradually. The simulation of the inward radial diffusion process could not reproduce the observed energy spectrum and phase space density variation. On the other hand, the simulated energy diffusion due to the gyroresonant electron-whistler mode wave interactions, under the assumption of the Kolmogorov turbulence spectrum, could generate the relativistic electrons without the flux transport from the Outer region. The present study suggested that the seed population of relativistic electrons, which appeared in the heart of the Outer Radiation Belt during the late main phase, was the ring current electrons injected from the plasma sheet, and that the acceleration by whistler mode chorus via gyroresonant wave–particle interactions outside the plasmapause could play an important role to generate the relativistic electrons.
