Bibliography
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Found 400 entries in the Bibliography.
Showing entries from 101 through 150
| 2019 |
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In this study, rapid loss of relativistic radiation belt electrons at low L* values (2.4\textendash3.2) during a strong geomagnetic storm on 22 June 2015 is investigated along with five possible loss mechanisms. Both the particle and wave data are obtained from the Van Allen Probes. Duskside H+ band electromagnetic ion cyclotron (EMIC) waves were observed during a rapid decrease of relativistic electrons with energy above 5.2 MeV occurring outside the plasmasphere during extreme magnetopause compression. Lower He+ composition and enriched O+ composition are found compared to typical values assumed in other studies of cyclotron resonant scattering of relativistic electrons by EMIC waves. Quantitative analysis demonstrates that even with the existence of He+ band EMIC waves, it is the H+ band EMIC waves that are likely to cause the depletion at small pitch angles and strong gradients in pitch angle distributions of relativistic electrons with energy above 5.2 MeV at low L values for this event. Very low frequency wave activity at other magnetic local time can be favorable for the loss of relativistic electrons at higher pitch angles. An illustrative calculation that combines the nominal pitch angle scattering rate due to whistler mode chorus at high pitch angles with the H+ band EMIC wave loss rate at low pitch angles produces loss on time scale observed at L=2.4\textendash3.2. At high L values and lower energies, radial loss to the magnetopause is a viable explanation. Qin, Murong; Hudson, Mary; Li, Zhao; Millan, Robyn; Shen, Xiaochen; Shprits, Yuri; Woodger, Leslie; Jaynes, Allison; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2018JA025726 cold ion composition; EMIC wave; minimum resonant energy; pitch angle diffusion; quasi-linear theory; relativistic electron loss; Van Allen Probes |
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Quenching of Equatorial Magnetosonic Waves by Substorm Proton Injections Near equatorial (fast) magnetosonic waves, characterized by high magnetic compressibility, are whistler-mode emissions destabilized by proton shell/ring distributions. In the past, substorm proton injections are widely known to intensify magnetosonic waves in the inner magnetosphere. Here we report the unexpected observations by the Van Allen Probes of the magnetosonic wave quenching associated with the substorm proton injections under both high- and low-density conditions. The enhanced proton thermal pressure distorted the background magnetic field configuration and the cold plasma density distribution. The reduced phase velocities locally allowed the weak growth or even damping of magnetosonic waves. Meanwhile, the spatially irregularly varying refractive indices might suppress the cumulative growth of magnetosonic waves. For intense injections, this wave quenching region could extend over 2 hr in magnetic local time and 0.5 Earth radii in radial distance. These results provide a new understanding of the generation and distribution of magnetosonic waves. Dai, Guyue; Su, Zhenpeng; Liu, Nigang; Wang, Bin; Zheng, Huinan; Wang, Yuming; Wang, Shui; Published by: Geophysical Research Letters Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2019GL082944 Bernstein mode instability; magnetosonic wave; Radiation belt; ring current; substorm injection; Van Allen Probes; Wave-particle interaction |
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Chorus waves are known to accelerate or scatter energetic electrons via quasi-linear or nonlinear wave-particle interactions in the Earth\textquoterights magnetosphere. In this letter, by taking advantage of simultaneous observations of chorus waveforms from at least a pair of probes among Van Allen Probes and/or Time History of Events and Macroscale Interactions during Substorms (THEMIS) missions, we statistically calculate the transverse size of lower band chorus wave elements. The average size of lower band chorus wave element is found to be ~315\textpm32 km over L shells of ~5\textendash6. Furthermore, our results suggest that the scale size of lower band chorus tends to be (1) larger at higher L shells; (2) larger at higher magnetic latitudes, especially on the dayside; and (3) larger in the azimuthal direction than in the radial direction. Our findings are crucial to quantify wave-particle interaction process, particularly the nonlinear interactions between chorus and energetic electrons. Shen, Xiao-Chen; Li, Wen; Ma, Qianli; Agapitov, Oleksiy; Nishimura, Yukitoshi; Published by: Geophysical Research Letters Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2019GL083118 |
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Triggered Plasmaspheric Hiss: Rising Tone Structures In this study, a rare hiss event observed by Van Allen Probe is reported and the possible generation is investigated based on wave and plasma measurements. The results suggest that the normal hiss (from 0.05fce to 0.5fce) with dominantly equatorward Poynting fluxes is locally generated by plasma sheet electrons via cyclotron instability. The low-frequency band (from 30 Hz to 0.05fce) with a mixture of equatorward and poleward Poynting fluxes is probably due to multiple reflections inside the plasmasphere. Such difference in the two bands is confirmed by the calculation of minimum energy of resonant electrons and local growth rate. Moreover, the analysis on the fine structures of normal hiss waves shows that besides the expected incoherent structure (below 1 kHz), several rising tone elements are measured above 1 kHz. The rising tone structures are probably triggered by the incoherent hiss part below 1 kHz, which is rarely reported before. Zhu, Hui; Liu, Xu; Chen, Lunjin; Published by: Geophysical Research Letters Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2019GL082688 Plasmaspheric Hiss; Radiation belts; Rising tone structure; Van Allen Probes |
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Electrostatic electron cyclotron harmonic (ECH) waves can yield diffuse aurora primarily at higher L-shells by driving efficient precipitation loss of plasma sheet electrons. Here using the Van Allen Probes high resolution data, we examine in detail the global occurrences of ECH waves during the period from October 1, 2012 to June 30, 2017 and find that there are totally 419 events of enhanced ECH waves. The statistical results demonstrate that ECH waves can be present over a broad region of L=4-6 and 00-24 MLT, with a higher occurrence in the region of L=5-6 and 06-19 MLT. The electron phase space density exhibits a distinct ring distribution (∂f/∂v⊥ >0) with the peak energy around a few keV. Both ECH wave events and the electron ring distributions are closely related and tend to be more distinct with increasing geomagnetic activity. Chen, Yaru; Zhou, Qinghua; He, Yihua; Yang, Chang; Liu, Si; Gao, Zhonglei; Xiao, Fuliang; Published by: Geophysical Research Letters Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2019GL082668 electron ring distribution; global occurrences; Radiation belt; Van Allen Probe observation; Van Allen Probes; waves |
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Electrostatic electron cyclotron harmonic (ECH) waves can yield diffuse aurora primarily at higher L-shells by driving efficient precipitation loss of plasma sheet electrons. Here using the Van Allen Probes high resolution data, we examine in detail the global occurrences of ECH waves during the period from October 1, 2012 to June 30, 2017 and find that there are totally 419 events of enhanced ECH waves. The statistical results demonstrate that ECH waves can be present over a broad region of L=4-6 and 00-24 MLT, with a higher occurrence in the region of L=5-6 and 06-19 MLT. The electron phase space density exhibits a distinct ring distribution (∂f/∂v⊥ >0) with the peak energy around a few keV. Both ECH wave events and the electron ring distributions are closely related and tend to be more distinct with increasing geomagnetic activity. Chen, Yaru; Zhou, Qinghua; He, Yihua; Yang, Chang; Liu, Si; Gao, Zhonglei; Xiao, Fuliang; Published by: Geophysical Research Letters Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2019GL082668 electron ring distribution; global occurrences; Radiation belt; Van Allen Probe observation; Van Allen Probes; waves |
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Investigation of Solar Proton Access into the inner magnetosphere on 11 September 2017 In this study, access of solar energetic protons to the inner magnetosphere on 11 September 2017 is investigated by computing the reverse particle trajectories with the Dartmouth geomagnetic cutoff code [Kress et al., 2010]. The maximum and minimum cutoff rigidity at each point along the orbit of Van Allen Probe A is numerically computed by extending the code to calculate cutoff rigidity for particles coming from arbitrary direction. Pulse-height analyzed (PHA) data has the advantage of providing individual particle energies and effectively excluding background high energy proton contamination. This technique is adopted to study the cutoff locations for solar protons with different energy. The results demonstrate that cutoff latitude is lower for solar protons with higher energy, consistent with low altitude vertical cutoffs. Both the observations and numerical results show that proton access into the inner magnetosphere depends strongly on angle between particle arrival direction and magnetic west. The numerical result is approximately consistent with the observation that the energy of almost all solar protons stays above the minimum cutoff rigidity. Qin, Murong; Hudson, Mary; Kress, Brian; Selesnick, Richard; Engel, Miles; Li, Zhao; Shen, Xiaochen; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2018JA026380 cutoff energy; cutoff location; Dartmouth geomagnetic cutoff code; Pulse height analyzed data; Solar proton; straggling function; Van Allen Probes |
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Modulation of Locally Generated Equatorial Noise by ULF Wave In this paper we report a rare and fortunate event of fast magnetosonic (MS, also called equatorial noise) waves modulated by compressional ultralow frequency (ULF) waves measured by Van Allen Probes. The characteristics of MS waves, ULF waves, proton distribution, and their potential correlations are analyzed. The results show that ULF waves can modulate the energetic ring proton distribution and in turn modulate the MS generation. Furthermore, the variation of MS intensities is attributed to not only ULF wave activities but also the variation of background parameters, for example, number density. The results confirm the opinion that MS waves are generated by proton ring distribution and propose a new modulation phenomenon. Zhu, Hui; Chen, Lunjin; Liu, Xu; Shprits, Yuri; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2018JA026199 linear growth rate; magnetosonic waves; Radiation belts; ULF waves; Van Allen Probes |
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We report on evidence for the generation of an ultra-low frequency plasma wave by the drift-mirror plasma instability in the dynamic plasma environment of Earth\textquoterights inner magnetosphere. The plasma measurements are obtained from the Radiation Belt Storm Probes Ion Composition Experiment onboard NASA\textquoterights Van Allen Probes Satellites. We show that the measured wave-particle interactions are driven by the drift-mirror instability. Theoretical analysis of the data demonstrates that the drift-mirror mode plasma instability condition is well satisfied. We also demonstrate, for the first time, that the measured wave growth rate agrees well with the predicted linear theory growth rate. Hence, the in-situ space plasma observations and theoretical analysis demonstrate that local generation of ultra-low frequency and high amplitude plasma waves can occur in the high beta plasma conditions of Earth\textquoterights inner magnetosphere. Soto-Chavez, A.; Lanzerotti, L.; Manweiler, J.; Gerrard, A.; Cohen, R.; Xia, Z.; Chen, L.; Kim, H.; Published by: Physics of Plasmas Published on: 04/2019 YEAR: 2019 DOI: 10.1063/1.5083629 |
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We report on evidence for the generation of an ultra-low frequency plasma wave by the drift-mirror plasma instability in the dynamic plasma environment of Earth\textquoterights inner magnetosphere. The plasma measurements are obtained from the Radiation Belt Storm Probes Ion Composition Experiment onboard NASA\textquoterights Van Allen Probes Satellites. We show that the measured wave-particle interactions are driven by the drift-mirror instability. Theoretical analysis of the data demonstrates that the drift-mirror mode plasma instability condition is well satisfied. We also demonstrate, for the first time, that the measured wave growth rate agrees well with the predicted linear theory growth rate. Hence, the in-situ space plasma observations and theoretical analysis demonstrate that local generation of ultra-low frequency and high amplitude plasma waves can occur in the high beta plasma conditions of Earth\textquoterights inner magnetosphere. Soto-Chavez, A.; Lanzerotti, L.; Manweiler, J.; Gerrard, A.; Cohen, R.; Xia, Z.; Chen, L.; Kim, H.; Published by: Physics of Plasmas Published on: 04/2019 YEAR: 2019 DOI: 10.1063/1.5083629 |
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Plasma kinetic theory predicts that sufficiently anisotropic proton distribution will excite electromagnetic ion cyclotron (EMIC) waves, which in turn relax the proton distribution to a marginally stable state creating an upper bound on the relaxed proton anisotropy. Here, using EMIC wave observations and coincident plasma measurements made by Van Allen Probes in the inner magnetosphere, we show that the proton distributions are well constrained by this instability to a marginally stable state. Near the threshold, the probability of EMIC wave occurrence is highest, having left-handed polarization and observed near the magnetic equator with relatively small wave normal angles, indicating that these waves are locally generated. In addition, EMIC waves are distributed in two magnetic local time regions with different intensity. Compared with helium band waves, hydrogen band waves behave similarly except that they are often observed in low-density regions. These results reveal several important features regarding EMIC waves excitation and propagation. Yue, Chao; Jun, Chae-Woo; Bortnik, Jacob; An, Xin; Ma, Qianli; Reeves, Geoffrey; Spence, Harlan; Gerrard, Andrew; Gkioulidou, Matina; Mitchell, Donald; Kletzing, Craig; Published by: Geophysical Research Letters Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2019GL082633 EMIC waves; helium-band; hydrogen-band; plasma beta; proton temperature anisotropy; Van Allen Probes |
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Ion transport from the plasma sheet to the ring current is the main cause of the development of the ring current. Energetic (>150 keV) ring current ions are known to be transported diffusively in several days. A recent study suggested that energetic oxygen ions are transported closer to the Earth than protons due to the diffusive transport caused by a combination of the drift and drift-bounce resonances with Pc 3\textendash5 ultralow frequency waves during the 24 April 2013 magnetic storm. To understand the occurrence conditions of such selective oxygen increase (SOI), we investigate the phase space densities (PSDs) between protons and oxygen ions with the first adiabatic invariants (μ) of 0.1\textendash2.0 keV/nT measured by the Radiation Belt Storm Probes Ion Composition Experiment instrument on the Van Allen Probes at L ~ 3\textendash6 during 90 magnetic storms in 2013\textendash2017. We identified the SOI events in which oxygen PSDs increase while proton PSDs do not increase during a period of ~9 hr (one orbital period). Among the 90 magnetic storms, 33\% were accompanied by the SOI events. Global enhancements of Pc 4 and Pc 5 waves observed by ground magnetometers during the SOI events suggest that radial transport due to combination of the drift-bounce resonance with Pc 4 oscillations and the drift resonance with Pc 5 oscillations can be the cause of SOIs. The contribution of the SOI events to the magnetic storm intensity is roughly estimated to be ~9\% on average. Mitani, K.; Seki, K.; Keika, K.; Gkioulidou, M.; Lanzerotti, L.; Mitchell, D.; Kletzing, C.; Yoshikawa, A.; Obana, Y.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2018JA026168 Magnetic Storms; Oxygen ions; ring current; Van Allen Probes |
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Electromagnetic ion cyclotron (EMIC) waves can drive precipitation of tens of keV protons and relativistic electrons, and are a potential candidate for causing radiation belt flux dropouts. In this study, we quantitatively analyze three cases of EMIC-driven precipitation, which occurred near the dusk sector observed by multiple Low-Earth-Orbiting (LEO) Polar Operational Environmental Satellites/Meteorological Operational satellite programme (POES/MetOp) satellites. During EMIC wave activity, the proton precipitation occurred from few tens of keV up to hundreds of keV, while the electron precipitation was mainly at relativistic energies. We compare observations of electron precipitation with calculations using quasi-linear theory. For all cases, we consider the effects of other magnetospheric waves observed simultaneously with EMIC waves, namely, plasmaspheric hiss and magnetosonic waves, and find that the electron precipitation at MeV energies was predominantly caused by EMIC-driven pitch angle scattering. Interestingly, each precipitation event observed by a LEO satellite extended over a limited L shell region (ΔL ~ 0.3 on average), suggesting that the pitch angle scattering caused by EMIC waves occurs only when favorable conditions are met, likely in a localized region. Furthermore, we take advantage of the LEO constellation to explore the occurrence of precipitation at different L shells and magnetic local time sectors, simultaneously with EMIC wave observations near the equator (detected by Van Allen Probes) or at the ground (measured by magnetometers). Our analysis shows that although EMIC waves drove precipitation only in a narrow ΔL, electron precipitation was triggered at various locations as identified by POES/MetOp over a rather broad region (up to ~4.4 hr MLT and ~1.4 L shells) with similar patterns between satellites. Capannolo, L.; Li, W.; Ma, Q.; Shen, X.-C.; Zhang, X.-J.; Redmon, R.; Rodriguez, J.; Engebretson, M.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Raita, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2018JA026291 EMIC waves; energetic electron precipitation; pitch angle scattering; quasi-linear theory; radiation belts dropouts; Van Allen Probes |
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Subauroral polarization streams (SAPS) prefer geomagnetically disturbed conditions and strongly correlate with geomagnetic indexes. However, the temporal evolution of SAPS and its relationship with dynamic and structured ring current and particle injection are still not well understood. In this study, we performed detailed analysis of temporal evolution of SAPS during a moderate storm on 18 May 2013 using conjugate observations of SAPS from the Van Allen Probes (VAP) and the Super Dual Auroral Radar Network (SuperDARN). The large-scale SAPS (LS-SAPS) formed during the main phase of this storm and decayed due to the northward turning of the interplanetary magnetic field. A mesoscale (approximately several hundreds of kilometers zonally) enhancement of SAPS was observed by SuperDARN at 0456 UT. In the conjugate magnetosphere, a large SAPS electric field (\~8 mV/m) pointing radially outward, a local magnetic field dip, and a dispersionless ion injection were observed simultaneously by VAP-A at L shell = 3.5 and MLT = 20. The particle injection observed by VAP-A is likely associated with the particle injection observed by the Geostationary Operational Environmental Satellite 15 near 20 MLT. Magnetic perturbations observed by the ground magnetometers and flow reversals observed by SuperDARN reveal that this mesoscale enhancement of SAPS developed near the Harang reversal and before the substorm onset. The observed complex signatures in both space and ground can be explained by a two-loop current wedge generated by the perturbed plasma pressure gradient and the diamagnetic effect of the structured ring current following particle injection. Wang, Zihan; Zou, Shasha; Shepherd, Simon; Liang, Jun; Gjerloev, Jesper; Ruohoniemi, Michael; Kunduri, Bharat; Wygant, John; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2019JA026535 Field-Aligned Current; Particle Injection; Sub-auroral Polarization Stream; Van Allen Probes |
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Whistler mode waves are important for precipitating energetic electrons into Earth\textquoterights upper atmosphere, while the quantitative effect of each type of whistler mode wave on electron precipitation is not well understood. In this letter, we evaluate energetic electron precipitation driven by three types of whistler mode waves: plume whistler mode waves, plasmaspheric hiss, and exohiss observed outside the plasmapause. By quantitatively analyzing three conjunction events between Van Allen Probes and POES/MetOp satellites, together with quasi-linear calculation, we found that plume whistler mode waves are most effective in pitch angle scattering loss, particularly for the electrons from tens to hundreds of keV. Our new finding provides the first direct evidence of effective pitch angle scattering driven by plume whistler mode waves and is critical for understanding energetic electron loss process in the inner magnetosphere. We suggest the effect of plume whistler mode waves be accurately incorporated into future radiation belt modeling. Li, W.; Shen, X.-C.; Ma, Q.; Capannolo, L.; Shi, R.; Redmon, R.; Rodriguez, J.; Reeves, G.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2019GL082095 electron precipitation; hiss; plasmaspheric plume; Plume wave; Van Allen Probes; whistler mode wave |
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Energy coupling between the solar wind and the Earth\textquoterights magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how Ultra Low Frequency (ULF) wave activity during the passage of Alfv\ enic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on September 22, 2014, which coincides with the corotating interaction region preceding a high-speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground and space-based observational data, global magnetohydrodynamic (MHD) simulations, and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L-shells. MHD simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfv\ en modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by Phase Space Density (PhSD) calculations for this global recovery period. Da Silva, L.; Sibeck, D.; Alves, L.; Souza, V.; Jauer, P.; Claudepierre, S.; Marchezi, J.; Agapitov, O.; Medeiros, C.; Vieira, L.; Wang, C.; Jiankui, S.; Liu, Z.; Gonzalez, W.; Dal Lago, A.; Rockenbach, M.; Padua, M.; Alves, M.; Barbosa, M.; Fok, M.-C.; Baker, D.; Kletzing, C.; Kanekal, S.; Georgiou, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA026184 alfv\ en fluctuations; Earth\textquoterights magnetosphere; high speed stream; Radiation belts; relativistic electron flux; ULF wave; Van Allen Probes |
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Initial Results From the GEM Challenge on the Spacecraft Surface Charging Environment Spacecraft surface charging during geomagnetically disturbed times is one of the most important causes of satellite anomalies. Predicting the surface charging environment is one prevalent task of the geospace environment models. Therefore, the Geospace Environment Modeling (GEM) Focus Group \textquotedblleftInner Magnetosphere Cross-energy/Population Interactions\textquotedblright initiated a community-wide challenge study to assess the capability of several inner magnetosphere ring current models in determining surface charging environment for the Van Allen Probes orbits during the 17 March 2013 storm event. The integrated electron flux between 10 and 50 keV is used as the metrics. Various skill scores are applied to quantitatively measure the modeling performance against observations. Results indicate that no model consistently perform the best in all of the skill scores or for both satellites. We find that from these simulations the ring current model with observational flux boundary condition and Weimer electric potential driver generally reproduces the most realistic flux level around the spacecraft. A simple and weaker Volland-Stern electric field is not capable of effectively transporting the same plasma at the boundary toward the Earth. On the other hand, if the ring current model solves the electric field self-consistently and obtains similar strength and pattern in the equatorial plane as the Weimer model, the boundary condition plays another crucial role in determining the electron flux level in the inner region. When the boundary flux spectra based on magnetohydrodynamics (MHD) model/empirical model deviate from the shape or magnitude of the observed distribution function, the simulation produces poor skill scores along Van Allen Probes orbits. Yu, Yiqun; ätter, Lutz; Jordanova, Vania; Zheng, Yihua; Engel, Miles; Fok, Mei-Ching; Kuznetsova, Maria; Published by: Space Weather Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018SW002031 GEM challenge; IMCEPI Focus Group; ring current model assessment; Space weather; spacecraft surface charging; Van Allen Probes |
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This work designs a new model called PreMevE to predict storm-time distributions of relativistic electrons within Earth\textquoterights outer radiation belt. This model takes advantage of the cross-energy, -L-shell, and \textendashpitch-angle coherence associated with wave-electron resonant interactions, ingests observations from belt boundaries\textemdashmainly by NOAA POES in low-Earth-orbits (LEOs), and provides high-fidelity nowcast (multiple-hour prediction) and forecast (> ~1 day) of MeV electron fluxes over L-shells between 2.8-7 through linear prediction filters. PreMevE can not only reliably anticipate incoming enhancements of MeV electrons during storms with at least 1-day forewarning time, but also accurately specify the evolving event-specific electron spatial distributions afterwards. The performance of PreMevE is assessed against long-term in situ data from one Van Allen Probe and a LANL geosynchronous satellite. This new model enhances our preparedness for severe MeV electron events in the future, and further adds new science utility to existing and next-generation LEO space infrastructure. Chen, Yue; Reeves, Geoffrey; Fu, Xiangrong; Henderson, Michael; Published by: Space Weather Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018SW002095 event-specific predictions; LANL GEO observations; linear predictive filters; MeV electron events; outer radiation belt; precipitation at low-earth-orbits (LEO); Van Allen Probes |
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This work designs a new model called PreMevE to predict storm-time distributions of relativistic electrons within Earth\textquoterights outer radiation belt. This model takes advantage of the cross-energy, -L-shell, and \textendashpitch-angle coherence associated with wave-electron resonant interactions, ingests observations from belt boundaries\textemdashmainly by NOAA POES in low-Earth-orbits (LEOs), and provides high-fidelity nowcast (multiple-hour prediction) and forecast (> ~1 day) of MeV electron fluxes over L-shells between 2.8-7 through linear prediction filters. PreMevE can not only reliably anticipate incoming enhancements of MeV electrons during storms with at least 1-day forewarning time, but also accurately specify the evolving event-specific electron spatial distributions afterwards. The performance of PreMevE is assessed against long-term in situ data from one Van Allen Probe and a LANL geosynchronous satellite. This new model enhances our preparedness for severe MeV electron events in the future, and further adds new science utility to existing and next-generation LEO space infrastructure. Chen, Yue; Reeves, Geoffrey; Fu, Xiangrong; Henderson, Michael; Published by: Space Weather Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018SW002095 event-specific predictions; LANL GEO observations; linear predictive filters; MeV electron events; outer radiation belt; precipitation at low-earth-orbits (LEO); Van Allen Probes |
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Simulations of Electron Energization and Injection by BBFs Using High-Resolution LFM MHD Fields We study electron injection and energization by bursty bulk flows (BBFs), by tracing electron trajectories using magnetohydrodynamic (MHD) field output from the Lyon-Fedder-Mobarry (LFM) code. The LFM MHD simulations were performed using idealized solar wind conditions to produce BBFs. We show that BBFs can inject energetic electrons of few to 100 keV from the magnetotatail beyond -24 RE to inward of geosynchronous, while accelerating them in the process. We also show the dependence of energization and injection on the initial relative position of the electrons to the magnetic field structure of the BBF, the initial pitch angle, and the initial energy. In addition, we have shown that the process can be nonadiabatic with violation of the first adiabatic invariant (μ). Further, we discuss the mechanism of energization and injection in order to give generalized insight into the process. Eshetu, W.; Lyon, J.; Hudson, M.; Wiltberger, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA025789 |
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Using observations from the Van Allen Probes EMFISIS instrument, coupled with ray tracing simulations, we determine the fraction of chorus wave power with the conditions required to access the plasmasphere and evolve into plasmaspheric hiss. It is found that only an extremely small fraction of chorus occurs with the required wave vector orientation, carrying only a small fraction of the total chorus wave power. The exception is on the edge of plasmaspheric plumes, where strong azimuthal density gradients are present. In these cases, up to 94\% of chorus wave power exists with the conditions required to access the plasmasphere. As such, we conclude that strong azimuthal density gradients are actually a requirement if a significant fraction of chorus wave power is to enter the plasmasphere and be a source of plasmaspheric hiss. This result suggests it is unlikely that chorus directly contributes a significant fraction of plasmaspheric hiss wave power. Hartley, D.; Kletzing, C.; Chen, L.; Horne, R.; ik, O.; Published by: Geophysical Research Letters Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2019GL082111 chorus waves; EMFISIS; Plasmaspheric Hiss; plasmaspheric plumes; Van Allen Probes; wave normal angle |
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Global Empirical Picture of Magnetospheric Substorms Inferred From Multimission Magnetometer Data Magnetospheric substorms represent key explosive processes in the interaction of the Earth\textquoterights magnetosphere with the solar wind, and their understanding and modeling are critical for space weather forecasting. During substorms, the magnetic field on the nightside is first stretched in the antisunward direction and then it rapidly contracts earthward bringing hot plasmas from the distant space regions into the inner magnetosphere, where they contribute to geomagnetic storms and Joule dissipation in the polar ionosphere, causing impressive splashes of aurora. Here we show for the first time that mining millions of spaceborne magnetometer data records from multiple missions allows one to reconstruct the global 3-D picture of these stretching and dipolarization processes. Stretching results in the formation of a thin (less than the Earth\textquoterights radius) and strong current sheet, which is diverted into the ionosphere during dipolarization. In the meantime, the dipolarization signal propagates further into the inner magnetosphere resulting in the accumulation of a longer lived current there, giving rise to a protogeomagnetic storm. The global 3-D structure of the corresponding substorm currents including the substorm current wedge is reconstructed from data. Stephens, G.; Sitnov, M.; Korth, H.; Tsyganenko, N.; Ohtani, S.; Gkioulidou, M.; Ukhorskiy, A; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA025843 Current sheet thinning; Data-mining; Magnetotail dipolarization; Storm-substorm relationship; substorm current wedge; substorms; Van Allen Probes |
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Local Generation of High-Frequency Plasmaspheric Hiss Observed by Van Allen Probes The generation of a high-frequency plasmaspheric hiss (HFPH) wave observed by Van Allen Probes is studied in this letter for the first time. The wave has a moderate power spectral density (\~10-6 nT2/Hz), with a frequency range extended from 2 to 10 kHz. The correlated observations of waves and particles indicate that HFPH is associated with the enhancement of electron flux during the substorm on 6 January 2014. Calculations of the wave linear growth rate driven by the fitted electron phase space density show that the electron distribution after the substorm onset is efficient for the HFPH generation. The energy of the contributing electrons is about 1\textendash2 keV, which is consistent with the observation. These results support that the observed HFPH is likely to be generated locally inside the plasmasphere due to the instability of injected kiloelectron volt electrons. He, Zhaoguo; Chen, Lunjin; Liu, Xu; Zhu, Hui; Liu, Si; Gao, Zhonglei; Cao, Yong; Published by: Geophysical Research Letters Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018GL081578 electron; high frequency; local generation; Plasmaspheric Hiss; substorm injection; Van Allen Probes |
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Local Generation of High-Frequency Plasmaspheric Hiss Observed by Van Allen Probes The generation of a high-frequency plasmaspheric hiss (HFPH) wave observed by Van Allen Probes is studied in this letter for the first time. The wave has a moderate power spectral density (\~10-6 nT2/Hz), with a frequency range extended from 2 to 10 kHz. The correlated observations of waves and particles indicate that HFPH is associated with the enhancement of electron flux during the substorm on 6 January 2014. Calculations of the wave linear growth rate driven by the fitted electron phase space density show that the electron distribution after the substorm onset is efficient for the HFPH generation. The energy of the contributing electrons is about 1\textendash2 keV, which is consistent with the observation. These results support that the observed HFPH is likely to be generated locally inside the plasmasphere due to the instability of injected kiloelectron volt electrons. He, Zhaoguo; Chen, Lunjin; Liu, Xu; Zhu, Hui; Liu, Si; Gao, Zhonglei; Cao, Yong; Published by: Geophysical Research Letters Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018GL081578 electron; high frequency; local generation; Plasmaspheric Hiss; substorm injection; Van Allen Probes |
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Low-Energy ( The heavy ion component of the low-energy (eV to hundreds of eV) ion population in the inner magnetosphere, also known as the O+ torus, is a crucial population for various aspects of magnetospheric dynamics. Yet even though its existence has been known since the 1980s, its formation remains an open question. We present a comprehensive study of a low-energy ( Gkioulidou, Matina; Ohtani, S.; Ukhorskiy, A; Mitchell, D.; Takahashi, K.; Spence, H.; Wygant, J.; Kletzing, C.; Barnes, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA025862 |
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We present the temporal evolution of electron Phase Space Density (PSD) in the outer radiation belt during the intense March 2015 geomagnetic storm. Comparing observed PSD profiles as a function of L* at fixed first, M, and second, K, adiabatic invariants with those produced by simulations is critical for determining the physical processes responsible for the outer radiation belt dynamics. Here we show that the bulk of the accelerated and enhanced outer radiation belt population consists of electrons with K < 0.17 G1/2Re. For these electrons, the observed PSD versus L* profiles during the recovery phase of the storm have a positive radial gradient. We compare the observed temporal evolution of the PSD profiles during the recovery phase with those produced by radial diffusion simulations driven by observed Ultralow Frequency wave power as measured on the ground. Our results indicate that the dominant flux enhancement, inside L* < 5, in the heart of the outer radiation belt during the March 2015 geomagnetic storm is consistent with that produced by fast inward radial diffusion of electrons from a dynamic outer boundary driven by enhanced Ultralow Frequency wave power. Ozeke, L.; Mann, I.; Claudepierre, S.; Henderson, M.; Morley, S.; Murphy, K.; Olifer, L.; Spence, H.; Baker, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA026326 Local Acceleration; March 2015 storm; Phase space density; radial diffusion; Radiation belt; ULF waves; Van Allen Probes |
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Storm Time EMIC Waves Observed by Swarm and Van Allen Probe Satellites The temporal and spatial evolution of electromagnetic ion cyclotron (EMIC) waves during the magnetic storm of 21\textendash29 June 2015 was investigated using high-resolution magnetic field observations from Swarm constellation in the ionosphere and Van Allen Probes in the magnetosphere. Magnetospheric EMIC waves had a maximum occurrence frequency in the afternoon sector and shifted equatorward during the expansion phase and poleward during the recovery phase. However, ionospheric waves in subauroral regions occurred more frequently in the nighttime than during the day and exhibited less obvious latitudinal movements. During the main phase, dayside EMIC waves occurred in both the ionosphere and magnetosphere in response to the dramatic increase in the solar wind dynamic pressure. Waves were absent in the magnetosphere and ionosphere around the minimum SYM-H. During the early recovery phase, He+ band EMIC waves were observed in the ionosphere and magnetosphere. During the late recovery phase, H+ band EMIC waves emerged in response to enhanced earthward convection during substorms in the premidnight sector. The occurrence of EMIC waves in the noon sector was affected by the intensity of substorm activity. Both ionospheric wave frequency and power were higher in the summer hemisphere than in the winter hemisphere. Waves were confined to an MLT interval of less than 5 hr with a duration of less than 186 min from coordinated observations. The results could provide additional insights into the spatial characteristics and propagation features of EMIC waves during storm periods. Wang, Hui; He, Yangfan; ühr, Hermann; Kistler, Lynn; Saikin, Anthony; Lund, Eric; Ma, Shuying; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA026299 |
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The evolution of the radiation belts in L-shell (L), energy (E), and equatorial pitch-angle (α0) is analyzed during the calm 11-day interval (March 4 \textendashMarch 15) following the March 1 storm 2013. Magnetic Electron and Ion Spectrometer (MagEIS) observations from Van Allen Probes are interpreted alongside 1D and 3D Fokker-Planck simulations combined with consistent event-driven scattering modeling from whistler mode hiss waves. Three (L, E, α0)-regions persist through 11 days of hiss wave scattering; the pitch-angle dependent inner belt core (L~<2.2 and E<700 keV), pitch-angle homogeneous outer belt low-energy core (L>~5 and E~<100 keV), and a distinct pocket of electrons (L~[4.5, 5.5] and E~[0.7, 2] MeV). The pitch-angle homogeneous outer belt is explained by the diffusion coefficients that are roughly constant for α0~<60\textdegree, E>100 keV, 3.5 Ripoll, -F.; Loridan, V.; Denton, M.; Cunningham, G.; Reeves, G.; ik, O.; Fennell, J.; Turner, D.; Drozdov, A; Villa, J.; Shprits, Y; Thaller, S.; Kurth, W.; Kletzing, C.; Henderson, M.; Ukhorskiy, A; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2018 YEAR: 2018 DOI: 10.1029/2018JA026111 electron lifetime; hiss waves; pitch-angle diffusion coefficient; Radiation belts; Van Allen Probes; wave particle interactions |
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Electromagnetic whistler-mode chorus and electrostatic electron cyclotron harmonic (ECH) waves can contribute significantly to auroral electron precipitation and radiation belt electron acceleration. In the past, linear and nonlinear wave-particle interactions have been proposed to explain the occurrences of these magnetospheric waves. By analyzing Van Allen Probes data, we present here the first evidence for nonlinear coupling between chorus and ECH waves. The sum-frequency and difference-frequency interactions produced the ECH sidebands with discrete frequency sweeping structures exactly corresponding to the chorus rising tones. The newly-generated weak sidebands did not satisfy the original electrostatic wave dispersion relation. After the generation of chorus and normal ECH waves by hot electron instabilities, the nonlinear wave-wave interactions could additionally redistribute energy among the resonant waves, potentially affecting to some extent the magnetospheric electron dynamics. Gao, Zhonglei; Su, Zhenpeng; Xiao, Fuliang; Summers, Danny; Liu, Nigang; Zheng, Huinan; Wang, Yuming; Wei, Fengsi; Wang, Shui; Published by: Geophysical Research Letters Published on: 11/2018 YEAR: 2018 DOI: 10.1029/2018GL080635 aurora; Chorus wave; electron cyclotron harmonic wave; nonlinear wave-wave interaction; Radiation belt; Van Allen Probes |
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There has been increasing evidence for pitch angle scattering of relativistic electrons by electromagnetic ion cyclotron (EMIC) waves. Theoretical studies have predicted that the loss time scale of MeV electrons by EMIC waves can be very fast, suggesting that MeV electron fluxes rapidly decrease in association with the EMIC wave activity. This study reports on a unique event of MeV electron loss induced by EMIC waves based on Arase, Van Allen Probes, and ground-based network observations. Arase observed a signature of MeV electron loss by EMIC waves, and the satellite and ground-based observations constrained spatial-temporal variations of the EMIC wave activity during the loss event. Multi-satellite observation of MeV electron fluxes showed that ~2.5 MeV electron fluxes substantially decreased within a few tens of minutes where the EMIC waves were present. The present study provides an observational estimate of the loss time scale of MeV electrons by EMIC waves. Kurita, S.; Miyoshi, Y.; Shiokawa, K.; Higashio, N.; Mitani, T.; Takashima, T.; Matsuoka, A.; Shinohara, I.; Kletzing, C.; Blake, J.; Claudepierre, S.; Connors, M.; Oyama, S.; Nagatsuma, T.; Sakaguchi, K.; Baishev, D.; Otsuka, Y.; Published by: Geophysical Research Letters Published on: 11/2018 YEAR: 2018 DOI: 10.1029/2018GL080262 EMIC waves; loss; PWING project; Radiation belt; The Arase satellite; Van Allen Probes |
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Whistler mode exohiss are the structureless hiss waves observed outside the plasmapause with featured equatorward Poynting flux. An event of the amplification of exohiss as well as chorus waves was recorded by Van Allen Probes during the recovery phase of a weak geomagnetic storm. Amplitudes of both types of the waves showed a significant increase at the regions of electron density enhancements. It is found that the electrons resonant with exohiss and chorus showed moderate pitch-angle anisotropies. The ratio of the number of electrons resonating with exohiss to total electron number presented in-phase correlation with density variations, which suggests that exohiss can be amplified due to electron density enhancement in terms of cyclotron instability. The calculation of linear growth rates further supports above conclusion. We suggest that exohiss waves have potential to become more significant due to the background plasma fluctuation. Zhu, Hui; Shprits, Yuri; Chen, Lunjin; Liu, Xu; Kellerman, Adam; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2018 YEAR: 2018 DOI: 10.1029/2017JA025023 electromagnetic waves; Exohiss; linear theory; Radiation belts; Van Allen Probes |
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Pitch Angle Scattering of Energetic Electrons by BBFs Field line curvature scattering by the magnetic field structure associated with bursty bulk flows (BBFs) has been studied, using simulated output fields from the Lyon-Fedder-Mobarry global magnetohydrodynamic code for specified solar wind input. There are weak magnetic field strength (B) regions adjacent to BBFs observed in the simulations. We show that these regions can cause strong scattering where the first adiabatic invariant changes by several factors within one equatorial crossing of energetic electrons of a few kiloelectron volts when the BBFs are beyond 10RE geocentric in the tail. Scattering by BBFs decreases as they move toward the Earth or when the electron energy decreases. For radiation belt electrons near or inside geosynchronous orbit we demonstrate that the fields associated with BBFs can cause weak scattering where the fractional change of the first invariant (μ0) within one equatorial crossing is small, but the change due to several crossings can accumulate. For the weak scattering case we developed a method of calculating the pitch angle diffusion coefficient Dαα. Dαα for radiation belt electrons for one particular BBF were calculated as a function of initial energy, equatorial pitch angle, and radial location. These Dαα values were compared to calculated Dαα for a dipole field with no electric field. We further compared Dαα values with that of stretched magnetic fields calculated by Artemyev et al. (2013, https://doi.org/10.5194/angeo-31-1485-2013) at r≈7RE. Results show that scattering by BBFs can be comparable to the most highly stretched magnetic field they studied. Eshetu, W.; Lyon, J.; Hudson, M.; Wiltberger, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2018 YEAR: 2018 DOI: 10.1029/2018JA025788 |
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We report a typical event that fast magnetosonic (MS) waves, exohiss, and two-band chorus waves occurred simultaneously on the dayside observed by Van Allen Probes on 25 December 2013. By combining calculations of electron diffusion coefficients and 2-D Fokker-Planck diffusion simulations, we quantitatively analyze the combined scattering effect of multiple waves to demonstrate that the net impact of combined scattering does not simply depend on the wave intensity dominance of various plasma waves. Although the observed MS waves are most intense, the electron butterfly distribution is inhibited by exohiss and chorus, and electrons are considerably accelerated by combined scattering of MS and chorus waves. The simulated electron pitch angle distributions exhibit the variation trend consistent with the observations. Our results strongly suggest that competition and cooperation between resonant interactions with concurrently occurring magnetospheric waves need to be carefully treated in modeling and comprehending the radiation belt electron dynamics. Hua, Man; Ni, Binbin; Fu, Song; Gu, Xudong; Xiang, Zheng; Cao, Xing; Zhang, Wenxun; He, Ying; Huang, He; Lou, Yuequn; Zhang, Yang; Published by: Geophysical Research Letters Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018GL079533 Combined scattering effect; diffusion simulations; Exohiss; magnetosonic waves; resonant wave-particle interactions; two-band chorus waves; Van Allen Probes |
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Inward radial diffusion driven by ULF waves has long been known to be capable of accelerating radiation belt electrons to very high energies within the heart of the belts, but more recent work has shown that radial diffusion values can be highly event-specific and mean values or empirical models may not capture the full significance of radial diffusion to acceleration events. Here we present an event of fast inward radial diffusion, occurring during a period following the geomagnetic storm of 17 March 2015. Ultra-relativistic electrons up to \~8 MeV are accelerated in the absence of intense higher-frequency plasma waves, indicating an acceleration event in the core of the outer belt driven primarily or entirely by ULF wave-driven diffusion. We examine this fast diffusion rate along with derived radial diffusion coefficients using particle and fields instruments on the Van Allen Probes spacecraft mission. Jaynes, A.; Ali, A.; Elkington, S.; Malaspina, D.; Baker, D.; Li, X.; Kanekal, S.; Henderson, M.; Kletzing, C.; Wygant, J.; Published by: Geophysical Research Letters Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018GL079786 Magnetosphere; radial diffusion; Radiation belts; ULF waves; Van Allen Probes |
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Generation of lower L -shell dayside chorus by energetic electrons from the plasmasheet Currently, the generation mechanism for the lower L-shell dayside chorus has still remained an open question. Here, we report two storm events: 06-07 March 2016 and 20-21 January 2016, when Van Allen Probes observed enhanced dayside chorus with lower and higher wave normal angles (the angles between the wave vector and the geomagnetic field) in the region of L = 3.5-6.3 and MLT = 5.6-13.5. Hot and energetic (\~ 1-100 keV) electrons displayed enhancements in fluxes and anisotropy when they were injected from the plasmasheet and drifted from midnight through dawn toward the dayside. Calculations of chorus local growth rates under different waves normal angles show that the upper cutoff and peak wave frequencies display similar patterns to the observations. Chorus growth rates maximize for the parallel propagation and drop with increasing wave normal angles. The current results confirm that the observed lower L-shell dayside chorus can be excited by anisotropic electrons originating from the plasmasheet in drifting from the nightside to the dayside. He, Yihua; Xiao, Fuliang; Su, Zhenpeng; Zheng, Huinan; Yang, Chang; Liu, Si; Zhou, Qinghua; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2017JA024889 Dayside chorus generation; Radiation belt; Van Allen Probes; Wave-particle interaction |
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Generation of lower L -shell dayside chorus by energetic electrons from the plasmasheet Currently, the generation mechanism for the lower L-shell dayside chorus has still remained an open question. Here, we report two storm events: 06-07 March 2016 and 20-21 January 2016, when Van Allen Probes observed enhanced dayside chorus with lower and higher wave normal angles (the angles between the wave vector and the geomagnetic field) in the region of L = 3.5-6.3 and MLT = 5.6-13.5. Hot and energetic (\~ 1-100 keV) electrons displayed enhancements in fluxes and anisotropy when they were injected from the plasmasheet and drifted from midnight through dawn toward the dayside. Calculations of chorus local growth rates under different waves normal angles show that the upper cutoff and peak wave frequencies display similar patterns to the observations. Chorus growth rates maximize for the parallel propagation and drop with increasing wave normal angles. The current results confirm that the observed lower L-shell dayside chorus can be excited by anisotropic electrons originating from the plasmasheet in drifting from the nightside to the dayside. He, Yihua; Xiao, Fuliang; Su, Zhenpeng; Zheng, Huinan; Yang, Chang; Liu, Si; Zhou, Qinghua; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2017JA024889 Dayside chorus generation; Radiation belt; Van Allen Probes; Wave-particle interaction |
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The Response of the Energy Content of the Outer Electron Radiation Belt to Geomagnetic Storms Using the data from the Van Allen Probe-A spacecraft, the variability of the total outer radiation belt (2.5 Xiong, Ying; Xie, Lun; Chen, Lunjin; Ni, Binbin; Fu, Suiyan; Pu, Zuyin; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018JA025475 Chorus wave; energetic particles; energy content; magnetic storm; outer radiation belt; Van Allen Probes |
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In one model, Pi2 pulsations are driven pulse by pulse by fast mode pulses that are launched as periodic bursty bulk flows brake when they approach the Earth. We have examined this model by analyzing data from multiple spacecraft and ground magnetometers for a Pi2 pulsation event. During the event, which started at \~2226 UT on 8 November 2014, Time History of Events and Macroscale Interactions during Substorms (THEMIS)-D detected an \~2 min period plasma bulk flow oscillation in the near-Earth magnetotail, while THEMIS-E and Van Allen Probes-B, both located on the nightside just earthward of the electron plasmapause, detected a Pi2 pulsation consisting of a 10 mHz oscillation in the azimuthal component of the electric field and a 19-mHz oscillation in the compressional component of the magnetic field. On the ground, magnetic field oscillations containing both frequencies were observed both on the nightside and on the dayside. The nightside observations indicated that the pulsation had a radially standing structure, which is consistent with plasmaspheric virtual resonances (PVRs) excited in a magnetohydrodynamic simulation assuming an impulsive energy source. Cross-spectral analysis of the magnetotail flow oscillation and the Pi2 pulsation indicated low coherence between them. These results suggest that the flow oscillation contributed to the Pi2 pulsation as a broadband energy source and that only the spectral components matching the PVR frequencies were detected with well-defined frequencies. Ionospheric currents connected to the PVRs may be responsible for the appearance of the pulsation on the dayside. Takahashi, Kazue; Hartinger, Michael; Vellante, Massimo; Heilig, azs; Lysak, Robert; Lee, Dong-Hun; Smith, Charles; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018JA025664 |
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A Statistical Survey of Radiation Belt Dropouts Observed by Van Allen Probes A statistical analysis on the radiation belt dropouts is performed based on 4 years of electron phase space density data from the Van Allen Probes. The μ, K, and L* dependence of dropouts and their driving mechanisms and geomagnetic and solar wind conditions are investigated using electron phase space density data sets for the first time. Our results suggest that electronmagnetic ion cyclotron (EMIC) wave scattering is the dominant dropout mechanism at low L* region, which requires the most active geomagnetic and solar wind conditions. In contrast, dropouts at high L* have a higher occurrence and are due to a combination of EMIC wave scattering and outward radial diffusion associated with magnetopause shadowing. In addition, outward radial diffusion at high L* is found to cause larger dropouts than EMIC wave scattering and is accompanied with active geomagnetic and solar wind drivers. Xiang, Zheng; Tu, Weichao; Ni, Binbin; Henderson, M.; Cao, Xing; Published by: Geophysical Research Letters Published on: 08/2018 YEAR: 2018 DOI: 10.1029/2018GL078907 EMIC wave; magnetopause shadowing; Phase space density; radial diffusion; radiation belt dropout; Van Allen Probes; wave particle interaction |
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The composition of plasma inside geostationary orbit based on Van Allen Probes observations The composition of the inner magnetosphere is of great importance for determining the plasma pressure, and thus the currents and magnetic field configuration. In this study, we perform a statistical survey of equatorial plasma pressure distributions and investigate the relative contributions of ions and electron with different energies inside of geostationary orbit under two AE levels based on over sixty months of observations from the HOPE and RBSPICE mass spectrometers on board Van Allen Probes. We find that the total and partial pressures of different species increase significantly at high AE levels with Hydrogen (H+) pressure being dominant in the plasmasphere. The pressures of the heavy ions and electrons increase outside the plasmapause and develop a strong dawn-dusk asymmetry with ion pressures peaking at dusk and electron pressure peaking at dawn. In addition, ring current H+ with energies ranging from 50 keV up to several hundred keV is the dominant component of plasma pressure during both quiet (> 90\%) and active times (> 60\%), while Oxygen (O+) with 10 < E < 50 keV and electrons with 0.1 < E < 40 keV become important during active times contributing more than 25\% and 20\% on the nightside, respectively, while the Helium (He+) contribution is generally small. The results presented in this study provide a global picture of the equatorial plasma pressure distributions and the associated contributions from different species with different energy ranges, which advance our knowledge of wave generation and provide models with a systematic baseline of plasma composition. Yue, Chao; Bortnik, Jacob; Li, Wen; Ma, Qianli; Gkioulidou, Matina; Reeves, Geoffrey; Wang, Chih-Ping; Thorne, Richard; T. Y. Lui, Anthony; Gerrard, Andrew; Spence, Harlan; Mitchell, Donald; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018JA025344 ion composition; plasma pressure; Plasmapause; Van Allen Probes |
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Evidence of Microbursts Observed Near the Equatorial Plane in the Outer Van Allen Radiation Belt We present the first evidence of electron microbursts observed near the equatorial plane in Earth\textquoterights outer radiation belt. We observed the microbursts on March 31st, 2017 with the Magnetic Electron Ion Spectrometer and RBSP Ion Composition Experiment on the Van Allen Probes. Microburst electrons with kinetic energies of 29-92 keV were scattered over a substantial range of pitch angles, and over time intervals of 150-500 ms. Furthermore, the microbursts arrived without dispersion in energy, indicating that they were recently scattered near the spacecraft. We have applied the relativistic theory of wave-particle resonant diffusion to the calculated phase space density, revealing that the observed transport of microburst electrons is not consistent with the hypothesized quasi-linear approximation. Shumko, Mykhaylo; Turner, Drew; O\textquoterightBrien, T.; Claudepierre, Seth; Sample, John; Hartley, D.; Fennell, Joseph; Blake, Bernard; Gkioulidou, Matina; Mitchell, Donald; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL078451 |
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Magnetosonic waves play a potentially important role in the complex evolution of the radiation belt electrons. These waves typically appear as discrete emission lines along the proton gyrofrequency harmonics, consistent with the prediction of the local Bernstein mode instability of hot proton ring distributions. Magnetosonic waves are nearly dispersionless particularly at low harmonics and therefore have the roughly unchanged frequency-time structures during the propagation. On the basis of Van Allen Probes observations, we here present the first report of magnetosonic harmonic falling and rising frequency emissions. They lasted for up to 2 h and occurred primarily in the dayside plasmatrough following intense substorms. These harmonic emission lines were well spaced by the proton gyrofrequency but exhibited a clear falling (rising) frequency characteristic in a regime with the temporal increase (decrease) of the proton gyrofrequency harmonics. Such unexpected structures might be produced by the nonlinear interactions between the locally generated magnetosonic waves at the proton gyrofrequency harmonics and a constant frequency magnetosonic wave propagating away from the Earth. Liu, Nigang; Su, Zhenpeng; Zheng, Huinan; Wang, Yuming; Wang, Shui; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL079232 Bernstein mode instability; magnetosonic wave; Radiation belt; ring current; rising/falling frequency; Van Allen Probes; wave propagation |
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Much of plasma heating and transport from the magnetotail into the inner magnetosphere occurs in the form of mesoscale discrete injections associated with sharp dipolarizations of magnetic field (dipolarization fronts). In this paper we investigate the role of magnetic trapping in acceleration and transport of the plasmasheet ions into the ring current. For this purpose we use high-resolution global MHD and three-dimensional test-particle simulations. It is shown that trapping, produced by sharp magnetic field gradients at the interface between dipolarizations and the ambient plasma, affect plasmasheet protons with energies above approximately 10 keV, enabling their transport across more than 10 Earth radii and acceleration by a factor of 10. Our estimates show that trapping is important to the buildup of the ring current plasma pressure of injected particles; depending on the plasmasheet temperature and energy spectrum, trapped protons can contribute between 20\% to 60\% of the plasma pressure. It is also shown that the acceleration process does not conserve the particle first invariant; on average protons are accelerated to higher energies compared to a purely adiabatic process. We also investigate how trapping and energization varies for deferent ions species and show that, in accordance with recent observations, ion acceleration is proportional to the ion charge and is independent of its mass. Ukhorskiy, A; Sorathia, K.; Merkin, V.; Sitnov, M.; Mitchell, D.; Gkioulidou, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025370 injections; plasma pressure; ring current; trapping; Van Allen Probes |
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Observed propagation route of VLF transmitter signals in the magnetosphere Signals of powerful ground transmitters at various places have been detected by satellites in near-Earth space. The study on propagation mode, ducted or nonducted, has attracted much attentions for several decades. Based on the statistical results from Van Allen Probes (data from Oct. 2012 to Mar. 2017) and DEMETER satellite (from Jan. 2006 to Dec. 2007), we present the ground transmitter signals distributed clearly in ionosphere and magnetosphere. The observed propagation route in the meridian plane in the magnetosphere for each of various transmitters from the combination of DEMETER and Van Allen Probes data in night time is revealed for the first time. We use realistic ray tracing simulation and compare simulation results against Van Allen Probes and DEMETER observation. By comparison we demonstrate that the observed propagation route, with partial deviation from the field lines corresponding to ground stations, provides direct and clear statistical evidence that the nonducted propagation mode plays a main role, although with partial contribution from ducted propagation. The propagation characteristics of VLF transmitter signals in the magnetosphere are critical for quantitatively assessing their contribution to energetic electron loss in radiation belts. Zhang, Zhenxia; Chen, Lunjin; Li, Xinqiao; Xia, Zhiyang; Heelis, Roderick; Horne, Richard; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025637 ducted propagation; in magnetosphere; nonducted propagation; Van Allen Probes; VLF transmitter |
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Observed propagation route of VLF transmitter signals in the magnetosphere Signals of powerful ground transmitters at various places have been detected by satellites in near-Earth space. The study on propagation mode, ducted or nonducted, has attracted much attentions for several decades. Based on the statistical results from Van Allen Probes (data from Oct. 2012 to Mar. 2017) and DEMETER satellite (from Jan. 2006 to Dec. 2007), we present the ground transmitter signals distributed clearly in ionosphere and magnetosphere. The observed propagation route in the meridian plane in the magnetosphere for each of various transmitters from the combination of DEMETER and Van Allen Probes data in night time is revealed for the first time. We use realistic ray tracing simulation and compare simulation results against Van Allen Probes and DEMETER observation. By comparison we demonstrate that the observed propagation route, with partial deviation from the field lines corresponding to ground stations, provides direct and clear statistical evidence that the nonducted propagation mode plays a main role, although with partial contribution from ducted propagation. The propagation characteristics of VLF transmitter signals in the magnetosphere are critical for quantitatively assessing their contribution to energetic electron loss in radiation belts. Zhang, Zhenxia; Chen, Lunjin; Li, Xinqiao; Xia, Zhiyang; Heelis, Roderick; Horne, Richard; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025637 ducted propagation; in magnetosphere; nonducted propagation; Van Allen Probes; VLF transmitter |
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Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit This paper examines how hydrogen, helium and oxygen (H, He and O) ion fluxes at 1\textendash1000 keV typically respond to local magnetic dipolarization inside geosynchronous orbit (GEO). We extracted 144 dipolarizations which occurred at magnetic inclination > 30\textdegree from the 2012\textendash2016 tail seasons\textquoteright observations of the Van Allen Probes spacecraft and then defined typical flux changes of these ion species by performing a superposed epoch analysis. On average, the dipolarization inside GEO is accompanied by a precursory transient decrease in the northward magnetic field component, transient impulsive enhancement in the westward electric field component, and decrease (increase) in the proton density (temperature). The coincident ion species experience an energy-dependent flux change, consisting of enhancement (depression) at energies above (below) ~50 keV. These properties morphologically resemble those around dipolarization fronts (or fast flows) in the near-Earth tail. A distinction among the ion species is the average energy of the flux ratio peak, being at 200\textendash400 keV (100\textendash200 keV) for He (H and O) ions. The flux ratio peaks at different energies likely reflect the different charge states of injected ionospheric- and/or solar wind-origin ion species. The ion spectra become harder for sharp dipolarizations, suggesting the importance of accompanying electric field in transporting and/or energizing the ions efficiently. Interestingly, the average flux ratio peak does not differ significantly among the ion species for ~2 min after onset, which implies that mass-dependent acceleration process is less important in the initial stage of dipolarization. Motoba, T.; Ohtani, S.; Gkioulidou, M.; Ukhorskiy, A.; Mitchell, D.; Takahashi, K.; Lanzerotti, L.; Kletzing, C.; Spence, H.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025557 deep inside geosynchronous orbit; dipolarizations; Ion injections; ion species; Van Allen Probes |
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Statistical investigation of the efficiency of EMIC waves in precipitating relativistic electrons Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause Relativistic Electron Precipitation (REP). In our study, we carry out 4 years of analysis from 2013 to 2016, with relativistic electron precipitation spikes obtained from POES satellites and EMIC waves observation from Van Allen Probes. Among the 473 coincidence events when POES satellites go through the region conjugate to EMIC wave activity, only 127 are associated with REP. Additionally, the coincidence occurrence rate is about 10\% higher than the random coincidence occurrence rate, indicating that EMIC waves and relativistic electrons can be statistically related, but the link is weaker than expected. H+ band EMIC waves have been regarded as less important than He+ band EMIC waves for the precipitation of relativistic electrons. We demonstrate that the proportion of H+ band EMIC wave events that are associated with REP (22\% to 32\%) is slightly higher than for He+ band EMIC wave activity (18\% to 27\%). An even greater proportion (25\% to 40\%) of EMIC waves are accompanied by REP events when H+ band and He+ band EMIC waves occur simultaneously. Qin, Murong; Hudson, Mary; Millan, Mary; Woodger, Leslie; Shekhar, Sapna; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025419 causally related; coincidence occurrence rate; efficiency; EMIC wave; random coincidence occurrence rate; relativistic electron precipitation; Van Allen Probes |
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The transport mechanism of the ring current ions differs among ion energies. Lower-energy (≲150 keV) ions are well known to be transported convectively. Higher-energy (≳150 keV) protons are reported to be transported diffusively, while there are few reports about transport of higher-energy oxygen ions. We report the radial transport of higher-energy oxygen ions into the deep inner magnetosphere during the late main phase of the magnetic storm on 23\textendash25 April 2013 observed by the Van Allen Probes spacecraft. An enhancement of 1\textendash100 mHz magnetic fluctuations is simultaneously observed. Observations of 3 and 30 mHz geomagnetic pulsations indicate the azimuthal mode number is <=10. The fluctuations can resonate with the drift and bounce motions of the oxygen ions. The results suggest that the combination of the drift and drift-bounce resonances is responsible for the radial transport of higher-energy oxygen ions. Mitani, K.; Seki, K.; Keika, K.; Gkioulidou, M.; Lanzerotti, L.; Mitchell, D.; Kletzing, C.; Published by: Geophysical Research Letters Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2018GL077500 |
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Based on over 4 years of Van Allen Probes measurements, an empirical model of radiation belt electron equatorial pitch angle distribution (PAD) is constructed. The model, developed by fitting electron PADs with Legendre polynomials, provides the statistical PADs as a function of L-shell (L=1 \textendash 6), magnetic local time (MLT), electron energy (~30 keV \textendash 5.2 MeV), and geomagnetic activity (represented by the Dst index), and is also the first empirical PAD model in the inner belt and slot region. For MeV electrons, model results show more significant day-night PAD asymmetry of electrons with higher energies and during disturbed times, which is caused by geomagnetic field configuration and flux radial gradient changes. Steeper PADs with higher fluxes around 90\textdegree pitch angle (PA) and lower fluxes at lower PAs for higher energy electrons and during active times are also present, which could be due to EMIC wave scattering. For 100s of keV electrons, cap PADs are generally present in the slot region during quiet times and their energy-dependent features are consistent with hiss wave scattering, while during active times, cap PADs are less significant especially at outer part of slot region, which could be due to the complex energizing and transport processes. 90\textdegree-minimum PADs are persistently present in the inner belt and appear in the slot region during active times, and minima at 90\textdegree PA are more significant for electrons with higher energies, which could be a critical evidence in identifying the underlying physical processes responsible for the formation of 90\textdegree-minimum PADs. Zhao, H.; Friedel, R.; Chen, Y.; Reeves, G.; Baker, D.; Li, X.; Jaynes, A.; Kanekal, S.; Claudepierre, S.; Fennell, J.; Blake, J.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2018 YEAR: 2018 DOI: 10.1029/2018JA025277 Empirical Model; Geomagnetic storms; inner belt and slot region; Pitch angle distribution; radiation belt electrons; Van Allen Probes |
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A poloidal Pc4 wave and proton flux oscillations are observed in the inner magnetosphere on the dayside near the magnetic equator by the Van Allen Probes spacecraft on 2 March 2014. The flux oscillations are observed in the energy range of 67.0 keV to 268.8 keV with the same frequency of the poloidal Pc4 wave. We find pitch angle and energy dispersion in the phase difference between the poloidal magnetic field and the proton flux oscillations, which are features of drift-bounce resonance. We estimate the resonance energy to be ~120 keV for pitch angle (α) of 30\textdegree or 150\textdegree, and 170\textendash180 keV for α = 50\textdegree or 130\textdegree. To examine the direction of energy flow between protons and the wave, we calculate the sign of the gradient of proton phase space density (df/dW) on both the inbound and outbound legs of the orbit. We find the gradient to be outward on both legs, which means that energy is transferred from the protons to the wave. During the poloidal Pc4 wave event, the Dst* index shows a measurable increase of ~6.7 nT. We estimate the total energy loss of the ring current from the recovery of the Dst* index and from the variation of proton flux by the drift-bounce resonance. We suggest that energy transfer from the ring current protons to the poloidal Pc4 wave via the drift-bounce resonance contributes to up to ~85 \% of the increase of the Dst* index. Oimatsu, S.; e, M.; Takahashi, K.; Yamamoto, K.; Keika, K.; Kletzing, C.; Smith, C.; MacDowall, R.; Mitchell, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2018 YEAR: 2018 DOI: 10.1029/2017JA025087 |