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Found 28 entries in the Bibliography.
Showing entries from 1 through 28
| 2021 |
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Realistic electron diffusion rates and lifetimes due to scattering by electron holes AbstractPlasma sheet electron precipitation into the diffuse aurora is critical for magnetosphere-ionosphere coupling. Recent studies have shown that electron phase space holes can pitch-angle scatter electrons and may produce plasma sheet electron precipitation. These studies have assumed identical electron hole parameters to estimate electron scattering rates (Vasko et al., 2018). In this study, we have re-evaluated the efficiency of this scattering by incorporating realistic electron hole properties from direct spacecraft observations into computing electron diffusion rates and lifetimes. The most important electron hole properties in this evaluation are their distributions in velocity and spatial scale and electric field root-mean-square intensity (). Using direct measurements of electron holes during a plasma injection event observed by the Van Allen Probe at , we find that when 4 mV/m electron lifetimes can drop below one hour and are mostly within strong diffusion limits at energies below 10 keV. During an injection observed by the THEMIS spacecraft at , electron holes with even typical intensities (1 mV/m) can deplete low-energy (a few keV) plasma sheet electrons within tens of minutes following injections and convection from the tail. Our results confirm that electron holes are a significant contributor to plasma sheet electron precipitation during injections. Shen, Yangyang; Vasko, Ivan; Artemyev, Anton; Malaspina, David; Chu, Xiangning; Angelopoulos, Vassilis; Zhang, Xiao-Jia; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029380 diffuse aurora; electron pitch-angle scattering; electron phase space hole; Wave-particle interaction; electron lifetimes; broadband electrostatic fluctuations; Van Allen Probes |
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Global Survey of Electron Precipitation due to Hiss Waves in the Earth s Plasmasphere and Plumes Abstract We present a global survey of energetic electron precipitation from the equatorial magnetosphere due to hiss waves in the plasmasphere and plumes. Using Van Allen Probes measurements, we calculate the pitch angle diffusion coefficients at the bounce loss cone, and evaluate the energy spectrum of precipitating electron flux. Our ∼6.5-year survey shows that, during disturbed times, hiss inside the plasmasphere primarily causes the electron precipitation at L > 4 over 8 h < MLT < 18 h, and hiss waves in plumes cause the precipitation at L > 5 over 8 h < MLT < 14 h and L > 4 over 14 h < MLT < 20 h. The precipitating energy flux increases with increasing geomagnetic activity, and is typically higher in the plasmaspheric plume than the plasmasphere. The characteristic energy of precipitation increases from ∼20 keV at L = 6 to ∼100 keV at L = 3, potentially causing the loss of electrons at several hundred keV. Ma, Q.; Li, W.; Zhang, X.-J.; Bortnik, J.; Shen, X.-C.; Connor, H.; Boyd, A.; Kurth, W.; Hospodarsky, G.; Claudepierre, S.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029644 electron precipitation; hiss wave; plasmasphere; plasmaspheric plume; Precipitating Energy Flux; Van Allen Probes Survey; Van Allen Probes |
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Abstract We investigate relativistic electron precipitation events detected by POES in low-Earth orbit in close conjunction with Van Allen Probe A observations of EMIC waves near the geomagnetic equator. We show that the occurrence rate of > 0.7 MeV electron precipitation recorded by POES during those times strongly increases, reaching statistically significant levels when the minimum electron energy for cyclotron resonance with hydrogen or helium band EMIC waves at the equator decreases below ≃ 1.0 − 2.5 MeV, as expected from quasi-linear theory. Both hydrogen and helium band EMIC waves can be effective in precipitating MeV electrons. However, > 0.7 MeV electron precipitation is more often observed (at statistically significant levels) when the minimum electron energy for cyclotron resonance with hydrogen band waves is low (Emin = 0.6 − 1.0 MeV), whereas it is more often observed when the minimum electron energy for cyclotron resonance with helium band waves is slightly larger (Emin = 1.0 − 2.5 MeV), indicative of warm plasma effects for waves approaching the He+ gyrofrequency. We further show that most precipitation events had energies > 0.7 − 1.0 MeV, consistent with the estimated minimum energy (Emin ∼ 0.6 − 2.5 MeV) of cyclotron resonance with the observed EMIC waves during the majority of these events. However, 4 out of the 12 detected precipitation events cannot be explained by electron quasi-linear scattering by the observed EMIC waves, and 12 out of 20 theoretically expected precipitation events were not detected by POES, suggesting the possibility of nonlinear effects likely present near the magnetic equator, or warm plasma effects, and/or narrowly localized bursts of EMIC waves. This article is protected by copyright. All rights reserved. Zhang, X.-J.; Mourenas, D.; Shen, X.-C.; Qin, M.; Artemyev, A.; Ma, Q.; Li, W.; Hudson, M.; Angelopoulos, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029193 EMIC waves; relativistic electron precipitation; minimum resonant energy; Van Allen Probes; POES; Radiation belts |
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Determining the Temporal and Spatial Coherence of Plasmaspheric Hiss Waves in the Magnetosphere Abstract Plasmaspheric hiss is one of the most important plasma waves in the Earth s magnetosphere to contribute to radiation belt dynamics by pitch-angle scattering energetic electrons via wave-particle interactions. There is growing evidence that the temporal and spatial variability of wave-particle interactions are important factors in the construction of diffusion-based models of the radiation belts. Hiss amplitudes are thought to be coherent across large distances and on long timescales inside the plasmapause, which means that hiss can act on radiation belt electrons throughout their drift trajectories for many hours. In this study, we investigate both the spatial and temporal coherence of plasmaspheric hiss between the two Van Allen Probes from November 2012 to July 2019. We find ∼3,264 events where we can determine the correlation of wave amplitudes as a function of both spatial distance and time lag in order to study the spatial and temporal coherence of plasmaspheric hiss. The statistical results show that both the spatial and temporal correlation of plasmaspheric hiss decrease with increasing L-shell, and become incoherent at L > ∼4.5. Inside of L = ∼4.5, we find that hiss is coherent to within a spatial extent of up to ∼1,500 km and a time lag up to ∼10 min. We find that the spatial and temporal coherence of plasmaspheric hiss does not depend strongly on the geomagnetic index (AL*) or magnetic local time. We discuss the ramifications of our results with relevance to understanding the global characteristics of plasmaspheric hiss waves and their role in radiation belt dynamics. Zhang, Shuai; Rae, Jonathan; Watt, Clare; Degeling, Alexander; Tian, Anmin; Shi, Quanqi; Shen, Xiao-Chen; Smith, Andy; Wang, Mengmeng; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028635 |
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Periodic Rising and Falling Tone ECH Waves from Van Allen Probes Observations AbstractElectron cyclotron harmonic (ECH) waves are known to precipitate plasma sheet electrons into the upper atmosphere and generate diffuse aurorae. In this study, we report quasi-periodic rising (3 events) and falling tone (22 events) ECH waves observed by Van Allen Probes, and evaluate their properties. These rising and falling tone ECH waves prefer to occur during quiet geomagnetic conditions over the dusk to midnight sector in relatively high-density (10–80 cm-3) regions. Their repetition periods increase with increasing L shell at L < 6, ranging from ∼60 to 110 s. The wave element duration varies from 10 s to 130 s peaking at ∼40 s and the chirping rate peaks at ∼50 (∼-50) Hz/s for rising (falling) tones. Our findings reveal intriguing features of the ECH wave properties, which provide new insights into their generation and potential effects on electron precipitation. Shen, Xiao-Chen; Li, Wen; Ma, Qianli; Published by: Geophysical Research Letters Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020GL091330 ECH wave; falling tone; rising tone; Magnetosphere; plasma wave; Van Allen Probes |
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AbstractThe two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 hours. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies were close to but did not exactly match the repetition frequency of QP emissions for most of the time, suggesting that those coherent QP emissions probably originated from a common source, which then propagated over a broad area in the magnetosphere. The QP emissions were amplified by local anisotropic electron distributions, and their large-scale amplitudes were modulated by the plasma density. A novel observation of this event is that chorus waves at frequencies above QP emissions exhibit a strong correlation with QP emissions. Those chorus waves intensified when the QP emissions reach their peak frequency. This indicates that embryonic QP emissions may be critical for its own intensification as well as chorus waves under certain circumstances. The low-earth-orbit POES satellite observed enhanced energetic electron precipitation in conjunction with the Van Allen Probes, providing direct evidence that QP emissions precipitate energetic electrons into the atmosphere. This scenario is quantitatively confirmed by our quasilinear diffusion simulation results. Li, Jinxing; Bortnik, Jacob; Ma, Qianli; Li, Wen; Shen, Xiaochen; Nishimura, Yukitoshi; An, Xin; Thaller, Scott; Breneman, Aaron; Wygant, John; Kurth, William; Hospodarsky, George; Hartley, David; Reeves, Geoffrey; Funsten, Herbert; Blake, Bernard; Spence, Harlan; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028484 quasiperiodic emissions; electron precipitation; Radiation belt; chorus waves; Van Allen Probes; ULF wave |
| 2020 |
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Lightning generated whistlers (LGWs) play an important role in precipitating energetic electrons in the Earth s inner radiation belt and beyond. Wave burst data from the Van Allen Probes are used to unambiguously identify LGWs and analyze their properties at L < 4 by extending their frequencies down to ~100 Hz for the first time. The statistical results show that LGWs typically occur at frequencies from 100 Hz to 10 kHz with the major wave power below the equatorial lower hybrid resonance frequency, and their wave amplitudes are typically strong at L < 3 with an occurrence rate up to ~30\% on the nightside. The lifetime calculation indicates that LGWs play an important role in scattering electrons from tens of keV to several MeV at L < ~2.5. Our newly constructed LGW models are critical for evaluating the global effects of LGWs on energetic electron loss at L < 4. Green, A.; Li, W.; Ma, Q.; Shen, X.-C.; Bortnik, J.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 08/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL089584 lightning generated whistlers; electron precipitation; Inner radiation belt; hiss; VLF transmitter waves; global distribution; Van Allen Probes |
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Whistler mode chorus waves can scatter plasma sheet electrons into the loss cone and produce the Earth s diffuse aurora. Van Allen Probes observed plasma sheet electron injections and intense chorus waves on 24 November 2012. We use quasilinear theory to calculate the precipitating electron fluxes, demonstrating that the chorus waves could lead to high differential energy fluxes of precipitating electrons with characteristic energies of 10–30 keV. Using this method, we calculate the precipitating electron flux from 2012 to 2019 when the Van Allen Probes were near the magnetic equator and perform global surveys of electron precipitation under different geomagnetic conditions. The most significant electron precipitation due to chorus is found from the nightside to dawn sectors over 4 < L < 6.5. The average total precipitating energy flux is enhanced during disturbed conditions, with time-averaged values reaching ~3–10 erg/cm2/s when AE ≥ 500 nT. Ma, Q.; Connor, H.; Zhang, X.-J.; Li, W.; Shen, X.-C.; Gillespie, D.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Claudepierre, S.; Reeves, G.; Spence, H.; Published by: Geophysical Research Letters Published on: 07/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088798 Chorus wave; electron precipitation; plasma sheet electron; Van Allen Probes observation; Van Allen Probes |
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Global Model of Whistler Mode Chorus in the Near-Equatorial Region (|λm|< 18°) We extend our database of whistler mode chorus, based on data from seven satellites, by including ∼3 years of data from Radiation Belt Storm Probes (RBSP)-A and RBSP-B and an additional ∼6 years of data from Time History of Events and Macroscale Interactions during Substorms (THEMIS)-A, THEMIS-D, and THEMIS-E. The new database allows us to probe the near-equatorial region in detail, revealing new features. In the equatorial source region, |λm|<6°, strong wave power is most extensive in the 0.1–0.4fce bands in the region 21–11 magnetic local time (MLT) from the plasmapause out to L∗ = 8 and beyond, especially near dawn. At higher frequencies, in the 0.4–0.6fce frequency bands, strong wave power is more tightly confined, typically being restricted to the postmidnight sector in the region 4 Meredith, Nigel; Horne, Richard; Shen, Xiao-Chen; Li, Wen; Bortnik, Jacob; Published by: Geophysical Research Letters Published on: 05/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL087311 whistler mode chorus; wave-particle interactions; Radiation belts; Van Allen Probes |
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Statistical Dependence of EMIC Wave Scattering on Wave and Plasma Parameters Abstract A recent statistical study (Qin et al., 2018, https://doi.org/10.1029/2018JA025419) has suggested that not all electromagnetic ion cyclotron (EMIC) waves can scatter relativistic electrons. However, knowledge of the factors that influence the EMIC wave scattering efficiency is still limited in observations. In our study, we perform 6 years of analysis of data from 2013 to 2018, with relativistic electron precipitation (REP) observed by POES and EMIC wave observations from Van Allen Probes. The coincidence occurrence rate between EMIC waves and relativistic electron precipitation events is about 34\%. Proportion of different bands of EMIC wave events that are associated with REP is as follows: H+ band and He+ band waves occurring simultaneously >H+ band >He+ band occurrence, same as in our previous study (Qin et al., 2018, https://doi.org/10.1029/2018JA025419). It is also found that the coincidence occurrence rate of EMIC wave events and REP events increases with respect to increased background plasma density, with increases in the ratio of plasma frequency to local gyrofrequency, increasing EMIC wave power and when the wave frequency approaches the gyrofrequency. The dependence on background electron density is stronger than the dependence on the ratio of plasma frequency to gyrofrequency. The coincidence occurrence rate decreases as the magnetic field increases between 120 and 270 nT, consistent with a previous study. These results are critical for better understanding and predicting the REP into the upper atmosphere due to EMIC waves. Qin, Murong; Hudson, Mary; Millan, Robyn; Woodger, Leslie; Shen, Xiaochen; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2020 DOI: 10.1029/2020JA027772 EMIC waves; relativistic electron precipitation; coincidence occurrence rate; parametric dependence; Van Allen Probes |
| 2019 |
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Direct Observation of Subrelativistic Electron Precipitation Potentially Driven by EMIC Waves Electromagnetic ion cyclotron (EMIC) waves are known to typically cause electron losses into Earth\textquoterights upper atmosphere at >~1 MeV, while the minimum energy of electrons subject to efficient EMIC-driven precipitation loss is unresolved. This letter reports electron precipitation from subrelativistic energies of ~250 keV up to ~1 MeV observed by the Focused Investigations of Relativistic Electron Burst Intensity, Range and Dynamics (FIREBIRD-II) CubeSats, while two Polar Operational Environmental Satellites (POES) observed proton precipitation nearby. Van Allen Probe A detected EMIC waves (~0.7\textendash2.0 nT) over the similar L shell extent of electron precipitation observed by FIREBIRD-II, albeit with a ~1.6 magnetic local time (MLT) difference. Although plasmaspheric hiss and magnetosonic waves were also observed, quasi-linear calculations indicate that EMIC waves were the most efficient in driving the electron precipitation. Quasi-linear theory predicts efficient precipitation at >0.8\textendash1 MeV (due to H-band EMIC waves), suggesting that other mechanisms are required to explain the observed subrelativistic electron precipitation. Capannolo, L.; Li, W.; Ma, Q.; Chen, L.; Shen, X.-C.; Spence, H.; Sample, J.; Johnson, A.; Shumko, M.; Klumpar, D.; Redmon, R.; Published by: Geophysical Research Letters Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019GL084202 electron precipitation; EMIC waves; FIREBIRD-II; quasi linear theory; Radiation belts; Van Allen Probes; wave particle interactions |
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Characteristics and Generation of Low-Frequency Magnetosonic Waves Below the Proton Gyrofrequency We report a Van Allen Probes observation of large-amplitude magnetosonic waves with the peak intensity below the proton gyrofrequency (fcp), which may potentially be misinterpreted as electromagnetic ion cyclotron waves. The frequency spacing of the wave harmonic structure suggests that these magnetosonic waves are excited at a distant source region and propagate radially inward. We also conduct a statistical analysis of low-frequency magnetosonic waves below fcp based on the Van Allen Probes data from October 2012 to December 2018. The spatial distribution shows that these low-frequency magnetosonic emissions are dominantly observed inside the plasmasphere from the prenoon to the midnight sector within 5\textdegree of the geomagnetic equator and typically have modest-to-strong wave amplitudes ranging from tens of pT to hundreds of pT. Our study provides insight into understanding the generation and propagation of these low-frequency magnetosonic waves in the Earth\textquoterights inner magnetosphere. Teng, Shangchun; Li, Wen; Tao, Xin; Ma, Qianli; Shen, Xiaochen; Published by: Geophysical Research Letters Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019GL085372 Below the proton gyrofrequency; Low frequency magnetosonic wave; Van Allen Probes; wave generation; Wave propagation characteristics |
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Modeling the Electron Flux Enhancement and Butterfly Pitch Angle Distributions on L Shells <2.5 We analyze an energetic electron flux enhancement event in the inner radiation belt observed by Van Allen Probes during an intense geomagnetic storm. The energetic electron flux at L~1.5 increased by a factor of 3 with pronounced butterfly pitch angle distributions (PADs). Using a three-dimensional radiation belt model, we simulate the electron evolution under the impact of radial diffusion, local wave-particle interactions including hiss, very low frequency transmitters, and magnetosonic waves, as well as Coulomb scattering. Consistency between observation and simulation suggests that inward radial diffusion plays a dominant role in accelerating electrons up to 900 keV and transporting the butterfly PADs from higher L shells to form the butterfly PADs at L~1.5. However, local wave-particle interactions also contribute to drive butterfly PADs at L ≳ 1.9. Our study provides a feasible mechanism to explain the electron flux enhancement in the inner belt and the persistent presence of the butterfly PADs at L~1.5. Hua, Man; Li, Wen; Ma, Qianli; Ni, Binbin; Nishimura, Yukitoshi; Shen, Xiao-Chen; Li, Haimeng; Published by: Geophysical Research Letters Published on: 09/2019 YEAR: 2019 DOI: 10.1029/2019GL084822 3-D radial belt modeling; Butterfly pitch angle distribution; Electron flux enhancement; inner belt and slot region; Inward radial diffusion; local wave-particle interactions; Van Allen Probes |
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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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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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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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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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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 |
| 2017 |
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Simulated prompt acceleration of multi-MeV electrons by the 17 March 2015 interplanetary shock Prompt enhancement of relativistic electron flux at L = 3-5 has been reported from Van Allen Probes Relativistic Electron Proton Telescope (REPT) measurements associated with the 17 March 2015 interplanetary shock compression of the dayside magnetosphere. Acceleration by \~ 1 MeV is inferred on less than a drift time scale as seen in prior shock compression events, which launch a magetosonic azimuthal electric field impulse tailward. This impulse propagates from the dayside around the flanks accelerating electrons in drift resonance at the dusk flank. Such longitudinally localized acceleration events produce a drift echo signature which was seen at >1 MeV energy on both Van Allen Probe spacecraft, with sustained observations by Probe B outbound at L = 5 at 2100 MLT at the time of impulse arrival, measured by the Electric Fields and Waves instrument. MHD-test particle simulations are presented which reproduce drift echo features observed in the REPT measurements at Probe B, including the energy and pitch angle dependence of drift echoes observed. While the flux enhancement was short-lived for this event due to subsequent inward motion of the magnetopause, stronger events with larger electric field impulses, as observed in March 1991 and the Halloween 2003 storm, produce enhancements which can be quantified by the inward radial transport and energization determined by the induction electric field resulting from dayside compression. Hudson, Mary; Jaynes, Allison; Kress, Brian; Li, Zhao; Patel, Maulik; Shen, Xiaochen; Thaller, Scott; Wiltberger, Michael; Wygant, John; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2017 YEAR: 2017 DOI: 10.1002/2017JA024445 17 March 2015; MeV electron acceleration; Radiation belt; test-particle simulation; Van Allen Probes |
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CME- or CIR-driven storms can change the electron distributions in the radiation belt dramatically, which can in turn affect the spacecraft in this region or induce geomagnetic effects. The Van Allen Probes twin spacecraft, launched on 30 August 2012, orbit near the equatorial plane and across a wide range of L* with apogee at 5.8 RE and perigee at 620 km. Electron data from Van Allen Probes MagEIS and REPT instruments have been binned every six hours at L*=3 (defined as 2.5 Shen, Xiao-Chen; Hudson, Mary; Jaynes, Allison; Shi, Quanqi; Tian, Anmin; Claudepierre, Seth; Qin, Mu-Rong; Zong, Qiu-Gang; Sun, Wei-Jie; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2017 YEAR: 2017 DOI: 10.1002/2017JA024100 CIR-driven storm; CME-driven storm; outer radiation belt; Van Allen Probes |
| 2016 |
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A new method to study the time correlation between Van Allen Belt electrons and earthquakes A new method to study a possible temporal correlation between hundreds of keV Van Allen Belt electrons and strong earthquakes is proposed. It consists in measuring the electrons pitch angle distribution (PAD), searching for PAD disturbances, and studying the time correlation between these PAD disturbances and strong earthquakes, occurring within a defined time window. The method was applied to measurements of energetic electrons, which were performed with the Energetic Particle, Composition, and Thermal Plasma (ECT)-MagEIS detector on board the Van Allen Probes (VAPs) mission and strong continental earthquakes, with magnitude M 5.0 and hypocenter depth 100 km. We report the correlation studies for electrons with energies of about 350 keV, with which a 3.84 standard deviations correlation peak was found at hour time bin, and about 450 keV with which no correlation peaks above 2.0 standard deviations were found. Our work proves the feasibility of the proposed method and the obtained results add useful and additional information with respect to past studies. Tao, Dan; Battiston, Roberto; Vitale, Vincenzo; Burger, William; Lazzizzera, Ignazio; Cao, Jinbin; Shen, Xuhui; Published by: International Journal of Remote Sensing Published on: 10/2016 YEAR: 2016 DOI: 10.1080/01431161.2016.1239284 |
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Frequency distribution is a vital factor in determining the contribution of whistler-mode chorus to radiation belt electron dynamics. Chorus is usually considered to occur in the frequency range 0.1\textendash0.8 inline image (with the equatorial electron gyrofrequency inline image). We here report an event of intense low-frequency chorus with nearly half of wave power distributed below 0.1 inline image observed by Van Allen Probe A on 27 August 2014. This emission propagated quasi-parallel to the magnetic field and exhibited hiss-like signatures most of the time. The low-frequency chorus can produce the rapid loss of low-energy (\~0.1 MeV) electrons, different from the normal chorus. For high-energy (>=0.5 MeV) electrons, the low-frequency chorus can yield comparable momentum diffusion to that of the normal chorus, but much stronger (up to 2 orders of magnitude) pitch-angle diffusion near the loss cone. Gao, Zhonglei; Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Shen, Chao; Wang, Shui; Published by: Geophysical Research Letters Published on: 02/2016 YEAR: 2016 DOI: 10.1002/2016GL067687 Cyclotron resonance; Hiss-like band; Low-frequency chorus; Radiation belt; Van Allen Probes; Rising tones; Van Allen Probes |
| 2015 |
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Disappearance of plasmaspheric hiss following interplanetary shock Plasmaspheric hiss is one of the important plasma waves controlling radiation belt dynamics. Its spatiotemporal distribution and generation mechanism are presently the object of active research. We here give the first report on the shock-induced disappearance of plasmaspheric hiss observed by the Van Allen Probes on 8 October 2013. This special event exhibits the dramatic variability of plasmaspheric hiss and provides a good opportunity to test its generation mechanisms. The origination of plasmaspheric hiss from plasmatrough chorus is suggested to be an appropriate prerequisite to explain this event. The shock increased the suprathermal electron fluxes, and then the enhanced Landau damping promptly prevented chorus waves from entering the plasmasphere. Subsequently, the shrinking magnetopause removed the source electrons for chorus, contributing significantly to the several-hours-long disappearance of plasmaspheric hiss. Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Shen, Chao; Zhang, Min; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Wygant, J.; Published by: Geophysical Research Letters Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2015GL063906 Cyclotron instability; Cyclotron resonance; interplanetary shock; Landau damping; Plasmaspheric Hiss; Radiation belt; Van Allen Probes |
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Exohiss waves are whistler mode hiss observed in the plasmatrough region. We present a case study of exohiss waves and the corresponding background plasma distributions observed by the Van Allen Probes in the dayside low-latitude region. The analysis of wave Poynting fluxes, suprathermal electron fluxes and cold electron densities supports the scenario that exohiss leaks from the plasmasphere into the plasmatrough. Quasilinear calculations further reveal that exohiss can potentially cause the resonant scattering loss of radiation belt electrons ~ Zhu, Hui; Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Shen, Chao; Xian, Tao; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Published by: Geophysical Research Letters Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014GL062964 Cyclotron resonance; Exohiss; Landau damping; Plasmaspheric Hiss; Radiation belt electron loss; Van Allen Probes |
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We study the rapid outward extension of the electron radiation belt on a timescale of several hours during three events observed by RBSP and THEMIS satellites, and particularly quantify the contributions of substorm injections and chorus waves to the electron flux enhancement near the outer boundary of radiation belt. A comprehensive analysis including both observations and simulations is performed for the first event on 26 May 2013. The outer boundary of electron radiation belt moved from L = 5.5 to L > 6.07 over about 6 hours, with up to four orders of magnitude enhancement in the 30 keV-5 MeV electron fluxes at L = 6. The observations show that the substorm injection can cause 100\% and 20\% of the total subrelativistic (~0.1 MeV) and relativistic (2-5 MeV) electron flux enhancements within a few minutes. The data-driven simulation supports that the strong chorus waves can yield 60\%-80\% of the total energetic (0.2-5.0 MeV) electron flux enhancement within about 6 hours. Some simple analyses are further given for the other two events on 2 and 29 June 2013, in which the contributions of substorm injections and chorus waves are shown to be qualitatively comparable to those for the first event. These results clearly illustrate the respective importance of substorm injections and chorus waves for the evolution of radiation belt electrons at different energies on a relatively short timescale. Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Zong, Q.-G.; He, Zhaoguo; Shen, Chao; Zhang, Min; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020709 Chorus wave; Electron acceleration; Radiation belt; substorm injection; Van Allen Probes; Wave-particle interaction |
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Local acceleration driven by whistler mode chorus waves largely accounts for the enhancement of radiation belt relativistic electron fluxes, whose favored region is usually considered to be the plasmatrough with magnetic local time approximately from midnight through dawn to noon. On 2 October 2013, the Van Allen Probes recorded a rarely reported event of intense duskside lower band chorus waves (with power spectral density up to 10-3nT2/Hz) in the low-latitude region outside of L=5. Such chorus waves are found to be generated by the substorm-injected anisotropic suprathermal electrons and have a potentially strong acceleration effect on the radiation belt energetic electrons. This event study demonstrates the possibility of broader spatial regions with effective electron acceleration by chorus waves than previously expected. For such intense duskside chorus waves, the occurrence probability, the preferential excitation conditions, the time duration, and the accurate contribution to the long-term evolution of radiation belt electron fluxes may need further investigations in future. Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; He, Zhaoguo; Shen, Chao; Shen, Chenglong; Wang, C.; Liu, Rui; Zhang, Min; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.610.1002/2014JA019919 |
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Local acceleration driven by whistler mode chorus waves largely accounts for the enhancement of radiation belt relativistic electron fluxes, whose favored region is usually considered to be the plasmatrough with magnetic local time approximately from midnight through dawn to noon. On 2 October 2013, the Van Allen Probes recorded a rarely reported event of intense duskside lower band chorus waves (with power spectral density up to 10-3nT2/Hz) in the low-latitude region outside of L=5. Such chorus waves are found to be generated by the substorm-injected anisotropic suprathermal electrons and have a potentially strong acceleration effect on the radiation belt energetic electrons. This event study demonstrates the possibility of broader spatial regions with effective electron acceleration by chorus waves than previously expected. For such intense duskside chorus waves, the occurrence probability, the preferential excitation conditions, the time duration, and the accurate contribution to the long-term evolution of radiation belt electron fluxes may need further investigations in future. Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; He, Zhaoguo; Shen, Chao; Shen, Chenglong; Wang, C.; Liu, Rui; Zhang, Min; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.610.1002/2014JA019919 |
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Nonstorm time dynamics of electron radiation belts observed by the Van Allen Probes Storm time electron radiation belt dynamics have been widely investigated for many years. Here we present a rarely reported nonstorm time event of electron radiation belt evolution observed by the Van Allen Probes during 21\textendash24 February 2013. Within 2 days, a new belt centering around L=5.8 formed and gradually merged with the original outer belt, with the enhancement of relativistic electron fluxes by a factor of up to 50. Strong chorus waves (with power spectral density up to 10-4nT2/Hz) occurred in the region L>5. Taking into account the local acceleration driven by these chorus waves, the two-dimensional STEERB can approximately reproduce the observed energy spectrums at the center of the new belt. These results clearly illustrate the complexity of electron radiation belt behaviors and the importance of chorus-driven local acceleration even during the nonstorm times. Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; He, Zhaoguo; Zhu, Hui; Zhang, Min; Shen, Chao; Wang, Yuming; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Published by: Geophysical Research Letters Published on: 01/2014 YEAR: 2014 DOI: 10.1002/2013GL058912 |
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