Bibliography
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Found 36 entries in the Bibliography.
Showing entries from 1 through 36
| 2021 |
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Trapping and amplification of unguided mode EMIC waves in the radiation belt AbstractElectromagnetic ion cyclotron (EMIC) waves can cause the scattering loss of the relativistic electrons in the radiation belt. They can be classified into the guided mode and the unguided mode, according to waves propagation behavior. The guided mode waves have been widely investigated in the radiation belt, but the observation of the unguided mode waves have not been expected. Based on the observations of Van Allen Probes, we demonstrate for the first time the existence of the intense unguided L-mode EMIC waves in the radiation belt according to the polarization characteristics. Growth rate analyses indicate that the hot protons with energies of a few hundred keV may provide the free energy for wave growth. The reflection interface formed by the spatial locations of local helium cutoff frequencies can be nearly parallel to the equatorial plane when the proton abundance ratio decreases sharply with -shell. This structure combined with hot protons may lead to the trapping and significant amplification of the unguided mode waves. These results may help to understand the nature of EMIC waves and their dynamics in the radiation belt. Wang, Geng; Gao, Zhonglei; Wu, MingYu; Wang, GuoQiang; Xiao, SuDong; Chen, YuanQiang; Zou, Zhengyang; Zhang, TieLong; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029322 EMIC waves; unguided mode; Radiation belt; ion abundance ratios; Wave trapping; growth rate; Van Allen Probes |
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ULF-modulation of whistler-mode waves in the inner magnetosphere during solar wind compression Abstract The solar wind plays important roles on terrestrial magnetosphere dynamics, including the particle population and plasma waves generation. Here we report an interesting event that ULF waves are enhanced right after solar wind compression and the compressional mode ULF wave subsequently modulates both the intensity and energy flux direction of whistler-mode waves. Quasi-periodic whistler-mode wave packets are observed around L=5.6 at noon sector by Van Allen Probes. Growth rate calculation demonstrates that the compressional mode ULF wave can modulate the whistler-mode wave intensity by modulating the energetic electron anisotropy. Moreover, the direction of wave energy flux is observed to alternate between northward and southward at equator, which is probably because the intense ULF waves periodically alter the relative direction of the wave source region respect to the spacecraft. The current results provide a chain of observational evidences to illustrate how the generation and propagation of whistler-mode waves in the inner magnetosphere are affected by ULF waves during the solar wind dynamic pressure enhancement. This article is protected by copyright. All rights reserved. Shang, Xiongjun; Liu, Si; Chen, Lunjin; Gao, Zhonglei; Wang, Geng; He, Qian; Li, Tong; Xiao, Fuliang; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029353 |
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Observation of unusual chorus elements by Van Allen Probes AbstractWhistler mode chorus waves play an important role in the radiation belt dynamics, which usually appear as discrete elements with frequency sweeping. Finer structure analysis shows that a chorus element is composed of several frequency-sweeping subelements, and such two-level structures can be successfully reproduced by modeling based on nonlinear theories. Previous observations and models suggest that an element and its subelements should have the same frequency-sweep direction. However, we here present two unexpected chorus rising tone events within which the subelements exhibit clearly reversed, falling frequency-sweep. Moreover, the subelements consist of several wave packets that also show falling frequency-sweep features. The three-level structured chorus elements are distinctly different from all the reported observations and seem to bring challenges to the existing theories. We propose a possible scenario that the falling tone subelements are formed by nonlinear process with much shorter timescale and the starting frequency of each subelement is controlled by fast varying electron distribution. This study may inspire more studies toward a thorough understanding of the chorus generation process. Liu, Si; Gao, Zhonglei; Xiao, Fuliang; He, Qian; Li, Tong; Shang, Xiongjun; Zhou, Qinghua; Yang, Chang; Zhang, Sai; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029258 |
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Abstract Auroral kilometric radiations (AKR) are strong radio emission phenomena, and can prduce significant acceleration or scattering of radiation belt electrons. The variation of AKR wave amplitude with the latitude (λ) has not been reported so far owing to lack of measurements. Here, using observations of the Arase satellite and Van Allen Probes from 23 March 2017 to 31 July 2019, we present the first statistical study on the AKR electric field amplitude (Et) in the radiation belts for |λ| = 0° − 40° and L-shell L = 3.0−6.2. Results (totally 14,770 samples) show that Et can be described by a concise formula: Et(λ) = E0 exp(ξ sin |λ|), decreasing with decreasing latitude. Fitting parameters E0 and ξ are limited in the ranges: E0 = 0.054−0.340 mV/m and ξ = 3.0−4.2. Wave amplitudes are greater (smaller) under intense (weak) geomagnetic conditions. This study helps to better quantify the gyroresonance between AKR and radiation belt electrons. Zhang, Sai; Liu, Si; Li, Wentao; He, Yihua; Yang, Qiwu; Xiao, Fuliang; Kumamoto, Atsushi; Miyoshi, Yoshizumi; Nakamura, Yosuke; Tsuchiya, Fuminori; Kasahara, Yoshiya; Shinohara, Iku; Published by: Geophysical Research Letters Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL092805 AKR; wave amplitude; geomagnetic latitude; Radiation belt; field-aligned; Van Allen Probes |
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Energetic electron detection packages on board Chinese navigation satellites in MEO Abstract Energetic electron measurements and spacecraft charging are of great significance for theoretical research in space physics and space weather applications. In this paper, the energetic electron detection package (EEDP) deployed on three Chinese navigation satellites in medium Earth orbit (MEO) is reviewed. The instrument was developed by the space science payload team led by Peking University. The EEDP includes a pinhole medium-energy electron spectrometer (MES), a high-energy electron detector (HED) based on ΔE-E telescope technology, and a deep dielectric charging monitor (DDCM). The MES measures the energy spectra of 50−600 keV electrons from nine directions with a 180°×30° field of view (FOV). The HED measures the energy spectrum of 0.5−3.0 MeV electrons from one direction with a 30° cone-angle FOV. The ground test and calibration results indicate that these three sensors exhibit excellent performance. Preliminary observations show that the electron spectra measured by the MES and HED are in good agreement with the results from the magnetic electron-ion spectrometer (MagEIS) of the Van Allen Probes spacecraft, with an average relative deviation of 27.3\% for the energy spectra. The charging currents and voltages measured by the DDCM during storms are consistent with the high-energy electron observations of the HED, demonstrating the effectiveness of the DDCM. The observations of the EEDP on board the three MEO satellites can provide important support for theoretical research on the radiation belts and the applications related to space weather. YuGuang, Ye; Hong, Zou; Qiu-Gang, Zong; HongFei, Chen; JiQing, Zou; WeiHong, Shi; XiangQian, Yu; WeiYing, Zhong; YongFu, Wang; YiXin, Hao; ZhiYang, Liu; XiangHong, Jia; Bo, Wang; XiaoPing, Yang; XiaoYun, Hao; Published by: Earth and Planetary Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.26464/epp2021021 Radiation belts; energetic electron detection; Pin-hole technology; Chinese navigation satellites; MEO; internal charging; Van Allen Probes |
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Energetic electron detection packages on board Chinese navigation satellites in MEO Abstract Energetic electron measurements and spacecraft charging are of great significance for theoretical research in space physics and space weather applications. In this paper, the energetic electron detection package (EEDP) deployed on three Chinese navigation satellites in medium Earth orbit (MEO) is reviewed. The instrument was developed by the space science payload team led by Peking University. The EEDP includes a pinhole medium-energy electron spectrometer (MES), a high-energy electron detector (HED) based on ΔE-E telescope technology, and a deep dielectric charging monitor (DDCM). The MES measures the energy spectra of 50−600 keV electrons from nine directions with a 180°×30° field of view (FOV). The HED measures the energy spectrum of 0.5−3.0 MeV electrons from one direction with a 30° cone-angle FOV. The ground test and calibration results indicate that these three sensors exhibit excellent performance. Preliminary observations show that the electron spectra measured by the MES and HED are in good agreement with the results from the magnetic electron-ion spectrometer (MagEIS) of the Van Allen Probes spacecraft, with an average relative deviation of 27.3\% for the energy spectra. The charging currents and voltages measured by the DDCM during storms are consistent with the high-energy electron observations of the HED, demonstrating the effectiveness of the DDCM. The observations of the EEDP on board the three MEO satellites can provide important support for theoretical research on the radiation belts and the applications related to space weather. YuGuang, Ye; Hong, Zou; Qiu-Gang, Zong; HongFei, Chen; JiQing, Zou; WeiHong, Shi; XiangQian, Yu; WeiYing, Zhong; YongFu, Wang; YiXin, Hao; ZhiYang, Liu; XiangHong, Jia; Bo, Wang; XiaoPing, Yang; XiaoYun, Hao; Published by: Earth and Planetary Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.26464/epp2021021 Radiation belts; energetic electron detection; Pin-hole technology; Chinese navigation satellites; MEO; internal charging; Van Allen Probes |
| 2020 |
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Fast magnetosonic (MS) waves are excited by the ring distribution of energetic protons preferably when the ring velocity (VR) is within a factor of 2 above or below the local Alfvén speed (VA). Here we examine the global distributions of MS waves and proton rings with 0.5VA ≤ VR ≤ 2VA based on 64 months (from October 25, 2012 to February 28, 2018) of Van Allen Probes observations. The statistical results show that MS waves are present over a broad region of L = 1.2–6.0 and 00–24 magnetic local time (MLT), with a higher occurrence rate at L = 2.5–5.5 on the dayside. Proton rings occur mainly on the dayside of L > 5.0. During active geomagnetic periods, both MS waves and proton rings occur more frequently and extend to low L-shells. The current results provide the further observational evidence that MS waves can be excited by proton rings at a distant region and propagate to low L-shells. Zhou, Qinghua; Jiang, Zheng; Yang, Chang; He, Yihua; Liu, Si; Xiao, Fuliang; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028354 Fast Magnetosonic Waves; global occurrences; proton ring distribution; Radiation belt; Van Allen Probe observation; Van Allen Probes |
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Relation Between Shock-Related Impulse and Subsequent ULF Wave in the Earth s Magnetosphere The generation of Pc4-5 ultralow frequency (ULF) waves after interplanetary shock-induced electric field impulses in the Earth s magnetosphere is studied using Van Allen Probes measurements by investigating the relationship between the first impulses and subsequent resonant ULF waves. In the dayside, the relevant time scales of the first impulse is correlated better with local Alfvén speed than with local eigenfrequency, implying that the temporal scale of the first impulse is more likely related to fast-mode wave propagation rather than local field line resonance. There are only 20 out of 51 events with narrow-band poloidal ULF waves induced after the first impulse, showing a higher chance for ULF wave generation at the locations where the impulse equivalent frequency scale matches the local eigenfrequency. It is suggested that the shock-related ULF wave can be excited in the magnetosphere on condition that shock-induced impulse has large enough amplitude with its frequency matching the local eigenfrequency. Zhang, Dianjun; Liu, Wenlong; Li, Xinlin; Sarris, Theodore; Wang, Yongfu; Xiao, Chao; Zhang, Zhao; Wygant, John; Published by: Geophysical Research Letters Published on: 11/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL090027 ULF wave; interplanetary shock; Magnetosphere; Field line resonance; electric field; wave excitation; Van Allen Probes |
| 2019 |
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Auroral kilometric radiation (AKR) can potentially produce serious damage to space-borne systems by accelerating trapped radiation belt electrons to relativistic energies. Here we examine the global occurrences of AKR emissions in radiation belts based on Van Allen Probes observations from 1 October 2012 to 31 December 2016. The statistical results (1,848 events in total) show that AKR covers a broad region of L= 3\textendash6.5 and 00\textendash24 magnetic local time (MLT), with a higher occurrence on the nightside (20\textendash24 MLT and 00\textendash04 MLT) within L= 5\textendash6.5. All the AKR events are observed to be accompanied with suprathermal (\~1 keV) electron flux enhancements. During active geomagnetic periods, both AKR occurrences and electron injections tend to be more distinct, and AKR emission extends to the dayside. The current study shows that AKR emissions from the remote sources are closely associated with electron injections. Zhao, Wanli; Liu, Si; Zhang, Sai; Zhou, Qinghua; Yang, Chang; He, Yihua; Gao, Zhonglei; Xiao, Fuliang; Published by: Geophysical Research Letters Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019GL083944 Auroral kilometric radiation; global occurrence; Radiation belt; suprathermal electron flux enhancenments; 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 |
| 2018 |
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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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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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Observations of impulsive electric fields induced by Interplanetary Shock We investigate the characteristics of impulsive electric fields in Earth\textquoterights magnetosphere, as measured by the Van Allen Probes, in association with interplanetary shocks, as measured by ACE and Wind spacecraft in the solar wind from January 2013 to July 2016. It is shown that electric field impulses are mainly induced by global compressions by the shocks, mostly in the azimuthal direction and the amplitudes of the initial electric field impulses are positively correlated with the rate of increase of dynamic pressure across the shock in the dayside. It is also shown that the temporal profile of the impulse is related to the temporal profile of the solar wind dynamic pressure, Pd. It is suggested that during the first period of the impulse the evolution of the electric field is directly controlled by external solar wind forcing, and thus finite rates of change of Pd should be considered in the study of the interactions between solar wind and magnetosphere. Implications of shock-induced impulsive electric fields on the acceleration and transport of radiation belt electrons are also discussed. Zhang, Dianjun; Liu, Wenlong; Li, Xinlin; Sarris, Theodore; Xiao, Chao; Wygant, J.; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL078809 electric field; inner magnetosphere; interplanetary shock; particle accelaration; Van Allen Probes |
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Previous studies have revealed a typical picture that seed electrons are transported inward under the drive of radial diffusion and then accelerated via chorus to relativistic energies. Here we show a potentially different process during the 2\textendash3 October 2013 storm when Van Allen Probes observed extremely rapid (by about 50 times in 2 h) flux enhancements of relativistic (1.8\textendash3.4 MeV) electrons but without distinct chorus at lower L-shells. Meanwhile, Time History of Events and Macroscale Interactions during Substorms satellites simultaneously measured enhanced chorus and fluxes of energetic (\~100\textendash300 keV) seed electrons at higher L-shells. Numerical calculations show that chorus can efficiently accelerate seed electrons at L \~ 8.3. Then radial diffusion further increased the phase space density of relativistic electrons throughout the outer radiation belts, with a remarkable agreement with the observation in magnitude and timescale. The current results provide a different physical scenario on the interplay between radial diffusion and local acceleration in outer radiation belt. Liu, Si; Yan, Qi; Yang, Chang; Zhou, Qinghua; He, Zhaoguo; He, Yihua; Gao, Zhonglei; Xiao, Fuliang; Published by: Geophysical Research Letters Published on: 02/2018 YEAR: 2018 DOI: 10.1002/grl.v45.310.1002/2017GL076513 chorus-driven acceleration; radial diffusion; Radiation belt; THEMIS; Van Allen Probes |
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During the 13-14 November 2012 storm, Van Allen Probe A simultaneously observed a 10-h period of enhanced chorus (including quasi-parallel and oblique propagation components) and relativistic electron fluxes over a broad range of L = 3-6 and MLT=2 - 10 within a complete orbit cycle. By adopting a Gaussian fit to the observed wave spectra, we obtain the wave parameters and calculate the bounce-averaged diffusion coefficients. We solve the Fokker-Planck diffusion equation to simulate flux evolutions of relativistic (1.8-4.2 MeV) electrons during two intervals when Probe A passed the location L = 4.3 along its orbit. The simulating results show that chorus with combined quasi-parallel and oblique components can produce a more pronounced flux enhancement in the pitch angle range \~45o-80o, consistent well with the observation. The current results provide the first evidence on how relativistic electron fluxes vary under the drive of almost continuously distributed chorus with both quasi-parallel and oblique components within a complete orbit of Van Allen Probe. Yang, Chang; Xiao, Fuliang; He, Yihua; Liu, Si; Zhou, Qinghua; Guo, Mingyue; Zhao, Wanli; Published by: Geophysical Research Letters Published on: 02/2018 YEAR: 2018 DOI: 10.1002/2017GL075894 energetic electron; Geomagnetic storm; outer radiation belt; Van Allen Probes; Wave-particle interaction; whistler-mode chorus wave |
| 2017 |
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Previous theoretical studies have shown that dayside chorus can produce butterfly distribution of energetic electrons in the Earth\textquoterights radiation belts by preferentially accelerating medium pitch angle electrons, but this requires the further confirmation from high-resolution satellite observation. Here, we report correlated Van Allen Probes data on wave and particle during the 11\textendash13 April, 2014 geomagnetic storm. We find that a butterfly pitch angle distribution of relativistic electrons is formed around the location L = 4.52, corresponding to the presence of enhanced dayside chorus. Using a Gaussian distribution fit to the observed chorus spectra, we calculate the bounce-averaged diffusion rates and solve two-dimensional Fokker-Planck equation. Numerical results demonstrate that acceleration by dayside chorus can yield the electron flux evolution both in the energy and butterfly pitch angle distribution comparable to the observation, providing a further evidence for the formation of butterfly distribution of relativistic electrons driven by very low frequency (VLF) plasma waves. Jin, YuYue; Yang, Chang; He, Yihua; Liu, Si; Zhou, Qinghua; Xiao, Fuliang; Published by: Science China Technological Sciences Published on: 09/2017 YEAR: 2017 DOI: 10.1007/s11431-017-9067-y butterfly distribution relativistic electrons radiation belts wave-particle interaction dayside chorus; Van Allen Probes |
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Electrostatic electron cyclotron harmonic (ECH) waves generated by the electron loss cone distribution can produce efficient scattering loss of plasma sheet electrons, which has a significant effect on the dynamics in the outer magnetosphere. Here we report two ECH emission events around the same location L≈ 5.7\textendash5.8, MLT ≈ 12 from Van Allen Probes on 11 February (event A) and 9 January 2014 (event B), respectively. The spectrum of ECH waves was centered at the lower half of the harmonic bands during event A, but the upper half during event B. The observed electron phase space density in both events is fitted by the subtracted bi-Maxwellian distribution, and the fitting functions are used to evaluate the local growth rates of ECH waves based on a linear theory for homogeneous plasmas. ECH waves are excited by the loss cone instability of 50 eV\textendash1 keV electrons in the lower half of harmonic bands in the low-density plasmasphere in event A, and 1\textendash10 keV electrons in the upper half of harmonic bands in a relatively high-density region in event B. The current results successfully explain observations and provide a first direct evidence on how ECH waves are generated in the lower and upper half of harmonic frequency bands. Zhou, Qinghua; Xiao, Fuliang; Yang, Chang; Liu, Si; He, Yihua; Baker, D.; Spence, H.; Reeves, G.; Funsten, H.; Published by: Geophysical Research Letters Published on: 05/2017 YEAR: 2017 DOI: 10.1002/2017GL073051 ECH waves; RBSP results; Van Allen Probes; Wave-particle interaction |
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Generation of extremely low frequency chorus in Van Allen radiation belts Recent studies have shown that chorus can efficiently accelerate the outer radiation belt electrons to relativistic energies. Chorus, previously often observed above 0.1 equatorial electron gyrofrequency fce, was generated by energetic electrons originating from Earth\textquoterights plasma sheet. Chorus below 0.1 fce has seldom been reported until the recent data from Van Allen Probes, but its origin has not been revealed so far. Because electron resonant energy can approach the relativistic level at extremely low frequency, relativistic effects should be considered in the formula for whistler mode wave growth rate. Here we report high-resolution observations during the 14 October 2014 small storm and firstly demonstrate, using a fully relativistic simulation, that electrons with the high-energy tail population and relativistic pitch angle anisotropy can provide free energy sufficient for generating chorus below 0.1 fce. The simulated wave growth displays a very similar pattern to the observations. The current results can be applied to Jupiter, Saturn, and other magnetized planets. Xiao, Fuliang; Liu, Si; Tao, Xin; Su, Zhenpeng; Zhou, Qinghua; Yang, Chang; He, Zhaoguo; He, Yihua; Gao, Zhonglei; Baker, D.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023561 ELF chorus waves; RBSP results; relativistic distribution; Van Allen Probes; Wave-particle interaction |
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Energetic (hundreds of keV) electrons in the radiation belt slot region have been found to exhibit the butterfly pitch angle distributions. Resonant interactions with magnetosonic and whistler-mode waves are two potential mechanisms for the formation of these peculiar distributions. Here we perform a statistical study of energetic electron pitch angle distribution characteristics measured by Van Allen Probes in the slot region during a three-year period from May 2013 to May 2016. Our results show that electron butterfly distributions are closely related to magnetosonic waves rather than to whistler-mode waves. Both electron butterfly distributions and magnetosonic waves occur more frequently at the geomagnetically active times than at the quiet times. In a statistical sense, more distinct butterfly distributions usually correspond to magnetosonic waves with larger amplitudes and vice versa. The averaged magnetosonic wave amplitude is less than 5 pT in the case of normal and flat-top distributions with a butterfly index BI = 1 but reaches \~ 35\textendash95 pT in the case of distinct butterfly distributions with BI > 1.3. For magnetosonic waves with amplitudes >50 pT, the occurrence rate of butterfly distribution is above 80\%. Our study suggests that energetic electron butterfly distributions in the slot region are primarily caused by magnetosonic waves. Yang, Chang; Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Wang, Shui; Spence, H.; Reeves, G.; Baker, D.; Blake, J.; Funsten, H.; Published by: Geophysical Research Letters Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2017GL073116 butterfly distributions; Electron acceleration; Landau resonance; magnetosonic wave; Radiation belt; Van Allen Probes; Wave-particle interaction |
| 2016 |
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Explaining occurrences of auroral kilometric radiation in Van Allen radiation belts Auroral kilometric radiation (AKR) is a strong terrestrial radio emission and dominates at higher latitudes because of reflection in vicinities of the source cavity and plasmapause. Recently, Van Allen Probes have observed occurrences of AKR emission in the equatorial region of Earth\textquoterights radiation belts but its origin still remains an open question. Equatorial AKR can produce efficient acceleration of radiation belt electrons and is a risk to space weather. Here we report high-resolution observations during two small storm periods 4\textendash6 April and 18\textendash20 May 2013 and show, using a 3-D ray tracing simulation, that AKR can propagate downward all the way into the equatorial plane in the radiation belts under appropriate conditions. The simulated results can successfully explain the observed AKR\textquoterights spatial distribution and frequency range, and the current results have a wide application to all other magnetized astrophysical objects in the universe. Xiao, Fuliang; Zhou, Qinghua; Su, Zhenpeng; He, Zhaoguo; Yang, Chang; Liu, Si; He, Yihua; Gao, Zhonglei; Published by: Geophysical Research Letters Published on: 12/2016 YEAR: 2016 DOI: 10.1002/2016GL071728 AKR emissions; Geomagnetic storms; Radiation belts; ray tracing simulations; satellite data; Van Allen Probes |
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Evolution of chorus emissions into plasmaspheric hiss observed by Van Allen Probes The two classes of whistler mode waves (chorus and hiss) play different roles in the dynamics of radiation belt energetic electrons. Chorus can efficiently accelerate energetic electrons, and hiss is responsible for the loss of energetic electrons. Previous studies have proposed that chorus is the source of plasmaspheric hiss, but this still requires an observational confirmation because the previously observed chorus and hiss emissions were not in the same frequency range in the same time. Here we report simultaneous observations form Van Allen Probes that chorus and hiss emissions occurred in the same range \~300\textendash1500 Hz with the peak wave power density about 10-5 nT2/Hz during a weak storm on 3 July 2014. Chorus emissions propagate in a broad region outside the plasmapause. Meanwhile, hiss emissions are confined inside the plasmasphere, with a higher intensity and a broader area at a lower frequency. A sum of bi-Maxwellian distribution is used to model the observed anisotropic electron distributions and to evaluate the instability of waves. A three-dimensional ray tracing simulation shows that a portion of chorus emission outside the plasmasphere can propagate into the plasmasphere and evolve into plasmaspheric hiss. Moreover, hiss waves below 1 kHz are more intense and propagate over a broader area than those above 1 kHz, consistent with the observation. The current results can explain distributions of the observed hiss emission and provide a further support for the mechanism of evolution of chorus into hiss emissions. Zhou, Qinghua; Xiao, Fuliang; Yang, Chang; Liu, Si; He, Yihua; Wygant, J.; Baker, D.; Spence, H.; Reeves, G.; Funsten, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2016 YEAR: 2016 DOI: 10.1002/2016JA022366 chorus waves; Plasmaspheric Hiss; RBSP results; Van Allen Probes |
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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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Ultra-low-frequency wave-driven diffusion of radiation belt relativistic electrons Van Allen radiation belts are typically two zones of energetic particles encircling the Earth separated by the slot region. How the outer radiation belt electrons are accelerated to relativistic energies remains an unanswered question. Recent studies have presented compelling evidence for the local acceleration by very-low-frequency (VLF) chorus waves. However, there has been a competing theory to the local acceleration, radial diffusion by ultra-low-frequency (ULF) waves, whose importance has not yet been determined definitively. Here we report a unique radiation belt event with intense ULF waves but no detectable VLF chorus waves. Our results demonstrate that the ULF waves moved the inner edge of the outer radiation belt earthward 0.3 Earth radii and enhanced the relativistic electron fluxes by up to one order of magnitude near the slot region within about 10 h, providing strong evidence for the radial diffusion of radiation belt relativistic electrons. Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zong, Q.-G.; Zhou, X.-Z.; Zheng, Huinan; Wang, Yuming; Wang, Shui; Hao, Y.-X.; Gao, Zhonglei; He, Zhaoguo; Baker, D.; Spence, H.; Reeves, G.; Blake, J.; Wygant, J.; Published by: Nature Communications Published on: 12/2015 YEAR: 2015 DOI: 10.1038/ncomms10096 |
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Penetration of magnetosonic waves into the plasmasphere observed by the Van Allen Probes During the small storm on 14\textendash15 April 2014, Van Allen Probe A measured a continuously distinct proton ring distribution and enhanced magnetosonic (MS) waves along its orbit outside the plasmapause. Inside the plasmasphere, strong MS waves were still present but the distinct proton ring distribution was falling steeply with distance. We adopt a sum of subtracted bi-Maxwellian components to model the observed proton ring distribution and simulate the wave trajectory and growth. MS waves at first propagate toward lower L shells outside the plasmasphere, with rapidly increasing path gains related to the continuous proton ring distribution. The waves then gradually cross the plasmapause into the deep plasmasphere, with almost unchanged path gains due to the falling proton ring distribution and higher ambient density. These results present the first report on how MS waves penetrate into the plasmasphere with the aid of the continuous proton ring distributions during weak geomagnetic activities. Xiao, Fuliang; Zhou, Qinghua; He, Yihua; Yang, Chang; Liu, Si; Baker, D.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Published by: Geophysical Research Letters Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015GL065745 Geomagnetic storms; magnetosonic waves; proton ring distribution; Radiation belts; Van Allen Probe results; Van Allen Probes; Wave-particle interaction |
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We report correlated data on nightside chorus waves and energetic electrons during two small storm periods: 1 November 2012 (Dst≈-45) and 14 January 2013 (Dst≈-18). The Van Allen Probes simultaneously observed strong chorus waves at locations L = 5.8 - 6.3, with a lower frequency band 0.1 - 0.5fce and a peak spectral density \~[10-4 nT2/Hz. In the same period, the fluxes and anisotropy of energetic (\~ 10-300 keV) electrons were greatly enhanced in the interval of large negative interplanetary magnetic field Bz. Using a bi-Maxwellian distribution to model the observed electron distribution, we perform ray tracing simulations to show that nightside chorus waves are indeed produced by the observed electron distribution with a peak growth for a field-aligned propagation around between 0.3fce and 0.4fce, at latitude <7o. Moreover, chorus waves launched with initial normal angles either θ < 90o or >90o propagate along the field either northward or southward, and then bounce back either away from Earth for a lower frequency or towards Earth for higher frequencies. The current results indicate that nightside chorus waves can be excited even during weak geomagnetic activities in cases of continuous injection associated with negative Bz. Moreover, we examine a dayside event during a small storm C on 8 May 2014 (Dst≈-45) and find that the observed anisotropic energetic electron distributions potentially contribute to the generation of dayside chorus waves, but this requires more thorough studies in the future. He, Yihua; Xiao, Fuliang; Zhou, Qinghua; Yang, Chang; Liu, Si; Baker, D.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015JA021376 chorus wave excitation; energetic electrons; Geomagnetic storm; Van Allen Probes; Van Allen probes results; Wave-particle interaction |
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Wave-driven butterfly distribution of Van Allen belt relativistic electrons Van Allen radiation belts consist of relativistic electrons trapped by Earth\textquoterights magnetic field. Trapped electrons often drift azimuthally around Earth and display a butterfly pitch angle distribution of a minimum at 90\textdegree further out than geostationary orbit. This is usually attributed to drift shell splitting resulting from day\textendashnight asymmetry in Earth\textquoterights magnetic field. However, direct observation of a butterfly distribution well inside of geostationary orbit and the origin of this phenomenon have not been provided so far. Here we report high-resolution observation that a unusual butterfly pitch angle distribution of relativistic electrons occurred within 5 Earth radii during the 28 June 2013 geomagnetic storm. Simulation results show that combined acceleration by chorus and magnetosonic waves can successfully explain the electron flux evolution both in the energy and butterfly pitch angle distribution. The current provides a great support for the mechanism of wave-driven butterfly distribution of relativistic electrons. Xiao, Fuliang; Yang, Chang; Su, Zhenpeng; Zhou, Qinghua; He, Zhaoguo; He, Yihua; Baker, D.; Spence, H.; Funsten, H.; Blake, J.; Published by: Nature Communications Published on: 05/2015 YEAR: 2015 DOI: 10.1038/ncomms9590 |
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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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During 18 February to 2 March 2014, the Van Allen Probes encountered multiple geomagnetic storms and simultaneously observed intensified chorus and hiss waves. During this period, there were substantial enhancements in fluxes of energetic (53.8 - 108.3 keV) and relativistic (2 - 3.6 MeV) electrons. Chorus waves were excited at locations L = 4 - 6.2 after the fluxes of energetic were greatly enhanced, with a lower frequency band and wave amplitudes \~ 20 - 100 pT. Strong hiss waves occurred primarily in the main phases or below the location L = 4 in the recovery phases. Relativistic electron fluxes decreased in the main phases due to the adiabatic (e.g., the magnetopause shadowing) or non-adiabatic (hiss-induced scattering) processes. In the recovery phases, relativistic electron fluxes either increased in the presence of enhanced chorus, or remained unchanged in the absence of strong chorus or hiss. The observed relativistic electron phase space density peaked around L* = 4.5, characteristic of local acceleration. This multiple-storm period reveals a typical picture that chorus waves are excited by the energetic electrons at first and then produce efficient acceleration of relativistic electrons. This further demonstrates that the interplay between both competing mechanisms of chorus-driven acceleration and hiss-driven scattering often occurs in the outer radiation belts. Liu, Si; Xiao, Fuliang; Yang, Chang; He, Yihua; Zhou, Qinghua; 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: 01/2015 YEAR: 2015 DOI: 10.1002/2014JA020781 |
| 2014 |
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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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Excitation of nightside magnetosonic waves observed by Van Allen Probes During the recovery phase of the geomagnetic storm on 30-31 March 2013, Van Allen Probe A detected enhanced magnetosonic (MS) waves in a broad range of L =1.8-4.7 and MLT =17-22 h, with a frequency range ~10-100 Hz. In the meanwhile, distinct proton ring distributions with peaks at energies of ~10 keV, were also observed in L =3.2-4.6 and L =5.0-5.6. Using a subtracted bi-Maxwellian distribution to model the observed proton ring distribution, we perform three dimensional ray tracing to investigate the instability, propagation and spatial distribution of MS waves. Numerical results show that nightside MS waves are produced by proton ring distribution and grow rapidly from the source location L =5.6 to the location L =5.0, but remain nearly stable at locations L <5.0 Moreover, waves launched toward lower L-shells with different initial azimuthal angles propagate across different MLT regions with divergent paths at first, then gradually turn back toward higher L-shells and propagate across different MLT regions with convergent paths. The current results further reveal that MS waves are generated by a ring distribution of ~10 keV proton and proton ring in one region can contribute to the MS wave power in another region. Zhou, Qinghua; Xiao, Fuliang; Yang, Chang; Liu, Si; 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: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020481 magnetosonic wave; RBSP results; Van Allen Probes; Wave-particle interaction |
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Chorus-driven acceleration of radiation belt electrons in the unusual temporal/spatial regions Cyclotron resonance with whistler-mode chorus waves is an important mechanism for the local acceleration of radiation belt energetic electrons. Such acceleration process has been widely investigated during the storm times, and its favored region is usually considered to be the low-density plasmatrough with magnetic local time (MLT) from midnight through dawn to noon. Here we present two case studies on the chorus-driven acceleration of radiation belt electrons in some \textquotedblleftunusual\textquotedblright temporal /spatial regions. (1) The first event recorded by the Van Allen Probes during the nonstorm times from 21 to 23 February 2013. Within two days, a new radiation belt centering around L=5.8 formed and gradually merged with the original outer belt. The corresponding relativistic electron fluxes increased by a factor of up to 50, accompanied by strong chorus waves. The quasi-linear STEERB model, including the local acceleration of detected chorus waves, can basically reproduce the observed 0.2\textendash5.0 MeV electron flux enhancement at the center of new belt. These results clearly illustrate the importance of chorus-driven local acceleration during the nonstorm times. (2) The second event observed by the Van Allen Probes in the duskside (MLT\~18) region on 2 October 2013. The quasi-linear diffusion analysis of STEERB code shows that, even in the duskside region with large ratio between the electron plasma frequency and the electron gyrofrequency, the detected intense (\~0.5 nT) chorus waves can still effectively accelerate radiation belt electrons. These results clearly exhibit the broader effective acceleration regions than usually estimated, at least for this one example. Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; Zhu, Hui; Published by: Published on: 08/2014 YEAR: 2014 DOI: 10.1109/URSIGASS.2014.6929875 |
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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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Chorus acceleration of radiation belt relativistic electrons during March 2013 geomagnetic storm The recent launching of Van Allen probes provides an unprecedent opportunity to investigate variations of the radiation belt relativistic electrons. During the 17\textendash19 March 2013 storm, the Van Allen probes simultaneously detected strong chorus waves and substantial increases in fluxes of relativistic (2 - 4.5 MeV) electrons around L = 4.5. Chorus waves occurred within the lower band 0.1\textendash0.5fce (the electron equatorial gyrofrequency), with a peak spectral density \~10-4 nT2/Hz. Correspondingly, relativistic electron fluxes increased by a factor of 102\textendash103 during the recovery phase compared to the main phase levels. By means of a Gaussian fit to the observed chorus spectra, the drift and bounce-averaged diffusion coefficients are calculated and then used to solve a 2-D Fokker-Planck diffusion equation. Numerical simulations demonstrate that the lower-band chorus waves indeed produce such huge enhancements in relativistic electron fluxes within 15 h, fitting well with the observation. Xiao, Fuliang; Yang, Chang; He, Zhaoguo; Su, Zhenpeng; Zhou, Qinghua; He, Yihua; 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: 05/2014 YEAR: 2014 DOI: 10.1002/2014JA019822 |
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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 |
| 1998 |
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Resonant diffusion curves for electron cyclotron resonance with field-aligned electromagnetic R mode and L mode electromagnetic ion cyclotron (EMIC) waves are constructed using a fully relativistic treatment. Analytical solutions are derived for the case of a single-ion plasma, and a numerical scheme is developed for the more realistic case of a multi-ion plasma. Diffusion curves are presented, for plasma parameters representative of the Earth\textquoterights magnetosphere at locations both inside and outside the plasmapause. The results obtained indicate minimal electron energy change along the diffusion curves for resonant interaction with L mode waves. Intense storm time EMIC waves are therefore ineffective for electron stochastic acceleration, although these waves could induce rapid pitch angle scattering for ≳ 1 MeV electrons near the duskside plasmapause. In contrast, significant energy change can occur along the diffusion curves for interaction between resonant electrons and whistler (R mode) waves. The energy change is most pronounced in regions of low plasma density. This suggests that whistler mode waves could provide a viable mechanism for electron acceleration from energies near 100 keV to above 1 MeV in the region outside the plasmapause during the recovery phase of geomagnetic storms. A model is proposed to account for the observed variations in the flux and pitch angle distribution of relativistic electrons during geomagnetic storms by combining pitch angle scattering by intense EMIC waves and energy diffusion during cyclotron resonant interaction with whistler mode chorus outside the plasmasphere. Summers, D.; Thorne, Richard; Xiao, Fuliang; Published by: Journal of Geophysical Research Published on: 09/1998 YEAR: 1998 DOI: 10.1029/98JA01740 |
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