Biblio

Found 7 results
Filters: Keyword is Ring current ions  [Clear All Filters]
2019
Authors: Yuan Zhigang, Yu Xiongdong, Ouyang Zhihai, Yao Fei, Huang Shiyong, et al.
Title: Simultaneous trapping of EMIC and MS waves by background plasmas
Abstract: Electromagnetic ion cyclotron waves and fast magnetosonic waves are found to be simultaneously modulated by background plasma density: both kinds of waves were observed in high plasma density regions but vanished in low density regions. Theoretical analysis based on Snell's law and linear growth theory have been utilized to investigate the physical mechanisms driving such modulation. It is suggested that the modulation of fast magnetosonic waves might be due to trapping by plasma density structures, which results from a conservation of the parameter Q during their propagation. Here Q = nrsinψ, with n the refractive index, r the radial distance, and ψ the wave azimuthal angle. As for electromagnetic ion cyclotron waves, the modulation might be owed to the ion composition difference betwee. . .
Date: 02/2019 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA026149 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA026149
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2018
Authors: Yuan Zhigang, Yu Xiongdong, Huang Shiyong, Qiao Zheng, Yao Fei, et al.
Title: Cold Ion Heating by Magnetosonic Waves in a Density Cavity of the Plasmasphere
Abstract: Fast magnetosonic (MS) waves play an important role in the dynamics of the inner magnetosphere. Theoretical prediction and simulation have demonstrated that MS waves can heat cold ions. However, direct observational evidence of cold ion heating by MS waves has so far remained elusive. In this paper, we show a typical event of cold ion heating by magnetosonic waves in a density cavity of the plasmasphere with observations of the Van Allen Probe mission on 22 August 2013. During enhancements of the MS wave intensity in the density cavity, the fluxes of trapped H+ and He+ ions with energies of 10–100 eV were observed to increase, implying that cold plasmaspheric ions were heated through high-order resonances with the MS waves. Based on simultaneous observations of ring current protons, we h. . .
Date: 02/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024919 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024919/full
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2017
Authors: Yuan Zhigang, Yu Xiongdong, Huang Shiyong, Wang Dedong, and Funsten Herbert O.
Title: In situ observations of magnetosonic waves modulated by background plasma density
Abstract: We report in situ observations by the Van Allen Probe mission that magnetosonic (MS) waves are clearly relevant to appear relevant to the background plasma number density. As the satellite moved across dense and tenuous plasma alternatively, MS waves occurred only in lower density region. As the observed protons with ‘ring’ distributions provide free energy, local linear growth rates are calculated and show that magnetosonic waves can be locally excited in tenuous plasma. With variations of the background plasma density, the temporal variations of local wave growth rates calculated with the observed proton ring distributions, show a remarkable agreement with those of the observed wave amplitude. Therefore, the paper provides a direct proof that background plasma densities can modulate . . .
Date: 07/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074681 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL074681/full
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Authors: He Zhaoguo, Chen Lunjin, Zhu Hui, Xia Zhiyang, Reeves G D, et al.
Title: Multiple-satellite observation of magnetic dip event during the substorm on 10 October, 2013
Abstract: We present a multiple-satellite observation of the magnetic dip event during the substorm on October 10, 2013. The observation illustrates the temporal and spatial evolution of the magnetic dip and gives a compelling evidence that ring current ions induce the magnetic dip by enhanced plasma beta. The dip moves with the energetic ions in a comparable drift velocity and affects the dynamics of relativistic electrons in the radiation belt. In addition, the magnetic dip provides a favorable condition for the EMIC wave generation based on the linear theory analysis. The calculated proton diffusion coefficients show that the observed EMIC wave can lead to the pitch angle scattering losses of the ring current ions, which in turn partially relax the magnetic dip in the observations. This study enr. . .
Date: 09/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074869 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL074869/full
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Authors: Xiongdong Yu, Zhigang Yuan, Dedong Wang, Shiyong Huang, Haimeng Li, et al.
Title: Oxygen cyclotron harmonic waves observed by the Van Allen Probes
Abstract: Fine structured multiple-harmonic electromagnetic emissions at frequencies around the equatorial oxygen cyclotron harmonics are observed by Van Allen Probe A outside the core plasmasphere (L~5) off the magnetic equator (MLAT~-7.5°) during a magnetic storm. We find that the multiple-harmonic emissions have their PSD peaks at 2~8 equatorial oxygen gyro-harmonics (f~nfO+, n=2~8) while the fundamental mode (n=1) is absent, implying that the harmonic waves are generated near the equator and propagate into the observation region. Additionally these electromagnetic emissions are linear polarized. Different from the equatorial noise emission propagating very obliquely, these emissions have moderate wave normal angles (about 40°~60°) which predominately become larger as the harmonic number incre. . .
Date: 03/2017 Publisher: Science China: Earth Sciences DOI: 10.1007/s11430-016-9024-3 Available at: http://engine.scichina.com/publisher/scp/journal/SCES/doi/10.1007/s11430-016-9024-3
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2016
Authors: Yuan Zhigang, Yu Xiongdong, Wang Dedong, Huang Shiyong, Li Haimeng, et al.
Title: In situ evidence of the modification of the parallel propagation of EMIC waves by heated He + ions
Abstract: With observations of the Van Allen Probe B, we report in situ evidence of the modification of the parallel propagating electromagnetic ion cyclotron (EMIC) waves by heated He+ ions. In the outer boundary of the plasmasphere, accompanied with the He+ ion heating, the frequency bands of H+ and He+ for EMIC waves merged into each other, leading to the disappearance of a usual stop band between the gyrofrequency of He+ ions (ΩHe+) and the H+ cutoff frequency (ωH+co) in the cold plasma. Moreover, the dispersion relation for EMIC waves theoretically calculated with the observed plasma parameters also demonstrates that EMIC waves can indeed parallel propagate across ΩHe+. Therefore, the paper provides an in situ evidence of the modification of the parallel propagation of EMIC waves by heated H. . .
Date: 07/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022573 Available at: http://doi.wiley.com/10.1002/2016JA022573
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2015
Authors: Zhao H., Li X, Baker D N, Fennell J. F., Blake J B, et al.
Title: The evolution of ring current ion energy density and energy content during geomagnetic storms based on Van Allen Probes measurements
Abstract: Enabled by the comprehensive measurements from the MagEIS, HOPE, and RBSPICE instruments onboard Van Allen Probes in the heart of the radiation belt, the relative contributions of ions with different energies and species to the ring current energy density and their dependence on the phases of geomagnetic storms are quantified. The results show that lower energy (<50 keV) protons enhance much more often and also decay much faster than higher energy protons. During the storm main phase, ions with energies < 50 keV contribute more significantly to the ring current than those with higher energies; while the higher energy protons dominate during the recovery phase and quiet times. The enhancements of higher energy proton fluxes as well as energy content generally occur later than those of lower. . .
Date: 08/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021533 Available at: http://doi.wiley.com/10.1002/2015JA021533
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