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2018
Authors: Min Kyungguk, Boardsen Scott A., Denton Richard E, and Liu Kaijun
Title: Equatorial Evolution of the Fast Magnetosonic Mode in the Source Region: Observation-Simulation Comparison of the Preferential Propagation Direction
Abstract: Recent analysis of an event observed by the Van Allen Probes in the source region outside the plasmapause has shown that fast magnetosonic waves (also referred to as equatorial noise) propagate preferentially in the azimuthal direction, implying that wave amplification should occur during azimuthal propagation. To demonstrate this, we carry out 2‐D particle‐in‐cell simulations of the fast magnetosonic mode at the dipole magnetic equator with the simulation box size, the magnetic field inhomogeneity, and the plasma parameters chosen from the same event recently analyzed. The self‐consistently evolving electric and magnetic field fluctuations are characterized by spectral peaks at harmonics of the local proton cyclotron frequency. The azimuthal component of the electric field fluctua. . .
Date: 11/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA026037 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA026037
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Authors: Min Kyungguk, Liu Kaijun, Wang Xueyi, Chen Lunjin, and Denton Richard E
Title: Fast Magnetosonic Waves Observed by Van Allen Probes: Testing Local Wave Excitation Mechanism
Abstract: Linear Vlasov theory and particle-in-cell (PIC) simulations for electromagnetic fluctuations in a homogeneous, magnetized, and collisionless plasma are used to investigate a fast magnetosonic wave event observed by the Van Allen Probes. The fluctuating magnetic field observed exhibits a series of spectral peaks at harmonics of the proton cyclotron frequency Ωp and has a dominant compressional component, which can be classified as fast magnetosonic waves. Furthermore, the simultaneously observed proton phase space density exhibits positive slopes in the perpendicular velocity space, ∂fp/∂v⊥>0, which can be a source for these waves. Linear theory analyses and PIC simulations use plasma and field parameters measured in situ except that the modeled proton distribution is modified to hav. . .
Date: 01/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024867 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024867/full
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2017
Authors: Min Kyungguk, Denton Richard E, Liu Kaijun, Gary Peter, and Spence Harlan E.
Title: Ion Bernstein instability as a possible source for oxygen ion cyclotron harmonic waves
Abstract: This paper demonstrates that an ion Bernstein instability can be a possible source for recently reported electromagnetic waves with frequencies at or near the singly ionized oxygen ion cyclotron frequency, inline image, and its harmonics. The particle measurements during strong wave activity revealed a relatively high concentration of oxygen ions (∼15%) whose phase space density exhibits a local peak at energy ∼20 keV. Given that the electron plasma-to-cyclotron frequency ratio is inline image, this energy corresponds to the particle speed inline image, where vA is the oxygen Alfvén speed. Using the observational key plasma parameters, a simplified ion velocity distribution is constructed, where the local peak in the oxygen ion velocity distribution is represented by an isotropic s. . .
Date: 05/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA023979 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA023979/full
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2015
Authors: Min Kyungguk, Liu Kaijun, Bonnell John W., Breneman Aaron W., Denton Richard E, et al.
Title: Study of EMIC wave excitation using direct ion measurements
Abstract: With data from Van Allen Probes, we investigate EMIC wave excitation using simultaneously observed ion distributions. Strong He-band waves occurred while the spacecraft was moving through an enhanced density region. We extract from Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer measurement the velocity distributions of warm heavy ions as well as anisotropic energetic protons that drive wave growth through the ion cyclotron instability. Fitting the measured ion fluxes to multiple sinm-type distribution functions, we find that the observed ions make up about 15% of the total ions, but about 85% of them are still missing. By making legitimate estimates of the unseen cold (below ~2 eV) ion composition from cutoff frequencies suggested by the observed wave spectrum, a series of. . .
Date: 03/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020717 Available at: http://doi.wiley.com/10.1002/2014JA020717
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2014
Authors: Fu Xiangrong, Cowee Misa M., Friedel Reinhard H., Funsten Herbert O, Gary Peter, et al.
Title: Whistler Anisotropy Instabilities as the Source of Banded Chorus: Van Allen Probes Observations and Particle-in-Cell Simulations
Abstract: Magnetospheric banded chorus is enhanced whistler waves with frequencies ωr < Ωe, where Ωe is the electron cyclotron frequency, and a characteristic spectral gap at ωr ≃ Ωe/2. This paper uses spacecraft observations and two-dimensional particle-in-cell (PIC) simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from HOPE instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron mod. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020364 Available at: http://doi.wiley.com/10.1002/2014JA020364
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