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Two-dimensional particle-in-cell simulations of magnetosonic waves in the dipole magnetic field: On a constant L-shell
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  • Kyungguk Min,
  • Kaijun Liu,
  • Richard E. Denton,
  • Frantisek Nemec,
  • Scott A. Boardsen,
  • Yoshizumi Miyoshi
Kyungguk Min
Chungnam National University, Chungnam National University

Corresponding Author:kyungguk@me.com

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Kaijun Liu
Southern University of Science and Technology, Southern University of Science and Technology
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Richard E. Denton
Dartmouth College, Dartmouth College
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Frantisek Nemec
Charles University, Charles University
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Scott A. Boardsen
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Yoshizumi Miyoshi
Institute for Space-Earth Environmental Research, Nagoya University, Institute for Space-Earth Environmental Research, Nagoya University
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Two-dimensional particle-in-cell (PIC) simulations are carried out on a constant L-shell (or drift shell) surface of the dipole magnetic field to investigate the generation process of near-equatorial fast magnetosonic waves (a.k.a equatorial noise; MSWs hereafter) in the inner magnetosphere. Unlike the simulation domain in a meridional plane used in a recent study, the present simulation box allows wave propagation and growth in the azimuthal direction, to which MSWs were shown to propagate and grow in the source region. Furthermore, the equatorial ring-like proton distribution used to drive MSWs in the present study is (realistically) weakly anisotropic. Consequently, the ring-like velocity distribution projected along the field line by Liouville’s theorem extends to rather high latitude, and linear instability analysis using the local plasma conditions predicts substantial MSW growth up to ±27° latitude. In the PIC simulations, however, the MSW intensity maximizes near the equator and decreases quasi-exponentially with latitude. Further analysis reveals that the stronger equatorward refraction at higher latitude due to the larger gradient of the dipole magnetic field strength prevents off-equatorial MSWs from growing continuously, whereas MSWs of equatorial origin experience little refraction and can fully grow. Furthermore, the simulated MSWs exhibit a rather complex wave field structure varying with latitude, and the scattering of energetic ring-like protons in response to MSW excitation occurs faster than the bounce period of those protons so that they do not necessarily follow Liouville’s theorem during MSW excitation.
Oct 2020Published in Journal of Geophysical Research: Space Physics volume 125 issue 10. 10.1029/2020JA028414