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Formation of multiple energy dispersion of H + , He + , and O + ions in the inner magnetosphere in response to interplanetary shock
Author(s) -
Tsuji H.,
Ebihara Y.,
Tanaka T.
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2016ja023704
Subject(s) - physics , magnetosphere , ion , atomic physics , dispersion (optics) , energy flux , electric field , computational physics , flux (metallurgy) , solar wind , particle acceleration , shock wave , geophysics , plasma , nuclear physics , optics , mechanics , materials science , astronomy , quantum mechanics , metallurgy
An interplanetary (IP) shock has a large impact on magnetospheric ions. Satellite observations have shown that soon after arrival of the IP shock, overall intensity of the ions rapidly increases and multiple energy dispersion appears in an energy‐time spectrogram of the ions. In order to understand the response of the magnetospheric ions to IP shock, we have performed test particle simulation under the electric and magnetic fields provided by the global magnetohydrodynamic simulation. We reconstructed the differential flux of H + , He + , and O + ions at (7, 0, 0) Re in GSM coordinates by means of the semi‐Lagrangian (phase space mapping) method. Simulation results show that the ions respond to the IP shock in two different ways. First, overall intensity of the flux gradually increases at all pitch angles. As the compressional wave propagates tailward, the magnetic field increases, which accelerates the ions due to the gyrobetatron. Second, multiple energy‐time dispersion appears in the reconstructed spectrograms of the ion flux. The energy‐time dispersion is caused by the ion moving toward mirror point together with tailward propagating compressional wave at off‐equator. The ions are primarily accelerated by the drift betatron under the strong electric field looking dawnward. The dispersion is absent in the spectrogram of equatorially mirroring ions. The dispersion appears at higher energy for heavier ions. These features are consistent with the satellite observations. Because the acceleration depends on bounce phase, the bounce‐averaged approximation is probably invalid for the ions during the interval of geomagnetic sudden commencement.