Field-line Resonances in a Time-varying Magnetosphere

다국어 초록 (Multilingual Abstract)

Field line resonances, which represent shear Alfven standing modes of magnetohydrodynamic(MHD) waves are studied in space for the case in which magnetosphere is being perturbed in timeby solarwind variations. A linearizedMHD wave model has been developed with time-varying Alfvenspeeds. When the magnetosphere becomes quiet, field line resonances consistently occur over manyharmonics. A time-varying Alfven speed is found to cause a significant broadening of each spectralpeak, which strongly depends on the frequency. While fundamental mode or lower harmonicsbecome relatively stable with less broadening, higher harmonics appear with strong dispersion.
Our results are consistent with the observed feature that fundamental or lower harmonic modesare dominant and higher harmonics are less frequently excited in space where the system is oftenperturbed in time.

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