Asymptotic and time-dependent solutions of magnetic pulsations in realistic magnetic field geometries

Details Asymptotic and time-dependent solutions of magnetic pulsations in realistic magnetic field geometries Asymptotic and time-dependent solutions of magnetic pulsations in realistic magnetic field geometries

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992jgr....97.6439w&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 97, no. A5, May 1, 1992, p. 6439-6450. Research supported by SERC.

Physics

15

Asymptotic Methods, Earth Magnetosphere, Geomagnetic Pulsations, Magnetic Field Configurations, Magnetohydrodynamic Waves, Time Dependence, Wave Excitation, Beta Factor, Cold Plasmas, Coupled Modes, Perturbation Theory, Wave Equations

Scientific paper

The coupling of compressional and Alfven modes is important in solar, magnetospheric, and laboratory plasmas. Such coupling within a general framework is investigated, with emphasis on applying the results to the excitation of Alfven waves in the magnetosphere. The Alfvenic response of an arbitrary (curl-free) magnetic field and ideal cold plasma is considered, and the Alfven wave equation is shown to be driven by perturbation magnetic pressure gradients aligned with the Alfven fields. The efficiency with which any particular standing Alfven wave is excited is governed by an overlap integral along the background field line of the Alfven mode and the perturbation magnetic pressure gradient. Three types of compressional driving function are investigated which produce diverse behavior and may excite resonant and nonresonant Alfven waves. These waves oscillate with either the natural Alfven frequency or the frequency of the driver. Finally, the attention is turned to the long-term, or asymptotic, state of the fields. A nonlinear solution is derived which is a generalization of earlier work. It is found that the standing Alfven waves will be confined to thin layers.

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