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Ann. Geophys., 24, 2429-2433, 2006
www.ann-geophys.net/24/2429/2006/
© European Geosciences Union 2006
On impulse excitation of the global poloidal modes in the magnetosphere
P. N. Mager and D. Yu. Klimushkin
Institute of Solar-Terrestrial Physics (ISTP), Russian Academy of Science, Siberian Branch, Irkutsk, 664033, Russia
Abstract. Through the combined action of the field line curvature and finite plasma pressure in some
regions of the magnetosphere (plasmapause, ring current) there can exist global poloidal Alfvén
modes standing both along field lines and across magnetic shells and propagating along azimuth.
In this paper we investigate the spatio-temporal structure of such waves generated by an
impulsive source. In general, the mode is the sum of radial harmonics whose structure is described
by Hermitian polynomials. For the usually observed second harmonic structure along the background
field, frequencies of these radial harmonics are very close to each other; therefore, the
generated wave is almost a monochromatic oscillation. But mixing of the harmonics with different
radial structure causes the evolution of the initially poloidal wave into the toroidal one. This
casts some doubts upon the interpretation of observed high-m poloidal waves as global poloidal
modes.
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