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Ann. Geophys., 24, 1077-1084, 2006
www.ann-geophys.net/24/1077/2006/
© European Geosciences Union 2006
Axisymmetric Alfvén resonances in a multi-component plasma at finite ion gyrofrequency
D. Yu. Klimushkin1, P. N. Mager1, and K.-H. Glassmeier2
1Institute of Solar-Terrestrial Physics (ISTP), Russian Academy of Science, Siberian Branch, Irkutsk, P.O.Box 4026, 664033, Russia
2Institut für Geophysik und Extraterrestrische Physik, Mendelssohnstr. 3, D-38106 Braunschweig, Germany
Abstract. This paper deals with the spatial structure of zero azimuthal wave number ULF oscillations in a
1-D inhomogeneous multi-component plasma when a finite ion gyrofrequency is taken into account. Such oscillations may
occur in the terrestrial magnetosphere as Pc1-3 waves or in the magnetosphere of the planet Mercury. The wave field
was found to have a sharp peak on some magnetic surfaces, an analogy of the Alfvén (field line) resonance in
one-fluid MHD theory. The resonance can only take place for waves with frequencies in the intervals
ω<ωch or Ω0<ω< ωcp, where ωch and ωcp are heavy and light ions
gyrofrequencies, and Ω0 is a kind of hybrid frequency. Contrary to ordinary Alfvén resonance, the wave
resonance under consideration takes place even at the zero azimuthal wave number. The radial component of the wave
electric field has a pole-type singularity, while the azimuthal component is finite but has a branching point
singularity on the resonance surface. The later singularity can disappear at some frequencies. In the region
adjacent to the resonant surface the mode is standing across the magnetic shells.
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