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Ann. Geophys., 24, 589-601, 2006
www.ann-geophys.net/24/589/2006/
© European Geosciences Union 2006
Dispersion equations for field-aligned cyclotron waves in axisymmetric magnetospheric plasmas
N. I. Grishanov1, M. A. Raupp1, A. F. D. Loula1, and J. Pereira Neto2
1Laboratório Nacional de Computação Científica, Av. Getulio Vargas, 333, Quitandinha, 25651-075, Petrópolis, RJ, Brasil
2Universidade do Estado do Rio de Janeiro, UERJ, Av. São F. Xavier, 538, Maracana, 20550-013, Rio de Janeiro, RJ, Brasil
Abstract. In this paper, we derive the dispersion equations for field-aligned
cyclotron waves in two-dimensional (2-D) magnetospheric plasmas with
anisotropic temperature. Two magnetic field
configurations are considered with dipole and circular magnetic field lines. The main
contribution of the trapped particles to the transverse dielectric
permittivity is estimated by solving the linearized Vlasov equation for
their perturbed distribution functions, accounting for the cyclotron and
bounce resonances, neglecting the drift effects, and assuming the weak
connection of the left-hand and right-hand polarized waves. Both the
bi-Maxwellian and bi-Lorentzian distribution functions are considered to
model the ring current ions and electrons in the dipole magnetosphere.
A numerical code has been developed to analyze the dispersion characteristics
of electromagnetic ion-cyclotron waves in an electron-proton magnetospheric
plasma with circular magnetic field lines, assuming that the steady-state
distribution function of the energetic protons is bi-Maxwellian. As in the
uniform magnetic field case, the growth rate of the proton-cyclotron
instability (PCI) in the 2-D magnetospheric plasmas is defined by the
contribution of the energetic ions/protons to the imaginary part of the
transverse permittivity elements. We demonstrate that the PCI growth rate in
the 2-D axisymmetric plasmasphere can be significantly smaller than that for
the straight magnetic field case with the same macroscopic bulk parameters.
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