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AGU: Journal of Geophysical Research, Space Physics

 

Keywords

  • electromagnetic ion cyclotron waves
  • hybrid code
  • numerical modeling
  • dipole geometry

Index Terms

  • Magnetospheric Physics: MHD waves and instabilities
  • Magnetospheric Physics: Numerical modeling
  • Magnetospheric Physics: Plasma waves and instabilities
  • Magnetospheric Physics: Ring current
  • Space Plasma Physics: Mathematical and numerical techniques
Abstract
Cited By (0)
 

Abstract

Two-dimensional hybrid code simulation of electromagnetic ion cyclotron waves in a dipole magnetic field

Y. Hu

Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire, USA

R. E. Denton

Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire, USA

Proton temperature anisotropy (T ⊥p/T ∥p > 1) with sufficiently high β ∥p will drive the electromagnetic ion cyclotron (EMIC) instability. A two-dimensional hybrid code is employed to simulate the EMIC waves in a dipole magnetic field. We initialize the electron-proton plasma such that the MHD equilibrium J × B = −∇ · inline equation is satisfied for the parallel force, while it is only satisfied along the magnetic equator for the perpendicular force. A high temperature ratio T ⊥p/T ∥p = 9 and low plasma beta β ∥p = 0.1 are used to lessen the effects of nonequilibrium off the equator. The plasma is more unstable to the EMIC waves along the magnetic equator where the temperature ratio is high and the plasma β is low. There, waves are generated with dominant left-hand polarization with the expected EMIC wave frequencies based on linear theory. These waves propagate along the magnetic field toward the ionosphere; and the inhomogeneity of the magnetic field causes the waves in the low L shell region to travel faster than those in the high L shell, so that the wavefronts turn oblique to the local magnetic field. When the wave vector turns perpendicular to the magnetic field at high magnetic latitudes, the initially left-hand waves become linearly polarized. The linear polarization of the EMIC waves is consistent with some observations and with ray tracing results for reflected waves. We also introduce resistive layers to damp the waves near the boundaries to reduce the waves that are reflected by the boundary condition. The power spectra indicate that there is a radial propagation of wave energy with a group speed equal to about 0.1 times the equatorial Alfvén speed. Additionally, we find that there is a radial coherence length equal to about 10 c/ωpp0 associated with the EMIC wave structure.

Received 15 June 2009; accepted 28 August 2009; published 29 December 2009.

Citation: Hu, Y., and R. E. Denton (2009), Two-dimensional hybrid code simulation of electromagnetic ion cyclotron waves in a dipole magnetic field, J. Geophys. Res., 114, A12217, doi:10.1029/2009JA014570.

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