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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 3/4
Nonlin. Processes Geophys., 6, 169–178, 1999
https://doi.org/10.5194/npg-6-169-1999
© Author(s) 1999. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

Special issue: Nonlinear Waves and Chaos

Nonlin. Processes Geophys., 6, 169–178, 1999
https://doi.org/10.5194/npg-6-169-1999
© Author(s) 1999. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  31 Dec 1999

31 Dec 1999

Remarks on the parallel propagation of small-amplitude dispersive Alfvénic waves

S. Champeaux1, D. Laveder2, T. Passot2, and P. L. Sulem2 S. Champeaux et al.
  • 1Physics Department, University of California at San Diego, La Jolla, CA 92093-0319, USA
  • 2CNRS. UMR 6529, Observatoire de la Côte d'Azur, B.P. 4229, 06304 Nice cedex 4, France

Abstract. The envelope formalism for the description of a small-amplitude parallel-propagating Alfvén wave train is tested against direct numerical simulations of the Hall-MHD equations in one space dimension where kinetic effects are neglected. It turns out that the magnetosonic-wave dynamics departs from the adiabatic approximation not only near the resonance between the speed of sound and the Alfvén wave group velocity, but also when the speed of sound lies between the group and phase velocities of the Alfvén wave. The modulational instability then does not anymore affect asymptotically large scales and strong nonlinear effects can develop even in the absence of the decay instability. When the Hall-MHD equations are considered in the long-wavelength limit, the weakly nonlinear dynamics is accurately reproduced by the derivative nonlinear Schrödinger equation on the expected time scale, provided no decay instabilities are present. The stronger nonlinear regime which develops at later time is captured by including the coupling to the nonlinear dynamics of the magnetosonic waves.

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