Large scale instabilities in two-dimensional magnetohydrodynamics
Abstract
The stability of a sheared magnetic field is analyzed in two-dimensional magnetohydrodynamics with resistive and viscous dissipation. Using a multiple-scale analysis, it is shown that at large enough Reynolds numbers the basic state describing a motionless fluid and a layered magnetic field, becomes unstable with respect to large scale perturbations. The exact expressions for eddy-viscosity and eddy-resistivity are derived in the nearby of the critical point where the instability sets in. In this marginally unstable case the nonlinear phase of perturbation growth obeys to a Cahn-Hilliard-like dynamics characterized by coalescence of magnetic islands leading to a final new equilibrium state. High resolution numerical simulations confirm quantitatively the predictions of multiscale analysis.
Cite
@article{arxiv.chao-dyn/9810026,
title = {Large scale instabilities in two-dimensional magnetohydrodynamics},
author = {G. Boffetta and A. Celani and R. Prandi},
journal= {arXiv preprint arXiv:chao-dyn/9810026},
year = {2007}
}
Comments
6 pages RevTeX, 6 PostScript figures