Abstract
Abstract. The eigenmodes of low frequency perturbations of thin anisotropic current sheets with a finite value of the normal magnetic field, are investigated in this paper. It is shown that two possible polarizations of symmetric and asymmetric modes (sausage and kink) exist where the growth rate of instabilities is positive. In addition, we demonstrate that a tearing instability might have a positive growth rate in thin anisotropic current sheets. The class of relatively fast wavy flapping oscillations observed by Cluster is described. The main direction of wave motion coincides with the direction of the current and the typical velocity of this motion is comparable with the plasma drift velocity in the current sheet. The comparison of these characteristics with theoretical predictions of the model of anisotropic thin current sheets, demonstrates that, in principle, the theory adequately describes the observations.
Highlights
The numerous attempts to describe current sheets (CSs) in the Earth’s magnetosphere and to investigate their stability led to the development of a variety of models of CS
Artemyev tions and/or quasi-adiabaticity of ion motion in thin current sheets, was recently developed (Zelenyi et al, 2004; Sitnov et al, 2006)
The linear stability analysis of low frequency wave modes propagating in the thin current sheet shows that unstable modes can have two different polarizations
Summary
The numerous attempts to describe current sheets (CSs) in the Earth’s magnetosphere and to investigate their stability led to the development of a variety of models of CS. Contrary to well-known isotropic models, the general theory of anisotropic thin CS (TCS) instabilities, which might be useful to compare the typical temporal and spatial characteristics of observed CSs, has not been developed yet. We present our first results devoted to the further development of the general theory of oblique instabilities (of tearing, kink, sausage and oblique eigenmodes) in anisotropic TCSs. L. Other TCS modes (e.g. kink and sausage), which propagate perpendicularly to the magnetic field, might develop in anisotropic CSs with Bz=0. The values of their growth rates are comparable. The first order of the perturbation of velocity distribution function f1j might be found on the base of the linearized Vlasov equation:
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