MHD aspect of current sheet oscillations related to magnetic field gradients
- 1Institute for Computational Modelling, Russian Academy of Sciences, Krasnoyarsk, 660036, Russia
- 2Siberian Federal University, Krasnoyarsk, 660041, Russia
- 3St.Petersburg State University, 198504, Russia
- 4Space Research Institute, Austrian Academy of Sciences, Graz, Austria
- 5Institute for Theoretical Physics, University of Graz, Austria
- 6Institute for Geophysics, Astrophysics, and Meteorology, University of Graz, Austria
Abstract. One-fluid ideal MHD model is applied for description of current sheet flapping disturbances appearing due to a gradient of the normal magnetic field component. The wave modes are studied which are associated to the flapping waves observed in the Earth's magnetotail current sheet. In a linear approximation, solutions are obtained for model profiles of the electric current and plasma densities across the current sheet, which are described by hyperbolic functions. The flapping eigenfrequency is found as a function of wave number. For the Earth's magnetotail conditions, the estimated wave group speed is of the order of a few tens kilometers per second. The current sheet can be stable or unstable in dependence on the direction of the gradient of the normal magnetic field component. The obtained dispersion function is used for calculation of the flapping wave disturbances, which are produced by the given initial Gaussian perturbation at the center of the current sheet and propagating towards the flanks. The propagating flapping pulse has a smooth leading front, and a small scale oscillating trailing front, because the short wave oscillations propagate much slower than the long wave ones.