Galactic magnetic field reversals and vorticity of transition layers

E. A. Mikhailov

Faculty of Physics, Lomonosov Moscow State University, Leninskiye Gori, bldg. 1, str.~2, GSP-1, Moscow 119991, Russia

Abstract
We have studied the reversals of the magnetic field in spiral galaxies. The magnetic fields are described by dynamo theory. It is based on the joint action of alpha-effect and differential rotation. To solve the problem, equations were derived using the no-z approximation. It takes into account that the galaxy disc is quite thin, so some of the partial derivatives can be replaced by algebraic expressions. There is a small parameter that is proportional to the half-thickness of the galaxy. This gives an opportunity to use the asymptotic theory of contrast structures. The main problem is that we have a system of two equations which has three stationary solutions. Two of them are stable and the third one is non-stable. There is a transition layer between them that moves with some small velocity proportional to the squared small parameter. This layer can be associated with the field reversal. For small perturbations near the stationary solutions, the equations can be linearized and some theoretical estimates can be made. The evolution of the transition layers has been also described numerically. The results of the theoretical estimates and numerical modelling are quite similar. Tables 1, Figs 2, Refs 11.