Calculations of dynamo coefficients in Parker unstable disks without shear

Astronomical Observatory, Jagiellonian University, 30-244 Kraków, Poland

Corresponding author: otmian@oa.uj.edu.pl

Received: 10 March 2003
Accepted: 16 May 2003

Abstract

We investigate the influence of the Coriolis force and magnetic reconnection on the evolution of the Parker instability in galactic disks. We apply a three-dimensional (3D) model of a local gas cube, permeated by an azimuthal regular magnetic field. We numerically solve MHD equations including the contribution of the Coriolis force. At this stage of the investigation we omit the effects of rotational shear. Our previous simulations demonstrate that Parker instability leads to the formation of helically twisted magnetic flux tubes forming a significant poloidal magnetic field component on the scale of the whole cube. Such an evolution represents an example of the fast dynamo process proposed by Parker (1992). In the present work we extend our earlier computations by calculating the basic coefficients of the MHD dynamo as time-dependent functions. The well-known dynamo coefficients α and – both in the relevant tensorial formulations – are derived from small scale gas motions present in the Parker instability model, so in a local formulation the total turbulent electromotive force (EMF) is described as a quantity dependent on time. The EMF-coefficients α and are evaluated within the limit of high microscopic conductivity.