EDP Sciences
Free access
Volume 408, Number 3, September IV 2003
Page(s) 817 - 828
Section Cosmology
DOI http://dx.doi.org/10.1051/0004-6361:20031032

A&A 408, 817-828 (2003)
DOI: 10.1051/0004-6361:20031032

Calculations of dynamo coefficients in Parker unstable disks without shear

K. Otmianowska-Mazur

Astronomical Observatory, Jagiellonian University, 30-244 Kraków, Poland
(Received 10 March 2003 / Accepted 16 May 2003 )

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 $\alpha$ and $\eta_{\rm T}$ - 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 $\alpha$ and $\eta_{\rm T}$ are evaluated within the limit of high microscopic conductivity.

Key words: galaxies: ISM -- galaxies: magnetic fields -- ISM: magnetic fields -- MHD

© ESO 2003