1994A&A...286...72S

The mean-field dynamo equation is solved with a 2D timestepping code for a given flow system with the aim to investigate the equatorial symmetry of the induced magnetic fields. The turbulence pattern is assumed to be uniform along the radius but variable in the vertical direction up to the galactic halo where the value of the rms velocity is fixed. The midplane turbulence intensity is the free parameter in the theory, while the density is assumed constant. The (magnetically quenched) turbulent electromotive force is then derived from the given flow pattern. The resulting magnetic fields are generally concentrated in the disk. If, however, the molecular halo diffusivity is small ("hot plasma") and the inner rigidly rotating core is small (thick disks), large toroidal fields are generated in the halo - which are not observed, however. The real galactic dynamo, therefore, works with either vacuum or strong turbulence outside the disk. The calculated magnetic fields resemble the observed ones only if the midplane turbulent velocity slightly exceeds the halo values. Both observed magnetic field strengths and pitch angles are reproduced by the model. The fields increase with thickness of the disk while the pitch angles are proportional to the correlation time of the turbulence ( ≥10⁷ yr). If the midplane rms velocity is drastically increased the dynamo regime tends to switch to the α²-type with increasing magnetic fields and a sudden change to dipolar parity occurs. Even in that case the magnetic fields do not exceed greatly the equipartition values.