Stability of magnetic field inversion regions in spiral galaxies

In some spiral galaxies, the so-called magnetic field inversion regions are observed inside which the field direction is opposite to that in the adjoining regions. Under the differential rotation, the inversion regions should be expected to elongate, to become thinner, and to disappear eventually. It is shown in this paper that the existence of stable inversion regions can be accounted for by modulations of the generation saturation level in spiral arms.