Magnetic fronts in galaxies

Magnetic-field reversals observed in the Milky Way at one or more Galactocentric radii are interpreted as long-lived transient structures containing memory of the seed magnetic fields. These magnetic fronts can be described using the so-called no-z approximation for the nonlinear, mean-field dynamo equations, which are the topic of the paper. We obtain asymptotic estimates for the speed of propagation of discontinuities in the solution (internal fronts). These estimates agree well with numerical solutions of the no-z equations, and support support our interpretation of the magnetic-field reversals as long-lived transients.