Numerical models of the galactic dynamo driven by supernovae and superbubbles

We calculate the temporal evolution and spatial structure of the large-scal e magnetic field in our Galaxy, in the framework of an axisymmetric SN-driv en dynamo model. We consider various parameter regimes, allowing for anisot ropies in the dynamo parameters, the existence of an effective vertical esc ape of the field (analogous to a Galactic wind carrying field lines away fr om the midplane), vertical variations in the Galactic rotation curve... In the linear regime, axisymmetric (m = 0) modes are always easier to excit e than bisymmetric (m = 1) modes. Amongst the former, the even (SO) mode of ten has the larger growth rate, while the odd (AO) mode generally oscillate s more readily. Under typical conditions, the SO and AO modes have very sim ilar properties; both grow monotonically with time at an exponential rate s imilar or equal to 0.45 Gyr(-1), which suggests that the Galactic magnetic field has presently reached a state close to saturation. In the absence of vertical escape, the magnetic field oscillates and only its AO component is amplified. Oscillatory behaviors are also found when the azimuthal alpha-p arameter is enhanced by at least a factor of 3 or when the magnetic diffusi vities are reduced by a factor > 1.7 with respect to their reference values ; in both cases, the switch from monotonous to oscillatory behavior is acco mpanied by an increase in the growth rate. A height-dependence in the Galac tic rotation velocity profoundly modifies the magnetic field morphology and is conducive to oscillatory decay. The nonlinear solutions obtained when the dynamo parameters are forced to d ecrease with increasing magnetic field strength are generally more spread o ut in space. For the growing modes, the field amplification saturates when its intensity in the peak region reaches similar to 20 mu G, corresponding to a magnetic pressure of roughly four times the local gas pressure. The ti me to saturation, which depends on the seed field strength adopted, is typi cally of the order of a few 10 Gyr. Nonlinear mode interactions may produce long-term changes both in the even vs. odd parity and in the monotonous vs . oscillatory temporal behavior of the large-scale magnetic field.