1996A&A...308..381M

We investigate whether a modulation of the alpha-effect, associated with a density wave in the disc, can promote the generation of bisymmetric magnetic field structure in spiral galaxies. Some calculations where a similar modulation of the non-circular velocity field was imposed are also reported. We adopt a simplified linear galactic dynamo model, applicable to the thin disc limit, but with a full representation of the azimuthal structure, and show that a parametric resonance can occur when the frequency of the imposed spiral wave ω_s satisfies 2ω₀≲ω_s≲4ω₀, where ω₀ is the frequency of the unperturbed bisymmetric dynamo solution. We deduce that parametric resonance may be important in promoting the generation of bisymmetric magnetic field structure in a fraction of `grand design' spiral galaxies.