  We consider the parametric excitation of Alfven waves by gravitational
radiation propagating on a Minkowski background, parallel to an external
magnetic field. As a starting point, standard ideal MHD equations incorporating
the curvature of space-time has been derived. The growth rate of the Alfven
waves has been calculated, using the normal mode approach. Various
astrophysical applications of our investigations are discussed, and finally we
demonstrate that the coupling coefficients of the interacting modes fulfill the
Manley-Rowe relations.
