  The weakly non-linear interaction of slow magnetoacoustic and torsional
Alfven waves propagating along an unperturbed poloidal magnetic field in a
stellar interior is studied in the high plasma beta limit. It is shown that
slow magnetoacoustic waves parametrically drive torsional modes with the half
frequency and wave number. Therefore global slow magnetoacoustic waves which
have a radial velocity polarization, may amplify the torsional oscillations.
Possible applications of this mechanism to the Sun and binary stars are briefly
discussed.
