The origin of long-period Alfven waves in the solar wind

We suggest that the observed long-period Alfven waves in the solar wind may be generated in the solar interior as a result of the pulsation of the Sun in the fundamental radial mode. The period of this pulsation is about 1 h. The pulsation causes a periodic variation of density and large-scale magnetic field, which affects the Alfven speed in the solar interior. Consequently, Alfven waves with half the frequency of pulsation (i.e. with double the period) can be parametrically amplified in the interior below the convection zone as a result of the recently suggested swing wave-wave interaction. Therefore the amplified Alfven waves have periods of several hours. The waves can propagate upwards through the convection zone to the solar atmosphere and cause the observed long-period Alfven oscillations in the solar wind.