SWING COUPLING BETWEEN FAST MAGNETOSONIC AND ALFVEN WAVES

摘要

We suggest a mechanism of energy transformation from fast magnetosonic waves propagating in homogeneous medium across a uniform magnetic field to Alfven waves propagating along the field. The mechanism is based on swing wave-wave interaction [T.V. Zaqarashvili, Astrophys. J. Lett. 552, 107 (2001)]. The standing fast magnetosonic waves cause a periodical variation in the Alfven speed, with the amplitude of an Alfven wave being governed by Mathieu's equation. Consequently, sub-harmonics of Alfven waves with a frequency half that of magnetosonic waves grow exponentially in time. It is suggested that the energy of nonelectromagnetic forces, which axe able to support the magnetosonic oscillations, may be transmitted into the energy of purely magnetic oscillations. Possible astrophysical applications of the mechanism are briefly discussed.