Resonant conversion of standing acoustic oscillations into Alfv{é}n waves in the $β~ 1$ region of the solar atmosphere

Abstract

We show that 5-minute acoustic oscillations may resonantly convert into Alfv{é}n waves in the $β{\sim}1$ region of the solar atmosphere. Considering the 5-minute oscillations as pumping standing acoustic waves oscillating along unperturbed vertical magnetic field, we find on solving the ideal MHD equations that amplitudes of Alfv{é}n waves with twice the period and wavelength of acoustic waves exponentially grow in time when the sound and Alfv{é}n speeds are equal, i.e. $c_s \approx v_A$. The region of the solar atmosphere where this equality takes place we call a {\it swing layer}. The amplified Alfv{é}n waves may easily pass through the chromosphere and transition region carrying the energy of p-modes into the corona.