Resonant energy conversion of 3-min intensity oscillations into Alfven waves in the solar atmosphere

Nonlinear coupling between 3-min oscillations and Alfven waves in the solar lower atmosphere is studied. Three-minute oscillations are considered as acoustic waves trapped in a chromospheric cavity and oscillating along transversally inhomogeneous vertical magnetic field. It is shown that under the action of the oscillations the temporal dynamics of Alfven waves is governed by Mathieu equation. Consequently, the harmonics of Alfven waves with twice period and wavelength of 3-min oscillations grow exponentially in time near the layer where the sound and Alfven speeds equal i.e. c(s) approximate to v(A). Thus the 3-min oscillations are resonantly absorbed by pure Alfven waves near this resonant layer. The resonant Alfven waves may penetrate into the solar corona taking energy from the chromosphere. Therefore the layer cs approximate to v(A) may play a role of energy channel for otherwise trapped acoustic oscillations. (C) 2007 Elsevier Ltd. All rights reserved.