  Nonlinear coupling between 3-minute oscillations and Alfven waves in the
solar lower atmosphere is studied. 3-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-minute oscillations grow exponentially in time near the
layer where the sound and Alfven speeds equal. Thus the 3-minute 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 c_s=v_A may play a role of energy channel
for otherwise trapped acoustic oscillations.
