  The joint effect of gravity and thermal misbalance on the dynamics of
acoustic-gravity waves (AGW) in the solar atmosphere is considered. It is shown
that the heating and cooling taken in the form of power functions lead to the
linear dependence of stationary temperature profile. Estimates of the ratio of
the characteristic length associated with thermal processes to the
gravitational height show a predominant influence of thermal processes in the
temperature range up to 2 MK and a comparable influence on the dynamics of AGW
in the range from 2 to 10 MK. A study of the dispersion properties of AGW in an
isothermal atmosphere showed that in regimes with an overwhelming influence of
thermal processes, the acoustic cut-off frequency decreases up to
$\sqrt{\gamma}$ times. At the same time, the maximum frequency of the
gravitational mode (analog of the Brunt-Vaisala frequency in the medium without
non-adiabatic heating and cooling) decreases with increasing power of thermal
processes, and then the gravitational mode can become purely oscillatory.
