  It is generally accepted that the ion acoustic (IA) wave in plasmas
containing ions and electrons with the same temperature is of minor importance
due to strong damping of the wave by hot resonant ions. In this work it will be
shown that the IA wave is susceptible to excitation even in plasmas with hot
ions when both an electromagnetic transverse wave and a background density
gradient are present in the plasma, and in addition the wave is in fact
unstable (i.e., growing) in the case of permeating homogeneous plasmas. The
multi-component fluid theory is used to describe the IA wave susceptibility for
excitation in inhomogeneous plasmas and its coupling with electromagnetic
waves. The growing IA wave in permeating homogeneous plasmas is described by
the kinetic theory. In plasmas with density and temperature gradients the IA
wave is effectively coupled with the electromagnetic waves. In comparison to
ordinary IA wave in homogeneous plasma, the Landau damping of the present wave
is much smaller, and to demonstrate this effect a simple but accurate fluid
model is presented for the Landau damping. In the case of permeating plasmas, a
kinetic mechanism for the current-less IA wave instability is presented, with a
very low threshold for excitation as compared with ordinary
electron-current-driven kinetic instability. Such growing IA waves can
effectively heat plasma in the upper solar atmosphere by a stochastic heating
mechanism presented in the work. The results of this work suggest that the IA
wave role in the heating of the solar atmosphere (chromosphere and corona)
should be reexamined.

Plasma Physics;Solar and Stellar Astrophysics;Space Physics