  Well-known analytical results dealing with ion cyclotron and drift waves and
which follow from the kinetic theory are used and the dispersion equation,
which describes coupled two modes, is solved numerically. The numerical results
obtained by using the values for the plasma density, magnetic field and
temperature applicable to the solar corona clearly show the coupling and the
instability (growing) of the two modes. The coupling happens at very short
wavelengths, that are of the order of the ion gyro radius, and for
characteristic scale lengths of the equilibrium density that are altitude
dependent and may become of the order of only a few meters. The demonstrated
instability of the two coupled modes (driven by the equilibrium density
gradient) is obtained by using a rigorous kinetic theory model and for
realistic parameter values. The physical mechanism which is behind the coupling
is simple and is expected to take place throughout the solar atmosphere and the
solar wind which contain a variety of very elongated density structures of
various sizes. The mode grows on account of the density gradient, it is
essentially an ion mode, and its further dissipation should result in an
increased ion heating.
