Resonance instability of small‐scale field‐aligned irregularities

The generation of small‐scale field‐aligned irregularities in ionospheric heating experiments is explained in terms of a purely growing parametric instability with thermal coupling based on the scattering of the pump field by the irregularities into plasma oscillations. The standing wave nature of the pump field is a necessary aspect of the present instability which does not require the previous presence of nonthermal irregularities.