Excitation of large-scale attachment instability in the lower ionosphere under the effect of a high-power radio wave

The propagation of a high-power HF wave in the lower ionosphere is investigated theoretically. It is shown that, in the case of fields comparable with the critical breakdown field, a large-scale self-focusing instability can develop at heights of 100-120 km which is associated with electron attachment to molecules. The characteristic scales and spatial increment of this instability are evaluated.