Thermal self-focusing instability in the high-latitude ionosphere

A model for the linear theory of the overdense thermal self‐focusing instability, as generated by high power radio waves, in the high‐latitude F‐region ionosphere is developed. We treat self‐focusing‐driven irregularities with scale sizes, perpendicular to the geomagnetic field, on the order of a kilometer and smaller. We find that E‐region coupling leads to nonambipolar perpendicular diffusive effects. The conducting E‐region is shown to increase the threshold for the thermal self‐focusing instability. Growth rates of the thermal self‐focusing instability are computed, including E‐region conductivity effects, for a range of radio wave amplitudes.