Modulation instability at the upper hybrid layer in high‐power radio wave ionospheric heating

A model of the evolution of finite amplitude upper hybrid waves generated at the upper hybrid resonance height during high‐power radio wave ionospheric heating is presented. We show that the threshold for modulation instability can be exceeded for upper hybrid wave amplitudes of the order of a few tens of millivolts per meter and will be excited for scale sizes, perpendicular to the geomagnetic field, of the order of a few tens of electron gyroradii.