Downward propagating ionization structures observed by UHF radar scattering of HF-enhanced ion-lines at the HAARP ionospheric-modification facility

The MUIR UHF radar at the HAARP ionospheric modification facility has been operated in a number of experiments where the HF-enhanced ion-line has been used to monitor the ionospheric density variations. The altitude of the enhanced ion-line signals moves downward in response to increasing electron density variations that result from temperature-dependent ion chemistry, and for the special gyro-resonant case additional ionization is produced due to local electron acceleration near the altitude of the ion-line signals. The characteristics of these signals and their relation to optical emissions and model results will be presented.