Simultaneous bistatic European Incoherent Scatter UHF, 145‐MHz radar and stimulated electromagnetic emission observations during HF ionospheric modification

The ionosphere was modified with powerful, high‐frequency radio waves transmitted by the Heating facility near Tromsø, Norway. The modified ionosphere was observed using the Tromsø and Kiruna European Incoherent Scatter (EISCAT) UHF system together with a 145‐MHz portable CW radar and equipment for reception of stimulated electromagnetic emissions (SEE). Enhanced ion and plasma lines were observed. They persisted throughout heater periods of more than a minute, contrary to earlier observations at Tromsø. Spectral features in the plasma lines were repeatedly observed at frequency shifts which are not explained by current theories. The SEE amplitude variation on long time scale (seconds to tens of seconds) shows similarity with the long–time scale behavior of the amplitude of the plasma lines observed by EISCAT. No obvious correlation seems to exist between the SEE and discovered radar spectral features.