Contrasting O/X-mode heater effects on O-mode sounding echo and the generation of magnetic pulsations

The effects on the ionosphere of powerful O-mode and X-mode HF pump waves, modulated 3 minutes on and 1 minute off, were explored. The experiments were monitored using the digisonde and magnetometer located at the HAARP facility. The results show that the virtual heights of the O-mode sounding echoes shifted down/up as the O/X mode heater was turned on; the ionosphere also moved downward/upward accordingly. Enhanced spread-F was also observed in O-mode heater-on periods. Heater-induced magnetic pulsation was observed. Its intensity increased progressively in the heater on/off sequence and X-mode heater was more effective than O-mode heater in the generation of magnetic pulsation. In the last X-mode heater-on period, when the magnetic pulsation reached the highest level, pc 3 pulsations, with increasing intensity were also observed.