Heater-induced phenomena in a coupled ionosphere–magnetosphere system Original Research Article

Experimental results from HF pumping experiments in the nightside auroral E and F region are reported. The experiments were carried out by the use of the EISCAT HF heating facility located near Tromsø, Norway, allowing HF pumping the ionosphere in a near magnetic field-aligned direction. We present experimental results from multi-instrument observations related to heater-induced phenomena in a coupled ionosphere–magnetosphere system. The following results have been observed on different occasions: a reverberation effect in scattered signals observed simultaneously on two diagnostic paths which is an indication of Alfvén wave generation. This phenomenon was seen under specific disturbed background geophysical conditions, namely, a high electron density in the F region up to 8 MHz produced by soft electron precipitation from the magnetosphere along with low electron density in lower ionosphere; increased ionospheric electric fields; ion outflows from the ionosphere. On another occasion a magnetospheric response to heater turning on and off was found from magnetic pulsation observations over a frequency range up to 5 Hz (the upper frequency limit of the sensitive magnetometer at Kilpisjarvi, located near Tromsø). The response manifests itself about 1 min after the heater is turned on and off. Other results have shown the modification of a natural auroral arc and local spiral-like formation. It is thought that a local heater-driven current system is formed. An interesting feature is the generation of the heater-induced ion outflows from the ionosphere. They are observed in night hours under both quiet and disturbed magnetic conditions.