An analysis of pump-induced artificial ionospheric ion upwelling at EISCAT

Ion outflow from the high-latitude ionosphere is a well-known phenomenon and an important source of plasma for the magnetosphere. It is also well known that pumping the ionosphere with high-power high-frequency radio waves causes electron heating. On a few occasions, this has been accompanied by artificially-induced ion upwelling. We analyse such a controlled experiment at EISCAT up to 600 km altitude. The pump-enhanced electron temperatures reached up to ~4000 K above 350 km, and ion upwelling reached up to ~300 m/s above 500 km altitude. The pump-induced electron pressure gradient can explain the ion velocity below 450 km. Between 450 and 600 km the electron pressure gradient correlates equally with ion acceleration and ion velocity, which represents the transition altitude to free ion acceleration. The electron gas pressure gradient can explain ion upwelling, at least up to 600 km altitude. In addition, such active experiments open the possibility to estimating the F-layer ion-neutral collision frequency and neutral density with altitude from ground-based observations.