Topside current instabilities

Both the electrostatic ion acoustic and ion cyclotron waves can be unstable to field-aligned currents comparable to those expected in the auroral zone. However, for a wide range of conditions, the ion cyclotron wave is unstable to the smaller current. In this paper, both instabilities are studied in single and multi-ion plasmas. Profiles of critical current versus height indicate that, as they flow through the topside ionosphere, field-aligned currents of 109–10 electrons/cm2 sec (at 200 km) will destabilize various ion cyclotron waves.