Heating of ions to superthermal energies in the topside ionosphere by electrostatic ion cyclotron waves

Abstract

The soft particle spectrometer on the Isis 2 spacecraft, which is in a nearly circular orbit at 1400‐km altitude, frequently observes fluxes of upcoming ions with a conical pitch angle distribution and pitch angles usually in the range 90°–135°. The upcoming ions are usually observed near the boundaries of the auroral precipitation zone and primarily in the winter nighttime at the Isis 2 altitude. The observations are interpreted in terms of electrostatic ion cyclotron waves, which heat the ions to superthermal energies transverse to the earth's magnetic field. Subsequently, the ions are accelerated away from the earth by the earth's magnetic field.