Observation of a two-temperature ion energy distribution in regions of polar wind flow

In many regions of the ionosphere the distribution functions of the particles are highly time dependent because of the variation in energy deposition and particle ionization rates. At present, it is recognized that the electrons, the ions, and the neutral gases exist at three generally distinct temperatures that approach one another at low altitudes, where the mutual collision frequencies are sufficiently high. In the high-latitude region, and especially at higher altitudes, a greater deviation from equilibrium is expected as a consequence of the complex flow patterns of ionization, downward energy conduction, and mass flow. In this work we begin a study of deviations from thermal equilibrium among the ions by considering that the ‘light’ ions H+ and He+ may be at a different temperature from the ‘heavy’ ion O+. Further, we study in particular the case in which thermal protons are observed to be flowing relative to the assumed static ambient oxygen ions. The proton flow is assumed to be along the direction of the magnetic field. Of the cases tested, it is found that the measured proton temperature is from 1 to 10 times the measured oxygen ion temperature. Such temperature enhancements may be expected both because of the energy transfer associated with the ion flow and as a consequence of the preferential energy coupling from the light ion distribution in the exosphere.