Counterstreaming of O+ and H+ ions in the plasmasphere

Although the ion flux along plasmaspheric flux tubes has been both measured and numerically modeled for many years, it is only recently that H+-O+ counterstreaming, with O+ upwards, has been encountered experimentally and studied theoretically. The theoretical studies indicate that counterstreaming occurs under special conditions which occur primarily near twilight. In this paper we show that such counterstreaming arises not only from a combination of several particular conditions but is a more fundamental characteristic of the flow of plasma in the closed field-line magnetosphere. We analyzed the causes of counterstreaming and show that the phenomenon must occur under steady state conditions. We then examine how diurnal variations modify the steady state pattern