Polar Wind Observations on the Nightside of the Polar Cap at Altitudes of 2–3 RE: Results of the INTERBALL-2 Satellite

Abstract

The results of measuring the fluxes of ionospheric ions in the nightside polar cap at an altitude of about 20 000 km are presented. The data are obtained with the HYPERBOLOID instrument onboard the INTERBALL-2 satellite. The passages without intense precipitation of magnetospheric ions and electrons have been selected using the ION instrument data, so that the observation of ionospheric ion fluxes caused by heating in the auroral regions can be excluded. In addition, an attempt has been made to exclude observations of the “cleft ion fountain” from the analysis. The measurements in the summer and winter seasons (when the ionosphere was totally sunlit and completely shadowed, respectively) are considered separately. By analyzing the distribution functions of the fluxes measured, we have isolated six different types of ionospheric plasma flows in the polar cap. A strong distinction has been revealed between summer and winter flows. In winter, only weak flows of H+ ions were detected. In the summer period, we detected both H+ and O+ ions. The flux values of the ionosphere ions are found to be strongly dependent on the intensity of the polar rain. The measurements are compared to the existing models of the polar wind. The best models (for the description of our measurements) are indicated. After the choice of measurement periods, the resulting region coincides with the ion depletion zone (IDZ). Based on the earlier measurements by the AKEBONO satellite, nothing could be said about the fluxes of thermal ions in this zone, because of the insufficient sensitivity of the instrument aboard this satellite.