Escape of suprathermal O+ ions in the polar cap

Abstract

Instruments on board the Dynamics Explorer (DE) 1 and 2 spacecraft have been used to investigate the characteristics of a very low‐energy (less than 10 eV) outflow of O+ ions at high altitudes over the polar cap. The measured O+ outflow has a relatively high Mach number (2–6) and a large flux (∼2×108 cm−2 s−1). A statistical study using 50 orbits of retarding ion mass spectrometer (RIMS) data indicates that the outflows occur during active magnetic conditions, lasting for several hours over large areas of the polar cap. The observations are then discussed and analyzed in a framework based on polar wind models with particular attention paid to the new information obtained by the DE 2 Fabry‐Perot interferometer (FPI), and the impact these flows have on the composition of the magnetosphere. The observed suprathermal outflow of O+ suggests a scenario requiring both significant compositional changes in the high latitude thermosphere and significant heating of the ions and electrons in the topside ionosphere.