Neutral polar wind

Abstract

The classical polar wind is an ambipolar outflow of ions from high latitudes along open geomagnetic field lines. The polar wind consists of light thermal ions (H+, He+) and energetic light and heavy ions (H+, He+, O+). The characteristics of these ions have been studied quite extensively since the 1960s. In just the last 20 years, however, energetic neutral atoms (ENAs) that are produced in charge exchange reactions between the singly ionized polar wind ions and the surrounding neutral atoms have been used as a means to remotely probe plasma populations. Recent estimates for neutral outflow integrated fluxes from the LENA instrument on the IMAGE spacecraft have shown values of 1–4 × 109 cm−2 s−1, with a considerable diurnal variation. A theoretical model has been used in this study that is similar to the high‐latitude hydrodynamic polar wind model developed at Utah State University, but it has been expanded to include the effects of neutral stream particles so that the characteristics of the neutral polar wind can be elucidated. The neutral polar wind model results show a high neutral hydrogen outflow flux on the order of 109 cm−2 s−1.