| 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+). Energetic neutral atoms (ENAs) are produced in charge exchange reactions between singly ionized polar wind ions and the surrounding neutral atoms. Recent estimates for neutral outflow integrated fluxes from the LENA instrument on the IMAGE spacecraft have shown values of 1-4x109 cm-2s -1, with a considerable diurnal variation, in agreement with 1-dimensional model results showing a high neutral hydrogen outflow flux on the order of 109 cm-2s-1.; The neutral polar wind shows a highly dynamic structure, with polar wind ions highly dependent on convection electric fields, with outflow dynamics modified by the heat input of precipitating electrons. A new 3-dimensional model of the neutral polar wind has been developed, which takes into account convection, heating due to precipitating electrons, and charge exchange. The results show large neutral polar wind fluxes in both the horizontal and vertical directions, with heating that occurs during geomagnetic storms leading to a significant coupling between the ionosphere and magnetosphere via both ion and neutral particles.; The characteristics of the neutral polar wind are highly dependent upon the ions in the high-latitude polar cap. The ions are convected across the polar cap due to convection electric fields, and thus the neutral stream particles are also indirectly affected by the convection electric fields due to charge exchange. The horizontal flow of neutral stream particles, therefore, shows a general anti-sunward motion during periods of southward IMF, and a general sunward flow across the magnetic pole during times of northward IMF. The vertical fluxes of these neutral stream particles depend upon the heat input due to precipitating electrons, the vertical velocity of the ions involved in the charge exchange reactions that produce the neutral stream particles, and the time history of the neutral particles in the high-latitude polar cap region. |
