The Effects of the Polar Rain on the Polar Wind Ion Outflow From the Nightside Ionosphere

Abstract The polar wind, consisting of low‐energy ions and electrons, is an outflow along the open magnetic field lines from the polar cap ionosphere to the magnetosphere. Previous studies found that both solar radiation and solar wind electromagnetic energy are the two main energy sources for the polar wind. The polar rain, being field‐aligned precipitating electrons from the solar wind to the polar cap, may provide additional energies for the polar wind. This scenario is complicated as simulation studies show that polar rain changes the electric potential structures over the polar cap ionosphere. It is unclear how the polar rain affects the polar wind ion outflow. In this study, we show a positive correlation between the polar wind and the polar rain. Meanwhile, the polar wind is generally diminished in regions with strong Earth's magnetic field, suggesting the |B| modulates the penetration depth of the polar rain through the magnetic mirror force and thus the energy dissipation of the polar rain. Therefore, the polar rain can be an additional energy source for the polar wind although the polar rain has generally smaller energies and intensities than the particle precipitations in the auroral regions.