Ion-neutral interactions in arctic upper atmosphere observed with EISCAT3D

Electric currents and particle precipitation heat the polar upper atmosphere, leading to changes in its chemical composition and density. The density variations are critical for low-Earth orbit satellites and space debris tracking. The heating is strongest below 200 km altitude, where strong atmospheric drag prevents satellite operations. The atmospheric region critical to technological systems that our society relies on must thus be observed only remotely. The next-generation EISCAT3D radar system will be soon available for scientific observations. The radar observes only the ionized particles that form the ionosphere around 70-1000 km altitudes, but properties of the neutral particles can be deduced from those of the ions, because the two populations interact via collisions and chemical reactions. We develop new tools that enable radar observations of ion composition and ion-neutral collision frequency, which enables studies of the neutral upper atmosphere with EISCAT3D, and use these tools for studies of space weather effects on the Earth's upper atmosphere and near-Earth space.