H+ ion acceleration in the mid‐altitude ionosphere

Abstract

H+ ion acceleration by electromagnetic ion cyclotron waves in the Earth's mid‐altitude (300 to 2000 km) ionosphere is investigated. Below about 800 km, the ionospheric density is sufficiently high to induce significant collision rates between thermal particles and accelerated H+ ions. The dominant collisions are associated with ion‐ion Coulomb interactions and with charge exchange reactions of the type H+ + A → H + A+. These reactions are able to substantially modify the space and velocity distribution of the accelerated H+ ions. Using Monte‐Carlo simulations, it is shown that the combination of collisions and ion cyclotron acceleration produces energetic H+ ion distributions whose characteristics (flux, average energy and pitch angle) are in quantitative agreement with satellite observations. The distributions of the energetic H atoms which are produced by charge exchange and which might be used for remote sensing of such H+ ion acceleration processes, are also presented.