The Impact of Energetic Neutral Particles Raining Down on the Thermosphere due to Charge Exchange Reactions in the Upper Ionosphere and Polar Wind

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The upper atmosphere in the polar regions contains a layer of weakly ionized gas (the ionosphere). Ionized particles such as hydrogen and oxygen ions drift upward in response to heating via electric fields and particle precipitation from the near-Earth space and can reach velocities as high as 10-20 km/s for hydrogen and 3-5 km/s for oxygen. These energetic ions interact with surrounding neutral gas (the thermosphere) and energetic neutral atoms are produced in charge exchange reactions. Light hydrogen atoms escape the atmosphere but heavy neutral species such as oxygen cannot escape and reverse direction. In the polar cap ionosphere-thermosphere system, this gives rise to a continuous Polar Rain. This award will investigate how the energetic neutrals affect circulation, temperature, density, and wave activity in the coupled ionosphere-thermosphere system. The research will contribute to the community effort of modeling of space plasma disturbances by including previously unincluded effects of the energetic neutral particles and by providing a better specification of the required model resolutions. The project will also support a graduate student and contribute to creating a diverse workforce. The work will involve (1) inclusion of new terms in the fluid equations to account for additional types of the ion-neutral and neutral-neutral coupling that are currently not considered, including thermal loss due the energetic atom cooling due to collisions with background neutrals, (2) running a comprehensive set of simulations using the coupled models for various conditions, and (3) investigating effects of different disturbance types.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.