IMAGE-FUV observations and modeling of proton-induced aurora

Observations made with the Wide-Band Imaging Camera (WIC) and the Spectrographic Imagers (SI) on board the IMAGE satellite make it possible to spectrally discriminate between proton and electron FUV aurora. They clearly show that electron and proton precipitations largely overlap. However, images of the Doppler-shifted Lyman-$\alpha$ emission show regions such as the pre-midnight low latitude sector where proton precipitation is generally separated from the electron component. Simulations based on the statistical DMSP satellite measurements of electron and proton precipitation have been made to calculate the induced FUV emissions. Auroral Lyman-α is solely excited by energetic protons suffering charge exchange collisions. Lyman-α emission rates and line profiles are calculated with a Direct Monte Carlo Method. They indicate that, at most locations, N2 LBH and OI 135.6 nm excitation is dominated by primary and secondary electrons. Only at certain local times and latitudes do protons and their secondary electrons add a significant contribution to these emissions. Comparison will be presented between the expected morphology and brigthness distribution based on the statistical particle measurements and IMAGE FUV observations. Large upward fluxes of fast hydrogen atoms due to magnetic mirroring, geometric spreading and collisional scattering of the precipitated protons are predicted above regions of strong proton precipitation.