Electron and proton aurora observed spectroscopically in the far ultraviolet

The only way to get a global, instantaneous picture of the energetic particle input over the auroral oval is through spectral imaging. The major driver of auroral emissions in the high‐latitude ionosphere is overall electron precipitation. However, for certain locations and times, such as the equatorial edge of the evening auroral oval, proton precipitation can be the major energy source and thus the primary contributor to auroral emissions. Using kinetic transport models to describe the transport of energetic particles in the atmosphere, we analyze UV spectra from the STP78‐1 satellite mission during magnetically disturbed conditions (Kp = 6) in the evening sector of the auroral oval. We discuss the contribution of protons and electrons to the auroral emissions. The energy flux of the incident protons is inferred from the H Lyman α emissions, after removing the H geocoronal background induced by solar radiation. Both the mean energy and energy flux of electron precipitation are inferred from non‐H emissions (N II 108.5 nm, N2 135.4 nm, and O I 135.6 nm), after removing the contribution of proton precipitation. From the latitudinal distribution of the incident energy flux the location of the electron and proton aurorae is discussed. The estimation of the particle characteristics allows one to infer the Pedersen and Hall electrical conductances induced by particle precipitation. For the studied substorm period, energetic protons contribute significantly to the Pedersen conductance, ∼25–30% overall of the total particle‐induced conductances and much more at the equatorward edge of the midnight aurora. Because protons and electrons do not interact in the same way with the atmosphere, our study shows that while analyzing auroral spectra and studying the state of the ionosphere, it is crucial to separate electron and proton components of the precipitation. The method described to disentangle the relative contribution of precipitating electrons and protons may be applicable to the UV data of the upcoming TIMED and DMSP missions.