High resolution FUV observations of proton aurora

We present new FUV observations of Doppler-shifted Lyman-alpha emissions from proton aurora obtained from the High Resolution Ionospheric and Thermospheric Spectrograph ( HITS) aboard the Advanced Research and Global Observation Satellite (ARGOS). The HITS instrument observes the Doppler-shifted H Lyman-alpha emissions from proton precipitation with 1.5 Angstrom resolution. The high spectral resolution of these measurements allows the auroral Lyman-alpha emissions to be separated from the intense geocoronal background. The measured proton aurora Doppler spectra are modeled using a Monte Carlo simulation of proton flux transport. The forward modeling performed with this code allows us to infer the characteristic energies of the incident protons from the measured Lyman-alpha Doppler spectra. The inferred characteristics of dayside versus nightside proton precipitation are compared and used to identify the magnetospheric regions from which the particles likely originated.