Doppler Profiles of Proton Auroral Emissions Derived From High Resolution FUV Spectra

Abstract

In this paper we present new FUV observations of Doppler-shifted Lyman-ë± emissions from proton aurorae obtained from the High-resolution Ionospheric and Thermospheric Spectrograph (HITS) aboard the Advanced Research and Global Observation Satellite (ARGOS). The Doppler profiles of the Lyman-ë± auroral emissions serve as proxies for the energy spectra of precipitating protons in the ionosphere. These observations remedy two previous shortcomings in proton aurora studies. There have been few spectral measurements of Doppler-shifted H/H[SUP]+[/SUP] emission profiles with which to validate existing models of proton flux transport in the ionosphere. Even fewer are spectral measurements of this kind over large spatial scales that would extend our understanding of proton aurora to a global level. The HITS instrument observes the Doppler shifted H Lyman-ë± emissions from proton precipitation at 0.5 Ì· resolution over the width of the auroral oval traversed by the ARGOS spacecraft. The measured Doppler spectra of proton emissions are then modeled using a Monte Carlo simulation of proton flux transport. The model parameters which include the incoming proton energy, pitch angle, and energy flux distributions are adjusted until the predicted Lyman-ë± Doppler profiles match the observations. This technique allows us to quantify the evolution of proton precipitation during varying levels of auroral activity with both spectral information and large-scale spatial coverage. We present our analysis of proton auroral observations for an isolated substorm event as an example