A New Proton-Hydrogen-Electron Transport Model for Simulating Optical Emissions From Proton Aurora and Comparison With Ground Observations

Abstract

Energetic proton precipitation from the magnetosphere plays an important role in the magnetosphere-ionosphere-thermosphere coupling and energy transfer. Proton precipitation causes hydrogen emissions, such as Hβ (486.1 nm), and also triggers the excitation of other emission lines such as the blue-line (427.8 nm) and the green-line (557.7 nm). In light of the growing availability of ground-based proton auroral measurements in recent years, we revisit the proton auroral modeling in this study, with more focus on the application for interpreting ground observations. An accurate simulation of these optical emissions requires a comprehensive understanding of particle transport and collisions in the upper atmosphere, where the simultaneous consideration of precipitating protons, newly generated energetic hydrogen atoms, and secondary electrons is critical. For this purpose, we couple a 3D Monte-Carlo proton transport model and an electron transport model. The integrated model framework can compute the emission rates of most major auroral emission lines/bands resulting from proton precipitation, along with self-consistent calculation of the ionospheric electron density variations. The model results show improved agreement with ground optical observations in terms of the Hβ yield and the green-to-Hβ ratio compared to previous model studies. Our new model is a valuable tool for quantifying excitation and ionization due to proton aurora. It has the potential to leverage ground observations to infer precipitating conditions at high altitudes and even for studying magnetospheric activity.