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

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. Plain Language Summary: The terrestrial auroral display is caused by the collision of energetic particles from space with the Earth's atmosphere. Both energetic electrons and protons can enter the atmosphere and cause auroras, but their transport processes are different. The proton can exchange its charge with atmospheric neutral particles in a collision and become a neutral hydrogen atom, and the hydrogen atom can become a proton again in another collision with atmospheric particles. Both the protons and the hydrogens can ionize the atmospheric neutrals and produce secondary electrons. To model the proton‐induced auroras, the three components, protons, hydrogens, and secondary electrons, must be considered together with their different trajectories and transport in the atmosphere. In this study, we present such a coupled proton‐hydrogen‐electron transport model and simulate the resulting proton auroral intensities. The model results show reasonable agreement with existing ground‐based observations. Key Points: We present a model of coupled proton‐hydrogen‐electron transport in the atmosphere and the resulting auroral excitation and ionizationThe model results show improved agreement with the Hbeta yield reported in existing observations compared to previous modelsOur model can simulate the 557.7 nm emission in proton auroras. The modeled green‐to‐Hbeta ratio is compatible with the existing observation [ABSTRACT FROM AUTHOR]