Modeling of Diffuse Aurora due to Precipitation of H~+-H and SEP Electrons in the Nighttime Atmosphere of Mars: Monte Carlo Simulation and MAVEN Observation

摘要

The nighttime limb intensity of diffuse auroral emission of CO_2~+ (B~2Σ_u~+ - X~2π_g) Ultraviolet Doublet (UVD) is observed in the northern hemisphere of Mars during 17-21 December 2014 from Imaging Ultraviolet Spectrograph instrument onboard Mars Atmosphere and Volatile Evolution. We have used hybrid model and four-dimensional yield spectrum approach based on Monte Carlo simulation to calculate the ionization rate, limb intensity, and ion and electron densities of diffuse aurora due to precipitation of solar energetic particle and proton-hydrogen (H~+-H) fluxes in the nighttime ionosphere of Mars. It is found that the production rates of atmospheric ions (CO_2~+, N_2~+, and O~+) are dominant in the upper ionosphere at about 100-150 km due to impact of H~+-H. The solar energetic particle formed auroral ionosphere (CO_2~+, NO~+, and O~+) in the middle ionosphere between 50 and 100 km due to precipitation of monoenergetic electrons of energies 25 to 100 keV. The simulated limb intensities of CO_2~+UVD due to impact of H~+-H and auroral electrons are compared with Imaging Ultraviolet Spectrograph observations. Our model results are overestimating the observations, but 100 keV electrons deposited maximum energy around 75 km, closer to the observed altitude of the maximum emission. The densities of upper ionosphere (O_2~+, NO~+, and CO_2~+) due to impact of H~+-H are smaller by one to two orders of magnitude than that produced by auroral electrons in the middle ionosphere.