date: 2012 August 27 (Mon) 14:00-15:00
room: Hokkaido University, Science Bldg. #8, Cosmo-studio
speaker: Chihiro Tao (ISAS)
organizer: Jun Kimura
title: Modeling of Jupiter and Saturn Auroral Emissions
abstract: Planetary aurorae display the dynamic behavior of the plasma surrounding a planet. The outer planetary aurorae are most often observed in the ultraviolet (UV) and the infrared (IR) wavelengths. Modeling of auroral emission is a useful approach to investigate the background physical conditions from auroral emissions. We investigate the sensitivity of UV and IR emissions to the incident precipitating auroral electron energy and flux, and the background atmospheric temperature, and compare the results obtained for Jupiter and Saturn. We develop a model which estimates the UV and IR emission rates accounting for UV absorption by hydrocarbons, ion chemistry, and H_3 ^+ non-local thermodynamic equilibrium (LTE) effects. The dependences of UV and IR emissions on electron flux are found to be similar at Jupiter and Saturn. However, the dependences of the emissions on electron energy are different at the two planets, especially for low energy (<10 keV) electrons; the UV and IR emissions both decrease with decreasing electron energy, but this effect in the IR is less at Saturn than at Jupiter. The temperature sensitivity of the IR emission is also greater at Saturn than at Jupiter. These dependences are interpreted as results of non-LTE effects on the atmospheric temperature and density profiles. Our model also proposes a method for estimating the auroral electron energy from observed H_3 ^+ emission lines at Jupiter. We discuss the applications of our model to observations, such as the different behavior of polar emission at UV and IR wavelengths at Jupiter and Saturn.
keywords: aurora, Jupiter, Saturn, emission model