Chemistry of the Jovian Auroral Thermosphere/Ionosphere

We have modeled the chemistry of the Jovian auroral themosphere/ionosphere by carrying out multistream electron-transport calculations for a standard model based on pressure and temperature data from Galileo, and two additional models that are characterized by enhanced eddy diffusion coefficients. We have modeled the precipitation of electrons for several energies between 20 and 100 keV with energy fluxes of about 10 erg cm ^-2 \rm s ^-1 . We have derived the column densities of H ₂ , H, CH ₄ and C ₂ H ₂ at the altitudes of peak energy deposition. For methane column densities similar to those determined by IUE and HST data, we find that for our standard model, the most likely electron energies are in the 45-55 keV range. For the enhanced eddy diffusion models, the energies are lower. We present ion profiles, H density profiles, and production profiles for the most important H ₂ and H emissions. The predicted H column densities are in the range (1-6) x 10 ¹⁸ cm ^-2 for the standard model, and are smaller for the enhanced eddy diffusion models. We also find that the temperatures near the altitude of peak energy deposition vary from 160 to 200 K, and are much lower than those derived from rotational analyses of auroral H ₂ emissions. This indicates that the auroral thermosphere is warmer than that at equatorial or midlatitudes.