A self‐consistent model of the Jovian auroral thermal structure

A one-dimensional (1-D) model coupling a two-stream electron transport model of energy deposition with a 1-D thermal conduction model has been developed. It is applied to investigate the links between auroral heat input and the vertical temperature of Jupiter's upper atmosphere. Two energy distributions meant to reproduce the emissions of a diffuse and a discrete aurora are used to evaluate the importance of the energy spectrum of the incident electrons for the thermal balance of Jupiter's auroral thermosphere. The values of observable quantities such as the altitude of the H2 emission peak, thermal infrared (IR), ultraviolet (UV) emissions, and temperatures associated with various optical signatures are used to constrain the parameters of these distributions. It is shown that the high-energy component of these energy distributions heats a region of the homosphere between 10−4 and 10−6 bar and mainly controls the H2 temperature and the far-UV (FUV) emission. A 3-keV soft electron component is necessary to heat the region directly above the homopause, between 10−6 and 10−9 bar. It has a large influence on the H2 and H3+ temperatures and on the H3+ near-IR (NIR) emission. It is used in conjunction with a weak 100 eV component which is responsible for heating the thermosphere, from 10−9 to 10−12 bar and exerts a control on the exospheric temperature. The calculated temperatures, UV, and IR emissions suggest that the model probably misses a nonparticle heat source in the 10−5 bar region, that is expected to balance the strong hydrocarbon cooling. Sensitivity tests are performed to evaluate the importance of the parameters of the energy distributions. They show that the FUV color ratio increases with the characteristic energy (or high-energy cutoff) of the high-energy component, while the H2 rovibrational temperature varies inversely. A trade-off is therefore necessary for these two parameters to simultaneously meet their observational constraints. Further tests demonstrate the essential thermostatic role played by H3+, which regulates the net heating in the thermosphere. An increased eddy diffusion reproduces the effect of a possible auroral upwelling of methane but gives rise to an H2 temperature smaller than the observed value.

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