Yates, JN; (2013) Influence of solar wind on the Jovian thermosphere. Doctoral thesis (PhD), UCL (University College London).

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Abstract

We aim to explain the reason why Jupiter's upper atmosphere is hotter than initial theories predicted by employing a coupled magnetosphere, ionosphere and thermosphere model. We use this coupled model to study how changes in upstream solar wind dynamic pressure affect Jupiter's thermospheric dynamics, energy balance, aurora and magnetosphere-ionosphere coupling currents. The variation in solar wind pressure is investigated on long (_50 Jovian days) and short (3 hours) time scales, which we respectively refer to as steady state and transient state. We vary the solar wind pressure by changing the size of the magnetosphere, as these two parameters are inversely correlated. In steady state, three different configurations are used: compressed, average and expanded magnetospheres. We find that the power dissipated by Joule heating and ion drag increases by —190% from a compressed to expanded magnetosphere. For transient modelling, the magnetosphere is compressed and expanded in a period of 3 hours. Compressions cause a reversal in momentum transfer between the thermosphere and magnetosphere. Compressions and expansions lead to at least a factor-of-two increase in ion drag and Joule heating, resulting in a —2000 TW increase in total power dissipated in the thermosphere and local temperature variations 25 K. Compressions also cause a —450% increase in auroral UV emission whilst expansions increase UV emission modestly by —37%. While these analyses do not provide a definitive answer to the elevated Jovian thermospheric temperature, they show that, in moving from a steady-state to a time-dependent paradigm, the thermospheric response to magnetospheric reconfiguration is characterised by dramatically different distributions of temperature and wind. In particular, magnetospheric compressions produce extensive cells of equatorward flow emanating from the auroral zone, suggesting that a Jovian-like magnetosphere subject to adequately frequent, repeated episodes of contraction/expansion may possess elevated thermospheric temperatures, perhaps even at the level of those observed.

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