Smith, CGA; (2006) Modelling the upper atmosphere of the gas giant planets. Doctoral thesis , UCL (University College London).

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Abstract

At Jupiter and Saturn the thermosphere is the region of the neutral atmosphere that coexists with the ionosphere. It is thus the region of the atmosphere that is most strongly coupled to the magnetosphere, and is responsible via the ionosphere for the transfer of planetary angular momentum to the magnetosphere. Both planets also exhibit high thermospheric temperatures that are yet to be explained. We study the coupled thermosphere-ionosphere-magnetosphere systems of Jupiter and Saturn using a thermospheric general circulation model and simple models of the ionosphere and magnetosphere. Our principle result is that meridional winds in the thermosphere are of critical importance to the interaction. Angular momentum extracted from the thermosphere by magnetospheric drag is found to be replaced largely by meridional advection, not, as commonly supposed, by vertical viscous transfer. These same meridional winds are also able to couple together regions of the magnetosphere that otherwise would not interact. We find it very hard to reproduce the observed thermospheric temperatures with our model. Under a limited range of circumstances it is shown that redistribution of thermal energy from high- to low-latitudes by winds can explain the available observations. However, the inclusion of ion drag generates a circulation in the polar regions that acts as a heat pump and efficiently cools the thermosphere, significantly reducing the efficiency of the redistributive winds.

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