  The importance of the Jovian thermosphere with regard to
magnetosphere-ionosphere coupling is often neglected in magnetospheric physics.
We present the first study to investigate the response of the Jovian
thermosphere to transient variations in solar wind dynamic pressure, using an
azimuthally symmetric global circulation model coupled to a simple
magnetosphere and fixed auroral conductivity model. In our simulations, the
Jovian magnetosphere encounters a solar wind shock or rarefaction region and is
subsequently compressed or expanded. We present the ensuing response of the
coupling currents, thermospheric flows, heating and cooling terms, and the
aurora to these transient events. Transient compressions cause the reversal,
with respect to steady state, of magnetosphere-ionosphere coupling currents and
momentum transfer between the thermosphere and magnetosphere. They also cause
at least a factor of two increase in the Joule heating rate. Ion drag
significantly changes the kinetic energy of the thermospheric neutrals
depending on whether the magnetosphere is compressed or expanded. Local
temperature variations appear between ~ -45 and 175 K for the compression
scenario and ~ -20 and 50 K for the expansion case. Extended regions of
equatorward flow develop in the wake of compression events - we discuss the
implications of this behaviour for global energy transport. Both compressions
and expansions lead to a ~ 2000 TW increase in the total power dissipated or
deposited in the thermosphere. In terms of auroral processes, transient
compressions increase main oval UV emission by a factor of 4.5 whilst transient
expansions increase this main emission by a more modest 37%. Both types of
transient event cause shifts in the position of the main oval, of up to 1 deg
latitude.
