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Modulation of Jupiter's plasma flow, polar currents, and auroral precipitation by solar wind-induced compressions and expansions of the magnetosphere: a simple theoretical model

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journal contribution
posted on 31.10.2016, 15:47 by S. W. H. Cowley, J. D. Nichols, D. J. Andrews
We construct a simple model of the plasma flow, magnetosphere-ionosphere coupling currents, and auroral precipitation in Jupiter's magnetosphere, and examine how they respond to compressions and expansions of the system induced by changes in solar wind dynamic pressure. The main simplifying assumption is axi-symmetry, the system being modelled principally to reflect dayside conditions. The model thus describes three magnetospheric regions, namely the middle and outer magnetosphere on closed magnetic field lines bounded by the magnetopause, together with a region of open field lines mapping to the tail. The calculations assume that the system is initially in a state of steady diffusive outflow of iogenic plasma with a particular equatorial magnetopause radius, and that the magnetopause then moves rapidly in or out due to a change in the solar wind dynamic pressure. If the change is sufficiently rapid (~2–3 h or less) the plasma angular momentum is conserved during the excursion, allowing the modified plasma angular velocity to be calculated from the radial displacement of the field lines, together with the modified magnetosphere-ionosphere coupling currents and auroral precipitation. The properties of these transient states are compared with those of the steady states to which they revert over intervals of ~1–2 days. Results are shown for rapid compressions of the system from an initially expanded state typical of a solar wind rarefaction region, illustrating the reduction in total precipitating electron power that occurs for modest compressions, followed by partial recovery in the emergent steady state. For major compressions, however, typical of the onset of a solar wind compression region, a brightened transient state occurs in which super-rotation is induced on closed field lines, resulting in a reversal in sense of the usual magnetosphere-ionosphere coupling current system. Current system reversal results in accelerated auroral electron precipitation occurring in the outer magnetosphere region rather than in the middle magnetosphere as is usual, with peak energy fluxes occurring just poleward of the boundary between the outer and middle magnetosphere. Plasma sub-corotation is then re-established as steady-state conditions re-emerge, together with the usual sense of flow of the closed field current system and renewed but weakened accelerated electron precipitation in the middle magnetosphere. Results for rapid expansions of the system from an initially compressed state typical of a solar wind compression region are also shown, illustrating the enhancement in precipitating electron power that occurs in the transient state, followed by partial reduction as steady conditions re-emerge.

History

Citation

Annales Geophysicae, 2007, 25 (6), pp. 1433-1463 (31)

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Annales Geophysicae

Publisher

European Geosciences Union (EGU), Copernicus Publications, Springer Verlag

issn

0992-7689

eissn

1432-0576

Acceptance date

24/05/2007

Available date

31/10/2016

Publisher version

http://www.ann-geophys.net/25/1433/2007/

Language

en