Universität zu Köln

Jacobsen, Sven (2011). Three-dimensional magnetohydrodynamic simulations of Io's non-linear interaction with the Jovian magnetosphere. PhD thesis, Universität zu Köln.

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Abstract

For the present dissertation an advanced three-dimensional MHD model has been developed to investigate the interaction of Io with the Jovian magnetosphere. The interrelation we study in the present work originates from the relative movement of a satellite with respect to the surrounding magnetic field and magnetospheric plasma. Several phenomena like auroral, radio emissions and energetic electron beams are associated with such interaction. The type of interaction is common in the Jovian system. Besides Io, other Galilean moons like Europa and Ganymede likewise interact with the surrounding magnetoplasma. Moreover Saturn's moon Enceladus exhibits similar interplay. Hence, the plasmaphysical satellite-planet interaction, best known for Io, is most likely common in the universe and thus worthwhile to be closely investigated. Io's relative motion in the plasma torus perturbs the magnetospheric plasma. The generated plasma waves are partly reflected at plasma density gradients, but also at the auroral acceleration region. The result is a complex and fluctuating wave pattern located downstream of Io. This is documented by the highly structured auroral imprint of this pattern which was found to exhibit considerable temporal variations. Another consequence of the electromagnetic interaction of Io with the magnetoplasma is the generation of trans-hemispheric energetic electron beams in the auroral acceleration region. These beams have been detected in-situ in the equatorial plane by the Galileo probe. Auroral spots in the conjugate hemisphere associated with these beams were also identified remotely in HST observations. They have the outstanding property, that they are, other than the reflection associated footprint pattern, sometimes located upstream of the main Io footprint. However, also this position was found to vary notably. Partly the variations of Io's imprint in the aurora can be described, by Io's oscillation in the plasma torus. Yet, this concept cannot explain all observations. In order to study the interaction system in detail, we enhance an ideal MHD model by incorporating an effective collision frequency to account for Io's interaction with the incoming plasma. Moreover, we implement resistivity in order to allow for the potential drop in the auroral acceleration region. Different plasma density domains represent the various plasma regimes along the travel path of the waves. We investigate how and to what extent different factors influence the Io footprint morphology and conclude that particularly the interaction strength has an impact on the reflection geometry and thus on the footprint pattern. Our results agree qualitatively with observational findings. Our model allows furthermore to deduce locations of equatorial electron beams. The results match the locations of actual beam detections by Galileo. We also present a separate model to estimate inter-spot distances and compare our predictions to both, the observations and the Simulation results. Besides to Io, we apply our model to the interaction of Enceladus with Saturn. We weight the possibility of Alfven wave reflection in this particular case, and find possible evidence for a reflected Alfven wave signature in the Cassini magnetic field observations. We support this hypotheses by results obtained with our numerical model.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Jacobsen, Sven svenjacobsen@gmx.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-42676
Date:	27 June 2011
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology
Subjects:	Data processing Computer science Natural sciences and mathematics Physics Earth sciences
Uncontrolled Keywords:	Keywords Language Alfven Waves, Reflection, Magnetosphere, Aurora, Io, Jupiter, Footprint, Electron Beams, Enceladus, E4, magnetohydrodynamic, MHD, Simulation English
Date of oral exam:	19 May 2011
Referee:	Name Academic Title Saur, Joachim Prof. Dr. Neubauer, Fritz M. Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/4267