Schilling, Nico (2006) Time varying Interaction of Europa's Atmosphere-Ionosphere and its Conducting Ocean with the Jovian Magnetosphere. PhD thesis, Universität zu Köln.
A time-dependent 3D magnetohydrodynamic (MHD) model has been developed to investigate the temporal periodic interaction between Europa and the Jovian magnetosphere. The temporal variations are caused by the periodic variations of the magnetospheric plasma at Europa. As a new feature compared to existing stationary models, periodic induced magnetic fields, caused by electromagnetic induction in a potential subsurface ocean, are included. The MHD-flow problem and the internal induction problem are solved simultaneously by making use of the periodicity and the quasi-stationarity of the problem. The ideal MHD equations have been extended in order to account for the effects of Europa's neutral atmosphere and the internal periodic induced magnetic fields on the plasma interaction. At the beginning of this work, Galileo magnetometer data acquired on four passes by Europa were used to investigate whether a fixed permanent dipole moment is present in the interior of the moon in addition to the induced dipole moment previously identified. We thereby confirm the presence of an inductive response and find that the dipole coefficients of the constant intrinsic field contribute at best in a very minor way to the magnetic field. The induced magnetic fields caused by the time variable plasma interaction are calculated in an interactive process. It is shown that the influence of these secondary induced magnetic fields is small compared to the induction caused by the time-varying background field. In addition, the influence of the induction on the plasma interaction is being studied. It is shown that the Alfven current system is deformed and displaced due to the induced magnetic fields. Furthermore, the plasma wake of Europa is deformed due to the induction. The resulting structure of Europa's plasma wake could explain why Galileo measurements did not detect high plasma densities along the E4 trajectory. By comparing the simulation results to the Galileo spacecraft measurements of three passes by Europa, we place the so far strongest constraints on the conductivity and the thickness of Europa's subsurface ocean. We find for the conductivity of Europa's ocean values of 500 mS/m or larger to be most suitable to explain the magnetic flyby data. If the ocean conductivity is less than 1 S/m, we suggest that the internal ocean has to be thicker than 25 km. The magnetic field and the plasma density measured during the Galileo E4 flyby are reproduced fairly well in the simulation. For the agreement between the data and our model, we see no need for a deviation of the upstreaming plasma flow from the nominal corotation direction.
|Item Type: ||Thesis (PhD thesis)|
|Subjects: ||Earth sciences|
|Uncontrolled Keywords: |
|Europa , Jupiter , Induktion , Weltraumphysik , Plasmaphysik||German|
|Europa , Jupiter , induction , space physics , plasma interaction||English|
|Faculty: ||Mathematisch-Naturwissenschaftliche Fakultät|
|Divisions: ||Mathematisch-Naturwissenschaftliche Fakultät > Institut für Geophysik und Meteorologie|
|Date Type: ||Completion|
|Date of oral exam: ||30 May 2006|
|Full Text Status: ||Public|
|Date Deposited: ||20 Jul 2006 10:07|
|Neubauer, Fritz M.||Prof. Dr.|
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