Universität zu Köln

Backes, Heiko (2005). Titan's interaction with the Saturnian magnetospheric plasma. PhD thesis, Universität zu Köln.

Preview

PDF backes.pdf Download (6MB)

Abstract

An advanced 3D model for Titan s interaction with the Saturnian magnetospheric plasma has been developed. The ideal magnetohydrodynamic (MHD) equations have been extended in order to account for the effects of Titan s dense neutral atmosphere on the plasma interaction. The ion-neutral friction plays a key role in the deceleration of the magnetospheric plasma. The ionosphere is created from the neutral atmosphere by applying a 3D radiation model for the solar EUV radiation. Impact ionization rates by photoelectrons are calculated effectively. In order to include the process of impact ionization by magnetospheric electrons we have developed a time dependent flux tube model which accounts for flux tube motion through the atmosphere and electron heat conduction along the magnetic field lines. On Titan s nightside magnetospheric electron impact ionization is the only source for ion production. Thus, we obtain a 3D ionosphere that depends on the Saturnian local time (SLT) and the subsolar latitude (SSL). As a reference for the incident magnetospheric plasma the parameters derived from Voyager 1 measurements are used. The model is applied to three different cases that match the situations at the Cassini flybys TA, T5, and T34 at Titan. The results cover two fields, the ionosphere and the global plasma interaction. In the first part the resulting ionospheric properties are discussed. The peak electron density on the dayside is about an order of magnitude lower than on the nightside. The behavior of certain ionospheric regions and layers as a function of the angle to the ram direction and SLT are examined in the upstream hemisphere. The model produces a magnetic ionopause layer that separates the upper magnetized from the lower non- or weakly magnetized ionosphere. Its altitude varies between 500 km on the nightside and 1000 km on the dayside. We derive an empirical expression for the magnetic field magnitude at the magnetic barrier peak. Two different mechanisms for the generation of the magnetic barrier are discussed. The global plasma interaction is explained in terms of MHD waves. The super-Alfv´enic flow produces Alfv´en tubes. The primary interaction region, where the effect of the neutral gas on the plasma is above 1%, has a radius of 2.3 Titan radii. The major part of the magnetospheric plasma flows around a domain that consists of the primary interaction region and the volume where the nominal northern and southern Alfv´en tubes intersect each other in the tail. The deflected flow from the two flanks converges at about 4.5 Titan radii downstream from Titan s center. Plasma pick-up occurs basically at the flanks of Titan s atmosphere. In the tail region the increased plasma density is distributed along the magnetic field by a pressure gradient. We derive a total loss rate of 30 g/s independent of SLT. The plasma interaction generates an electric current system. The currents in the primary interaction region are split into their diamagnetic, inertial, and atmospheric contributions. The magnetic ionopause layer is associated with atmospheric currents. The upper boundary of the magnetic barrier corresponds to diamagnetic currents. Inertial currents appear in regions of plasma pick-up and accelerate the newly-created plasma. The currents in the primary interaction region are connected to the currents in the Alfv´en tubes. The net current along one half Alfv´en tube is about 3e4 A. For a comparison with the data from the first close Titan encounter of Cassini, we present the results from the model for TA along the trajectory. Our model predicts an inbound and outbound crossing of the magnetic ionopause layer.

Item Type:	Thesis (PhD thesis)
Translated title:	Title Language Wechselwirkung von Titan mit dem Plasma der Saturnmagnetosphäre German
Creators:	Creators Email ORCID ORCID Put Code Backes, Heiko backes@geo.uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-14075
Date:	2005
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:	Earth sciences
Uncontrolled Keywords:	Keywords Language Titan , Plasmawechselwirkung , Saturn , Magnetosphäre , Planetenphysik German Titan , plasma interaction , Saturn , magnetosphere , planetary physics English
Date of oral exam:	1 December 2004
Referee:	Name Academic Title Neubauer, Fritz M. Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/1407