The Interaction of Neptune with the Solar Wind
Abstract
The low-energy plasma and magnetic field-data obtained by Voyager 2 in the subsolar interaction regions of Neptune is analyzed and discussed in this thesis. Theoretical models which may account for the observed phenomena are proposed. As the supersonic solar wind approaches the magnetic obstacle of Neptune, it cannot smoothly flow around the magnetosphere of the planet, but forms a magnetohydrodynamic (MHD) shock, the bow shock. To enhance the analysis of the bow shock, the non-linear least squares, MHD jump conditions fitting technique of Vinas and Scudder (1986) is extended to include plasma temperature observations in the form of the conservation of the normal momentum flux and energy density flux. The improved analysis technique reveals that the nearly subsolar Neptunian bow shock is a low beta, high Mach number, quasi-perpendicular strong shock slowly moving away from the planet toward the Sun. Also, the shock microstructure features are resolved and presented. After crossing the bow shock, the now subsonic and heated solar wind plasma passes through the turbulent magnetosheath before reaching the boundary of the planet's magnetosphere, the magnetopause (MP). The observed magnetofluid parameters in the inbound sheath are well modeled by a simple gas dynamic simulation with convected magnetic fields. Significant discrepancies are observed by Voyager 2 only near the MP crossing. Because of the relatively large tilt angle of the Neptunian magnetic dipole axis from the planet's rotation axis, the southern magnetic polar regions face into the solar wind flow for a short period of time in every planetary rotation. Voyager 2 had the good fortune to encounter Neptune's MP at such a configuration. To analyze this unusually positioned planetary MP, the traditional magnetic variance analysis is supplemented by a newly developed MHD rotational discontinuity fitting method. The magnetic variance and MHD techniques, however, yield widely different results for the orientation of the MP surface normal. Finally, the observed sheath plasma in the upper regions of the Neptunian magnetosphere is shown to form a layer similar in characteristics to the Earth's entry layer. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened by UMI.).
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1993
- Bibcode:
- 1993PhDT........84S
- Keywords:
-
- VOYAGER 2;
- Physics: Astronomy and Astrophysics, Physics: Fluid and Plasma, Physics: Atmospheric Science