THE EFFECTS OF THE INTERACTION OF A FULLY IONIZED PLASMA WITH WEAKLY MAGNETIZED PLANETARY OBSTACLES.

摘要

In this thesis several problems in solar system plasma physics are examined. The problems chosen deal with the dynamics of the interaction of a fully ionized plasma with planetary obstacles in the solar system. In particular, problems on the solar wind interaction with Venus and the interaction of the Jovian magnetosphere with the (icy) Galilean satellites are addressed. The thesis is divided into three Chapters. In Chapter I the nature of the solar wind interaction with Venus is examined. This chapter is divided into three parts. The first part is a theoretical model of the large scale dynamics and structural variability of the Venus ionosphere. Theoretical modelling of the effect of the variability of the solar wind dynamic pressure on the structure of the ionosphere is compared with observations from Mariner 5,10, Venera 9,10 and Pioneer Venus. The second part of Chapter I is on the onset and development of Kelvin-Helmholtz instability at the Venusionopause. Finite larmor radius corrections to the MHD equations are taken into account in deriving the conditions for the onset of Kelvin-Helmholtz instability. A maximum growth rate of the instability is shown to occur at a short wavelength cutoff which is dependent upon the ion Larmor radius and the flow velocity upstream of the ionopause as well as the density gradient across that surface. Models for the nonlinear evolution of Kelvin-Helmholtz instability indicate the formation of "magnetic flux ropes" in the Venus ionosphere as well as mass loading of the solar wind by atmospheric ions. These predictions are compared with Pioneer Venus observations. Part 3 of this chapter deals with the generation of plasma instabilities by mass loading of the solar wind. Starting with the Vlasov equation, dispersion relations are derived and solutions obtained over a complete range of frequencies and wavelengths for electromagnetic modes propagating parallel to the (ambient) interplanetary magnetic field. In Chapter II the interaction of the Jovian magnetosphere with the icy Galilean satellites, Europa, Ganymede and Callisto is studied. Models of atmospheres and ionospheres of the satellites are developed for a variety of possible volatiles and the effects of the interaction of the Jovian magnetosphere with both the model atmospheres and possible satellite magnetic fields are examined. Plasma and micrometeoroid bombardment of the satellite surfaces are considered as a possible explanation of the asymmetry in the brightness albedos and spectral reflectances of the satellites. In Chapter III the hydrodynamic modal equations are developed for the purpose of studying 3-dimensional planetary and stellar atmospheric dynamics. Each of the ordinary hydrodynamic variables is separated into a horizontal mean and fluctuating part, and the fluctuating part is expanded in a complete set of hexagonally symmetric orthonormal eigenfunctions in the horizontal plane. A series of ten modal equations, in the mean and fluctuating pressure, density, velocity, and internal energy, is derived and applications to the dynamics of the Venus ionosphere and other atrophysical systems considered. Appendix A details the properties of the hexagonal planforms and illustrates some computer solutions for fluid flow in the hexagonal cells.