Three-dimensional multispecies global MHD studies of the solar wind interaction with Mars and Saturn's magnetospheric plasma flow with Titan.

Abstract

This dissertation presents numerical simulation results of the interaction of the solar wind/magnetospheric plasma flow with weakly magnetized/unmagnetized solar system bodies (Mars and Titan) using a multi-species global MHD model. Mars and Titan are both considered as being weakly magnetized/non-magnetized bodies with well-extended atmospheres. Therefore, the solar wind/magnetospheric plasma flow interacts with the corresponding ionosphere/atmosphere systems directly. A 2nd-order Godunov-type, finite-volume, upwind method is used to solve the multi-species MHD equations. The study of the solar wind interaction with Mars started with a three-species MHD model with Cartesian coordinate grid system, which considered protons in the solar wind and the two dominant heavy ions (O₂<super> +</super> and O<super>+</super>) in the ionosphere, separately. More extensive studies are carried out by using an updated 4-species MHD model with a spherical coordinate grid system, which gives a very good altitude resolution and a more realistic ionosphere. The model results are consistent with the Viking observations of the ionospheric ion density and the MGS measured bow shock locations. Using this updated model, we also study the effects of crustal magnetic field, solar radiation, magnetic field orientation, charge exchange and impact ionization. A three-dimensional 7-species MHD model is used to study the interaction of Titan's ionosphere and Saturn's magnetosphere. The spherical grid system is used in the calculations to get a good resolution in the ionospheric region. The simulation results have been compared with past Voyager measurements and observations of the first three flybys (Ta, Tb and T5) of Titan by Cassini, which agree reasonably well with the observations. The major advantages of the multi-species MHD models are as follows. The use of separate ionospheric and solar wind/magnetospheric constituents allows us to evaluate the mass loading process more accurately. The multi-species approach also allows us to establish how the solar wind/magnetospheric flow affects the ionospheric flow and structure and vice versa. The multi-species MHD models also enable us to determine the density distributions of the major ion species in the interaction region especially in the ionosphere. Although some kinetic effects such as that due to finite gyroradius effects, are neglected in the current MHD model, it still successful in describing the overall picture, including some of the most important features, which are consistent with observations.