Venus plasma environmentThe : a comparison of Venus Express ASPERA-4 measurements with 3D hybrid simulations

Abstract

The thesis deals with the investigation of the plasma environment of Venus using data of the ASPERA-4 (Analyzer of Space Plasmas and Energetic Atoms) experiment onboard the Venus Express (VEX) spacecraft as well as a 3D hybrid code in order to study the solar wind-atmosphere interaction of an unmagnetized planet. By using data from the ion and electron spectrometers, the shapes and average locations of the plasma boundaries around the planet are determined. Additionally, the variation of the terminator bow shock position is analyzed as a function of the solar wind dynamic pressure and solar EUV flux. It is demonstrated that the shock location is insensitive to the upstream ram pressure and that the changes in the solar EUV radiation are too small over the period of the VEX observations to analyze solar activity dependence. The results of this data analysis and earlier studies are qualitatively compared with three-dimensional hybrid simulations which are based on VEX observations during low solar activity. But also simulations with PVO input parameters typical for solar maximum conditions are performed and compared with the VEX simulation results. The main focus of this study is the comparison of the plasma and magnetic field measurements provided by VEX with the results of three-dimensional hybrid simulations. The hybrid model is able to produce an adequate picture of the global plasma dynamics and processes at Venus. The positions of the plasma boundaries are well reproduced by the model and the simulated parameters are in fairly good agreement with the values measured by the ASPERA-4 and Magnetometer instruments.