In this thesis, the spacecraft potential measured by the EFW instrument on Cluster has been used to map the plasma density distribution of the magnetosphere. A relation between the spacecraft potential and the plasma density has been established and three years of data have been binned to obtain a 3D image of the density distribution. Boundaries like the bow shock, the magnetopause, the plasmapause and the plasma sheet boundary layer (PSBL) are identifiable in this image.
The identification of the PSBL has been used to determine plasma sheet thicknesses. By assuming that the plasma sheet is symmetric about the neutral sheet and that the sheet position is known, the half thickness has been estimated for each PSBL crossing. A simplified method based on the dipole tilt angle has been used to determine the neutral sheet position relative to the GSM x-axis. On average the plasma sheet half thickness was found to be 4.73RE. There is, however a large spread in the data as the plasma sheet half thickness can take any values from 0RE to 12RE.
A statistical comparison of IMF Bz and the plasma sheet thickness has given a positive correlation of about 0.5 which indicates a trend as expected. However, the poor correlation against parameters like solar wind pressure and the energy input (epsilon parameter), and the large spread in data, may indicate that internal processes of the magnetosphere may govern the tail dynamics/reconnection. More work is needed to make this conclusive.