Interplanetary Magnetic Field Influence on Flux Transfer Events at Mercury

Abstract

Reconnection between the interplanetary magnetic field (IMF) and Mercury’s intrinsic magnetospheric field at the dayside magnetopause drives the Dungey Cycle of magnetic flux. The formation of subsequent evolution of large magnetic structures known as flux transfer events (FTEs) therefore represents an important contribution to magnetospheric dynamics. This thesis presents three studies investigating the factors influencing the rate and location of FTEs, as well as the nature of their subsequent motion and evolution. Flux transfer events in the dayside magnetosphere of Mercury have been visually identified using 12 Mercury years of Magnetometer data from the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft, covering the period from March 2011 to February 2014. The dependence of the observation rate on the orientation of the IMF in the magnetosheath is investigated, showing a clear preference for FTE formation during periods of southward IMF, and therefore antiparallel reconnection. The locations of the FTE observations have also been analysed along with their direction of motion, in order to investigate the location and orientation of the average reconnection X-line for different IMF orientations. The motions are also used to produce a map showing the convection of the magnetic field in the dayside magnetosphere. Finally, differences in the magnetic field signatures of the observed FTEs with various parameters, including IMF strength and orientation, are probed through the use of superposed epoch analysis. The results provide evidence of FTE rotation with increased distance from the subsolar point, as well as compression of the leading edge of the structure as it moves through the surrounding magnetic field and plasma.