Study of the Formation and Topology of Flux Transfer Events using Global Numerical Simulation

English Abstract:

We have analyzed a global magnetohydrodynamic (MHD) simulation of the magnetosphere to study the formation and magnetic topology of flux transfer events (FTEs) for reconnection during assumed interplanetary plasma and magnetic field conditions. All the interplanetary conditions have been kept constant during the simulation time. The interplanetary magnetic field (IMF) had a large southward-duskward component. The grid resolution at the subsolar magnetopause is sufficiently high to allow the formation of FTEs. We observe the spontaneous formation of FTEs under constant solar wind conditions and zero dipole tilt. Five FTEs with clear magnetic perturbations have been detected. The characteristics of these five FTEs are identified, among them, the beginning and end of their magnetic signature, sense of propagation, speed of propagation and time onset of their movement. The first, second and fourth FTEs travel northward, while the others two move southward. The bipolar B_N signature and the intensification of the core magnetic field (B_M) are presented in all FTEs. The sense of propagation is mainly northward-dawnward in the Northern Hemisphere and southward-duskward in the Southern Hemisphere, which is consistent with the orientation of flows for a southward-duskward IMF case. The cross section of the first FTE has been analyzed in terms of the projected magnetic field, thermal pressure and core magnetic field. The typical magnetic characteristics of a flux rope were found. However, the analysis of the magnetic topology reveals that this structure is not a typical flux rope. Instead it is formed by two interlinked flux tubes which together seem to present similar characteristics of a flux rope. The magnetic topology over the magnetopause was calculated to study the generation mechanism of this event. Flow vortices have been observed in every FTE event. The flow vortices bring together regions of different magnetic topologies, which drive subsequent processes of magnetic reconnection. This could be the cause of the increased complexity in the topology observed after the interlinked flux tubes occurrence.