A Numerical Investigation Into The Dynamics Of Oscillatory Reconnection

Abstract

Magnetic reconnection is a fundamental plasma process that is at the heart of a plethora of dynamical events such as solar flares and coronal mass ejections. Theoretical models of reconnection however lack the time-dependent nature of such events as they are typically steady-state models. In recent years, due to increased observations of such dynamical events, an appreciation for the need for time-dependent models of reconnection has arisen. One such time-dependent model is that of oscillatory reconnection.
Oscillatory reconnection is a time-dependent, wave generating form of magnetic reconnection that is believed to be the origin for a number of dynamical events within the solar atmosphere such as quasiperiodic pulsations and solar jets. In this thesis, the dynamics of the oscillatory reconnection mechanism is investigated through the use of resistive magnetohydrodynamic (MHD) simulations.
A study into how the level of resistivity affects the oscillatory reconnection mechanism is carried out, finding that the periodicity of the system is independent of the resistivity. Conversely, it is found to have a direct effect on the amplitude of currents produced in the system and in turn the levels of ohmic heating. Additionally, it is also found to have a direct effect on the decay rate, acting to increase the damping rate when levels of resistivity are increased.
Results are also presented for an investigation into the dynamics of the mechanism. Identification of the MHD shocks that form within the mechanism is done finding good agreement with steady-state reconnection models in the literature. Additionally, initial results of an investigation into the energetics of the system are presented. The formation of diamond-like structures in the reconnection outflows are also reported on for the first time, with their similarity to Mach diamonds that form in supersonic jet exhausts discussed.
Finally, results are presented of a preliminary investigation into how a magnetic null point is impacted asymmetrically by a nonlinear fast magnetoacoustic wave. It is shown that the nonlinear propagation of such waves differs drastically from that of the linear case with the formation of a plethora of asymmetries. This result develops the mechanism beyond that of the generally used symmetric driving of the oscillatory reconnection mechanism.

Date of Award	27 Nov 2025
Original language	English
Awarding Institution	Northumbria University
Supervisor	James McLaughlin (Supervisor) & Gert Botha (Supervisor)