UCLA

Magnetic reconnection, a process characterized by the mixing of distinct magnetic flux tubes within a magnetized plasma, results in the exchange of energy between the electromagnetic fields of these flux tubes and the confined plasma. This phenomenon is observed across various astrophysical entities, playing a pivotal role in the energization and global transport of plasma. On Earth, magnetic reconnection is integral to the dynamics of the magnetotail, facilitating the depressurization of the tail during earthward convection, markedly elevating the temperature of magnetotail plasma, and generating field-aligned particle beams that pro- mote wave generation and growth. Observations across the magnetotail and under varying levels of geomagnetic activity have demonstrated magnetic reconnection’s importance and prevalence. It significantly influences global magnetospheric plasma energy transport during both quiescent and active periods through episodic magnetic reconnection events that pro- pel heated plasma ejecta in both earthward and tailward directions. Given its central role in global plasma transport and energization within the magnetotail this Ph.D. thesis seeks to elucidate key aspects of magnetotail reconnection to enhance our understanding of the magnetotail’s evolution.

Investigating the dynamics of magnetotail reconnection presents a multifaceted challenge. This Ph.D. thesis leverages ongoing inner-magnetosphere missions and advanced magnetic field models to dissect three critical aspects of this issue. 1) Assess whether global plasma convection during geomagnetic storms is influenced by intermittent or quasi-continuous mag- netotail reconnection. While prior studies have primarily concentrated on relatively quiet conditions, revealing two distinct plasma transport modes in the magnetotail—substorms characterized by irregular reconnection at approximately 25-30 Earth radii (RE) and steady magnetospheric convection featuring more consistent reconnection beyond 40 RE —a detailed investigation during intense storm conditions is notably absent. This analysis aims to cate- gorize magnetotail reconnection during storms as either intermittent or continuous, offering significant insights into energy transport mechanisms under such conditions. 2) Examine the frequency and impact of near-Earth magnetotail reconnection during storms, a phenomenon less understood compared to non-storm conditions traditionally located beyond 25 RE. With the recent solar cycle prompting more frequent storms, emerging evidence supports the oc- currence of very-near-Earth reconnection (VNERX). This study explores VNERX events and their contribution to storm dynamics. 3) Study the heating processes that take place during magnetotail reconnection. Simulations and observations show that most of the par- ticle energy gained through reconnection is in the form of thermal energy. In the near-Earth tail, gradients in plasma pressure can transfer the kinetic energy from reconnection ejecta into plasma heat far away from the x-line. However, in the mid-tail, where reconnection occurs most frequently, these gradients are diminished. We study whether particle heating is still significant in magnetotail reconnection at these distances, and what factors control that heating. The heating process of mid-tail reconnection has important implications towards understanding the thermal profile of the plasma sheet, a major source of plasma for the inner magnetosphere and the storm-associated ring current.