GEM: Kinetic structure and formation of pre-reconnection magnetotail thin current sheets

Understanding how energy is stored and explosively released in near-Earth space is critical to protecting modern technologies that depend on satellites, power grids, and communications systems. This project investigates the formation of thin current sheets (TCS), which are narrow regions of intense electrical current observed in Earth’s magnetotail during the quiet buildup phase of geomagnetic substorms. These substorms can lead to space weather disturbances that affect both space-based and ground-based systems. TCSs are thought to be a prerequisite for magnetic reconnection, the explosive process that triggers substorms, but their formation remains poorly understood. This research aims to clarify how specific ion behaviors—particularly when ions have directional energy preferences, or anisotropy—support the development of these thin structures. The project also supports the national interest by advancing scientific knowledge of geospace dynamics, which is essential for forecasting space weather. Additionally, it provides training for undergraduate students and offers early-career development opportunities for the principal investigator. The project uses state-of-the-art Particle-In-Cell (PIC) simulations to explore how ion anisotropy arises and enables the formation of thin current sheets in the magnetotail. Two central science questions guide the research: (1) What role does a realistic driving electric field play in generating ion anisotropy and enabling TCS formation? (2) What impact do anisotropic ions—originating outside the central current sheet—have on transforming a broader current layer into a TCS, either with or without an external driving field? The simulations incorporate novel, data-driven boundary conditions, including electric fields derived from data-mined magnetospheric reconstructions and ion populations informed by satellite observations. These include cold, anisotropic ions likely originating from Earth’s ionosphere and high-energy beams from magnetic reconnection exhausts. By resolving the physics behind TCS formation, this research will enhance scientific understanding of the substorm growth phase and energy release processes in space plasmas. The findings will have broader applications to other plasma environments, such as the solar wind and magnetospheres of other planets. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.