Collaborative Research: SHINE--Exploring Reconnection-Driven Solar Explosive Events in Different Regimes through Modeling and Observation

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Magnetic reconnection is the mechanism driving explosions on the Sun ranging from nanoflares, ultraviolet bursts, to inter-planetary sized coronal mass ejections. At the core of reconnection is a current sheet where magnetic energy is converted to plasma kinetic energy. This project investigates how plasmoid instabilities lead to reconnection and solar explosions. Magnetic reconnection is a primary driver of space weather and an important fundamental physical process important to space physics, fusion science, and astrophysics. The work supports research of mid-career and early career scientists, including graduate student support. The team will develop lectures to undergraduate students from under-represented groups through NASA’s Heliophysics Summer School.Recent theoretical analyses and numerical simulations predict that reconnection current sheets can spontaneously become unstable to the plasmoid instability. The plasmoid instability fractures the reconnecting current sheet into secondary current sheets, plasmoids, and flux ropes, facilitating the onset of fast reconnection. Depending on the collisionality and global system size in relation to kinetic scales, plasmoid-mediated re- connection can result in a variety of dynamical behaviors. Appropriately capturing critical properties of the dynamical behaviors is crucial for modeling explosive events. This project will develop a deeper understanding of the onset and saturation of plasmoid-mediated fast reconnection in various regimes through a concerted interdisciplinary effort of numerical simulation and solar observation. This is accomplished by: (1) Performing numerical simulations of solar explosive events including large-scale coronal mass ejections in the solar corona and ultraviolet burst events in the lower solar atmosphere. These events cover a broad range of length scales, plasma densities, and temperatures, corresponding to reconnection in different parameter regimes. Simulation results will be compared with observations. (2) Investigating the onset and saturation of fast reconnection in different parameter regimes. To establish a basic understanding of how various models behave in different regimes, the team will conduct 2D and 3D simulations of reconnection in a well-controlled current sheet using resistive magnetohydrodyamic (MHD), Hall MHD, and multi-moment multi-fluid codes to test how microscopic physics descriptions affect the onset and saturation of fast reconnection at large, observable scales.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.