Date of Award
2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Space Science
Committee Chair
Qiang Hu
Committee Member
Haihong Che
Committee Member
Gang Li
Committee Member
Nikolai Pogorelov
Committee Member
Alphonse Sterling
Research Advisor
Qiang Hu
Subject(s)
Solar flares--Measurement, Solar magnetic fields, Sun--Corona
Abstract
Solar eruptions are manifestations of strong solar activities which occur in multiple scales and vary significantly in observations. It has also been increasingly realized that some scenarios initially proposed for relatively large-scale eruptions may persist down to much smaller/finer scales, largely owing to increasingly high-resolution observations of the Sun. However, confirming the coherent magnetic structures on the Sun remains challenging due to the lack of direct coronal magnetic field measurement. This dissertation mainly focuses on the topological analysis of multi-scale magnetic structures embodied in different solar eruptions with available observations. It is achieved by reconstructing the 3D coronal magnetic field through one unique nonlinear force-free field (NLFFF) extrapolation method, the CESE-MHD-NLFFF code, modified and tested for nonuniform embedded magnetograms. The performance of the modified code is evaluated extensively through a series of test runs based on different input magnetograms and grid constructions. Two selected solar flare eruptions are investigated to make a connection between the magnetic flux ropes (MFRs) on the Sun and their interplanetary counterparts quantitatively. For event 1, a coherent MFR before the flare eruption is identified combining the multi-wavelength observations and the NLFFF extrapolation results. The total magnetic reconnection flux during the eruption amounts to ~ 1021 Mx, which is measured by analyzing the associated flare ribbons via remote-sensing observations. It is significantly larger than the flux in the identified pre-eruptive MFR (1019 ~ 1020 Mx). For event 2, there is no pre-eruptive MFR found with the same criteria as event 1. In both events, the total magnetic reconnection flux (in the order of ~1021 Mx) agrees with the corresponding magnetic flux contents of the MFRs after the eruptions from the in situ modeling results. To study the fine-scale magnetic structures, the modified CESE-MHD-NLFFF code is applied to a flare precursor event with nonuniform embedded magnetograms from the Goode Solar Telescope (GST) and the Solar Dynamics Observatory (SDO). By comparing the extrapolation results with the simultaneous SDO and high-resolution GST observations, the magnetic field lines originating from the precursor brightening regions show a more consistent configuration with observations. The resolved fine-scale magnetic structures exhibit low-lying sheared arcades characteristic of a plausible configuration for precursor magnetic reconnection before the main flare onset. In addition, a recurrent solar jet event is also studied by employing two sets of embedded magnetograms from GST and SDO. We find small closed loops surrounded by open field lines in two runs, which indicates a scenario of interchange reconnection leading to the occurrence of the jets. These quantitative investigations contribute to understanding the important role of magnetic reconnection in shaping the topological features seen in observations and shed light on the underlying physical mechanisms driving the solar eruptions.
Recommended Citation
He, Wen, "Coronal magnetic field extrapolation and topological analysis of multi-scale magnetic structures for solar eruptions" (2024). Dissertations. 399.
https://louis.uah.edu/uah-dissertations/399