Collaborative Research: Dynamic and Non-Force-Free Properties of Solar Active Regions and Subsequent Initiation of Flares

Solar flares and coronal mass ejections (CMEs) correspond to a sudden, major reconfiguration of the coronal magnetic field. It has been well known that the topology and evolution of Sun's magnetic fields are determining factors in providing energy storage and initiation for solar eruptions. Although magnetic instabilities, such as torus and kink, are known to be related to onset of solar flares, it is still unclear how flare initiation is related to non-force-freeness and certain evolving structures of photospheric magnetic fields. These include small-scale magnetic reconnections, which are also signified by pre-flare brightenings. The use of state-of-the-art observations from the 1.6-m Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO), plus advanced magnetohydrodynamical (MHD) modeling tools and analysis techniques for the extrapolation of coronal magnetic field of the Sun matured significantly in recent years. The main purpose of this 3-year collaborative project is to expand the frontiers of existing knowledge on the magnetic energy release process occurring during solar flares. The research outcome of this project is expected to contribute to the scientific preparation for the future high-resolution solar flare studies, as well as the development of data analysis tools for the DKIST. The research project addresses some key science questions related to solar flares, namely: the non-force-free properties of solar atmosphere prior to eruptions, and the role of small-scale magnetic reconnections in the initiation of solar flares. Studying flare-associated magnetic field evolution promises to reveal the underlying physical mechanism of solar eruptions, which are the physical drivers of space weather at the Sun. Furthermore, this collaborative project has a strong educational and student training component. It will support two post-doctoral researchers: one at the NJIT and the other at the UAH, and a PhD student at the UAH. The NJIT will play a key role in training graduate students and young researchers to be the future users of the DKIST. The data analysis and imaging processing tools can be used by many other areas of science and engineering. Both the NJIT and UAH have a very diverse student population. The project will advance the education of underrepresented students in both institutions. The team will conduct a comprehensive study of solar flares in order to achieve a fundamental physical understanding of the aforementioned flare-related magnetic field evolution. The study will combine vector magnetograms from HMI, the spectropolarimeter of Hinode, and the high-resolution, high-cadence vector magnetograms from the GST. The high-resolution observations are necessary as they can reveal the fine details of dynamic magnetic field structures around flaring sites. The non-force-free properties of Sun's Active Regions (ARs) near the photosphere become even more prominent under these high-resolution observations. Three complementary sets of existing vector magnetograph data will be analyzed by the project teams. The SDO/HMI provides full-disk vector magnetograms with a cadence of about 2 to 12 minutes, which enable the study of the large-scale magnetic field structure and evolution. The BBSO/GST achieves a high resolution in the order of 0.1" and a temporal cadence of 30 seconds, thus providing a unique data source for studying the flare core regions in great details. The Hinode/SP data are obtained at a low cadence, but they cover a rich archive of flares since 2006 and provide a quality check for more recent GST magnetograms. The project teams will carry out Non-Force-Free Field (NFFF) extrapolations based on combined HMI, Hinode, and GST data and compare them with the more mature Non-Linear Force-Free Field (NLFFF) modeling results. The NFFF extrapolation will reveal the Lorentz force distribution and evolution of flare productive ARs. Using extrapolated coronal fields as initial conditions from extrapolations, the teams will apply 3D data-constraint and data-driven MHD modeling to select events. Using observations, extrapolation, and MHD simulations, the project teams will determine the role of non-force-freeness and evolving magnetic fields in flare initiation and precursor brightening. As part of the modeling validation, observed flare ribbon motion and the post-flare magnetic restructuring will be compared with the MHD modeling results. The research and EPO agenda of this project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research. 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.