Collaborative Research: SHINE--Using Photospheric Imprints of Coronal Currents to Understand Coronal Magnetic Structure

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Solar flares and coronal mass ejections (CMEs) drive the strongest disturbances in the solar system. These events are powered by the sudden release of magnetic energy stored in electric currents flowing in the coronal magnetic field. Basic questions about these currents remain: How do coronal currents evolve to become unstable in the lead up to such events? And how do these currents evolve to release magnetic energy during flares and CMEs? This project addresses these questions through modeling and analysis of coronal extreme ultra violet (EUV) images. The broader impacts include mentoring of undergraduate students and collaboration between US and Australian institutes. Outreach will be conducted for the Great American October 2023 and April 2024 solar eclipses. This project will employ Gauss’s separation method — which has a long heritage in terrestrial and planetary magnetism — to photospheric vector magnetograms (2D maps of the 3-component magnetic field) of solar active regions (ARs). The core idea of Gauss’s method is that the photospheric field can be unambiguously partitioned into three distinct parts, each with its own source: currents below the photosphere, currents above it, and currents passing through it. We refer to the part of the photospheric field due to coronal currents as the ”photospheric imprint” of these currents. Photospheric imprints, by themselves, cannot fully reveal the nature of coronal currents. Nonlinear, force-free field (NLFFF) extrapolations have previously been used to study coronal currents, but fields on these models’ bottom boundaries typically exhibit substantial inconsistencies with magnetogram fields. While both methods have limitations, combining them can substantially improve our under- standing of coronal currents. Accordingly, the project will exploit both approaches in case studies of flare- and CME-prone ARs, to investigate the structure and development of coronal currents. The team will analyze evolution in photospheric imprints and NLFFF models before and after flares/CMEs, and in quiet epochs to establish baseline rates of change. Coronal EUV images will also be studied for context.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.