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

太阳耀斑和日冕物质抛射(CME)驱动着太阳系中最强烈的扰动。这些事件是由日冕磁场中流动的电流中储存的磁能的突然释放所驱动的。关于这些洋流的基本问题仍然存在：日冕洋流是如何演变成不稳定的，从而导致这样的事件发生？在耀斑和日冕物质抛射期间，这些电流是如何演变以释放磁能的？该项目通过对日冕极端紫外线(EUV)图像的建模和分析来解决这些问题。更广泛的影响包括对本科生的指导以及美国和澳大利亚机构之间的合作。将对2023年10月和2024年4月的美国大日食进行宣传。该项目将使用高斯的分离方法--这种方法在地球和行星磁性方面有着悠久的传统--到太阳活动区(AR)的光球层矢量磁图(3分量磁场的2D图)。高斯方法的核心思想是，光球场可以毫不含糊地划分为三个不同的部分，每个部分都有自己的来源：光球层下方的电流、光球层上方的电流和通过光球层的电流。我们把日冕洋流引起的光球场称为这些洋流的“光球印记”。仅靠光球印记本身并不能完全揭示日冕流的本质。非线性无力场(NLFFF)外推法以前被用来研究日冕电流，但这些模型底部边界上的场通常表现出与磁图场的本质不一致。虽然这两种方法都有局限性，但将它们结合起来可以极大地提高我们对日冕电流的理解。因此，该项目将在易发生耀斑和CME的ARs的案例研究中利用这两种方法来研究日冕流的结构和发展。该团队将分析耀斑/日冕物质抛射前后光球印记和NLFFF模型的演化，以及平静时期的演化，以建立基线变化率。日冕EUV图像也将进行上下文研究。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.