2022/11/03 by Welsch, Brian T.
#FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2211.01911
Coronal electric currents store the magnetic energy that is released in solar flares and coronal mass ejections (CMEs). Here, we use photospheric vector magnetic field observations to study currents in active regions 10930 and 11158, which both produced eruptive, X-class flares. We employ Gauss's separation method in Cartesian geometry to partition the photospheric field into three distinct components: (i) the toroidal field, BT, from vertical currents, Jz, passing through the photosphere; (ii) B^<, from horizontal currents, Jh^<, flowing below it; and (iii) B^>, from horizontal currents, Jh^>, flowing above it. We refer to B^> as the photospheric imprint of coronal currents. We give two representations of B^< and B^>: (i) as second-order derivatives of poloidal potentials P^< and P^>, respectively; and (ii) in terms of gradients of interior and exterior scalar potentials, respectively. The central polarity inversion line (PIL) in each region possesses magnetic structure similar to that reported in AR 12673 by Schuck et al. (2022): (i) BT, which arises from Jz, produces sheared fields along the PIL; (ii) B^> exhibits large-scale, spatially coherent structure, consistent with Jh^> flowing above and along the PIL; and (iii) the near-PIL currents Jh^< and Jh^> are roughly parallel. Because parallel currents attract, such parallel-current configurations are likely more stable than misaligned-current configurations. Current Jh^> flowing along a PIL increases the magnitued of the gradient of Bz across the PIL, providing a physical explanation for previously reported empirical associations of strong, cross-PIL gradients in Bz with flare and CME occurrence.