The magneto-convective nature of dark striations and moving bright grains at the edge of pores

¹ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077, Göttingen, Germany
² Thüringer Landessternwarte, Sternwarte 5, 07778, Tautenburg, Germany
³ Big Bear Solar Observatory, New Jersey Institute of Technology, 40386 North Shore Lane, Big Bear City, CA, 92314, USA
⁴ Center for Solar-Terrestrial Research, New Jersey Institute of Technology, Newark, 07102-1982, NJ, USA
⁵ Astronomy Program, Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
⁶ Korea Astronomy and Space Science Institute, 776 Daedeok-daero, Yuseong-gu, Daejeon, 34055, Republic of Korea

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 January 2026
Accepted: 28 February 2026

Abstract

Context. High-resolution observations of the Sun reveal a multitude of small-scale striations throughout the photosphere. While these features are well observed in broad-band intensity images, spectropolarimetric observations remain rare.

Aims. In this study, we characterize small dark striations at the pore-granulation boundary and bright grains moving along them. We seek to describe their magneto-convective nature.

Methods. We analyzed restored context images and many-line Stokes inversions of a restored spectropolarimetric scan from GST/FISS-SP with a spatial resolution of 0.068″. In the inversion, we used 85 solar absorption lines within a 33 Å wide spectral window in the 5250 Å region. We compare the observations with a MURaM simulation to discern the magneto-convective nature of striations and grains.

Results. We find multiple dark striations in the vicinity of pores or active region intergranular lanes with a typical width of 0.09″ and moving bright grains that migrate along some of those striations toward the adjacent pore. Grains forming in a high-resolution MURaM simulation of a pore show similar lifetimes of about 70 s. A comparison of the atmospheric configurations of simulated and observed grains reveals good qualitative agreement in structure, dynamics, thermal, and magnetic stratification. The simulation shows that the dark striations form at the top of a convective plume confined by the surrounding field, and that their dark appearance is caused by plasma trapped in the field cusp at optical depth unity. The moving bright grains are composed of hot plasma pulled upwards by turbulent flows at the tip of the striation.

Conclusions. By combining high resolution spectro-polarimetry, many-line inversions, and MURaM simulations, we present the first analysis of the 3D fine structure of small-scale striations and moving bright grains in the vicinity of a pore and describe their magneto-convective nature.