Active chromospheric fibril singularity

Coordinated observations from Solar Orbiter, SST, and IRIS

¹ Rosseland Centre for Solar Physics, University of Oslo P.O. Box 1029 Blindern N-0315 Oslo, Norway
² Institute of Theoretical Astrophysics, University of Oslo P.O. Box 1029 Blindern N-0315 Oslo, Norway
³ NASA Goddard Space Flight Center, Heliophysics Science Division Greenbelt MD 20771, USA
⁴ Department of Physics and Astronomy, George Mason University Fairfax VA 22030, USA
⁵ Sorbonne Université, Observatoire de Paris – PSL, École Polytechnique, Institut Polytechnique de Paris, CNRS, Laboratoire de physique des plasmas (LPP) 4 Place Jussieu F-75005 Paris, France
⁶ Institute for Solar Physics, Dept. of Astronomy, Stockholm University, Albanova University Center 10691 Stockholm, Sweden
⁷ Statkraft AS Lysaker, Norway
⁸ Instituto de Astrofísica de Canarias E-38205 La Laguna Tenerife, Spain
⁹ Universidad de La Laguna, Dept. Astrofísica E-38206 La Laguna Tenerife, Spain
¹⁰ Max-Planck-Institut für Sonnensystemforschung Justus-von-Liebig-Weg 3 37077 Göttingen, Germany

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

Received: 30 July 2025
Accepted: 30 November 2025

Abstract

Context. The fine structures of the solar chromosphere, driven by photospheric motions, play a crucial role in the dynamics of solar magnetic fields. Many such structures have already been identified, such as fibrils, filament feet, and arch filament systems. Nevertheless, high-resolution observations show a wealth of structures whose nature remains elusive.

Aims. We observed a puzzling, unprecedented chromospheric fibril singularity in the close vicinity of a blow-out solar jet and a flaring loop. We aim to understand the magnetic nature of this singularity and the cause of its activity using coordinated high-resolution, multi-wavelength observations.

Methods. We aligned datasets from Solar Orbiter, SST, IRIS, and SDO. We re-projected the Solar Orbiter datasets to match the perspective of the Earth-based instruments and performed potential field extrapolations from Solar Orbiter/PHI data. We analysed the spatial and temporal evolution of the plasma structures and their link with the surface magnetic field. This led us to derive a model and scenario for the observed structures, which we explain in a general schematic representation.

Results. We have discovered a new feature: a singularity in the chromospheric fibril pattern. It forms in a weak magnetic-field corridor between two flux concentrations of equal sign, at the base of a vertically inverted-Y-shaped field-line pattern. In this specific case, some activity develops along the structure: first, a flaring loop at one end, and second, a blow-out jet at the other end, where a coronal null point was present and associated with a chromospheric saddle point located on the fibril singularity. The observations suggest that both active phenomena are initiated by converging photospheric moat flows that exert pressure on this fibril singularity.