Evidence of suppressed nonthermal broadening in a flare ribbon from stereoscopic observations
Year: 2026
Type: article
Abstract: Flare ribbons are footpoints of newly reconnected magnetic loops. They are commonly associated with strong plasma flows and a pronounced nonthermal broadening of transition-region lines resulting from impulsive energy deposition. However, the mechanism governing energy transport into flare ribbons remains uncertain, particularly under different magnetic field configurations. We aim to understand the energy deposition process at a flare ribbon located close to a sunspot by determining the physical nature of the small‑scale downflows hosted by the ribbon. We studied small-scale downflows in a remote ribbon during the M7.7-class event on 30 September 2024 using coordinated observations from the Solar Dynamics Observatory, the Interface Region Imaging Spectrograph (IRIS), and Solar Orbiter. We used stereoscopic imaging from Solar Orbiter and IRIS to detect plane-of-sky motions on small scales (∼200,km). We conducted spectroscopic analysis of IRIS Si iv profiles complemented by C ii and Mg ii diagnostics. -1 $, while IRIS images (disk view) reveal plane-of-sky speeds of 70--85,km,s^-1. In contrast, the IRIS Si iv profiles at the brightest ribbon pixels are well approximated by a single Gaussian, with minimal Doppler shifts and unexpectedly small nonthermal widths (∼10,km,s,$^ -1 ). Peak Si iv emission also coincides with a deeper Mg ii central reversal, while the electron densities are one to two orders of magnitude higher than typical quiet-Sun values. The absence of significant line-of-sight velocity and nonthermal broadening differs from the typical behavior of flare ribbons. Our results are consistent with a scenario in which plasma motions are guided by highly inclined (nearly horizontal) magnetic fields in a chromospheric canopy and are not accompanied by strong turbulence or wave motions. This study suggests that flare ribbons can exhibit a wide diversity of lower-atmospheric responses and emphasizes the critical role of magnetic field geometry.
Source: Astronomy and Astrophysics
Authors: Ziwen Huang, L. P. Chitta, L. Teriaca
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: Bundesministerium für Wirtschaft und Klimaschutz, National Aeronautics and Space Administration, UK Space Agency, European Commission, Belgian Federal Science Policy Office, Centre National d’Etudes Spatiales, Deutsches Zentrum für Luft- und Raumfahrt, Bundesministerium für Wirtschaft und Energie, Ames Research Center, HORIZON EUROPE Framework Programme, European Research Council
OpenAlex ID: W7222206115