Automatic detection of small-scale EUV brightenings observed by the Solar Orbiter/EUI^⋆

¹ Department of Physics, Faculty of Science, University of Zanjan, University Blvd., Zanjan, 45371-38791 Zanjan, Iran
e-mail: safari@znu.ac.ir
² Observatory, Faculty of Science, University of Zanjan, University Blvd., Zanjan, 45371-38791 Zanjan, Iran
³ Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Ringlaan -3- Av. Circulaire, 1180 Brussels, Belgium
⁴ Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
⁵ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁶ Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle Upon Tyne NE1 8ST, UK
⁷ ETH-Zürich, Hönggerberg campus, HIT Building, Zürich, Switzerland
⁸ Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, 7260 Davos Dorf, Switzerland
⁹ RCAAM of the Academy of Athens, 4 Soranou Efesiou Street, 11527 Athens, Greece
¹⁰ UCL-Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
¹¹ Leibniz Institute for Astrophysics in Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹² Centre for mathematical Plasma Astrophysics, Mathematics Department, KU Leuven, Celestijnenlaan 200B bus 2400, 3001 Leuven, Belgium
¹³ Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
¹⁴ Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119992, Moscow, Russia

Received: 3 February 2022
Accepted: 1 April 2022

Abstract

Context. Accurate detections of frequent small-scale extreme ultraviolet (EUV) brightenings are essential to the investigation of the physical processes heating the corona.

Aims. We detected small-scale brightenings, termed campfires, using their morphological and intensity structures as observed in coronal EUV imaging observations for statistical analysis.

Methods. We applied a method based on Zernike moments and a support vector machine (SVM) classifier to automatically identify and track campfires observed by Solar Orbiter/Extreme Ultraviolet Imager (EUI) and Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA).

Results. This method detected 8678 campfires (with length scales between 400 km and 4000 km) from a sequence of 50 High Resolution EUV telescope (HRI_EUV) 174 Å images. From 21 near co-temporal AIA images covering the same field of view as EUI, we found 1131 campfires, 58% of which were also detected in HRI_EUV images. In contrast, about 16% of campfires recognized in HRI_EUV were detected by AIA. We obtain a campfire birthrate of 2 × 10⁻¹⁶ m⁻² s⁻¹. About 40% of campfires show a duration longer than 5 s, having been observed in at least two HRI_EUV images. We find that 27% of campfires were found in coronal bright points and the remaining 73% have occurred out of coronal bright points. We detected 23 EUI campfires with a duration greater than 245 s. We found that about 80% of campfires are formed at supergranular boundaries, and the features with the highest total intensities are generated at network junctions and intense H I Lyman-α emission regions observed by EUI/HRI_Lya. The probability distribution functions for the total intensity, peak intensity, and projected area of campfires follow a power law behavior with absolute indices between 2 and 3. This self-similar behavior is a possible signature of self-organization, or even self-organized criticality, in the campfire formation process.