Spatial distributions of extreme-ultraviolet brightenings in the quiet Sun

¹ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
² Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA, United States
³ Bay Area Environmental Research Institute, Moffett Field, CA, United States
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 ETH-Zurich, Wolfgang-Pauli-Str. 27, 8093 Zurich, Switzerland
⁷ Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, 7260 Davos Dorf, Switzerland
⁸ School of Physical Sciences, Dublin City University, Glasnevin Campus, Dublin D09 V209, Ireland
⁹ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
¹⁰ UCL-Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
¹¹ Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Ringlaan -3- Av, Circulaire, 1180 Brussels, Belgium
¹² Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119992 Moscow, Russia

^⋆ Corresponding author; chris.nelson@esa.int

Received: 12 May 2023
Accepted: 1 November 2024

Abstract

Context. The identification of large numbers of localised transient extreme ultraviolet (EUV) brightenings, on very small spatial scales, in the quiet Sun corona has been one of the key early results from Solar Orbiter. However, there are still a great deal of unknowns about these events.

Aims. In this work, we aim to better understand EUV brightenings by investigating their spatial distributions. Specifically, we have investigated whether they occur co-spatially with specific line-of-sight (LoS) magnetic field topologies in the photospheric network.

Methods. We detected the EUV brightenings in this work using an automated algorithm applied to a high-cadence (3 s) dataset sampled over ∼30 minutes on 8 March 2022 by the Extreme Ultraviolet Imager’s 17.4 nm EUV High Resolution Imager (HRI_EUV). Data from the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager (SDO/HMI) and Atmospheric Imaging Assembly (SDO/AIA) were used to provide context on the LoS magnetic field and for alignment purposes, respectively.

Results. We found a total of 5064 EUV brightenings within this dataset that are directly comparable to events reported previously in the literature. These events occurred within around 0.015–0.020% of pixels for any given frame. We compared eight different thresholds to split the EUV brightenings into four different categories related to the LoS magnetic field. Using our preferred threshold, we found that 627 EUV brightenings (12.4%) occurred co-spatially with strong bipolar configurations and 967 EUV brightenings (19.1%) occurred in weak field regions. Fewer than 10% of EUV brightenings occurred co-spatially with the unipolar LoS magnetic field, no matter what threshold was used. Of the 627 strong bipolar EUV Brightenings, 54 were found to occur co-spatially with cancellation, whilst 57 occurred co-spatially with emergence.

Conclusions. EUV brightenings are primarily found to occur co-spatially with the strong LoS magnetic field in the photospheric network. However, they do not predominantly occur co-spatially with (cancelling) bi-poles.