Magnetic flux systems involved in the May 2024 solar energetic events from AR 13664 inferred through coronal dimmings

¹ University of Graz, Institute of Physics, Universitätsplatz 5, 8010 Graz, Austria
² NorthWest Research Associates, 3380 Mitchell Lane, Boulder, CO 80301, USA
³ University of Graz, Kanzelhöhe Observatory for Solar and Environmental Research, Kanzelhöhe 19, 9521 Treffen, Austria

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

Received: 26 January 2026
Accepted: 18 March 2026

Abstract

Context. Coronal dimmings are transient depletions of coronal plasma observed in extreme ultraviolet and soft X-ray wavelengths interpreted as low-corona signatures of coronal mass ejections (CMEs). Their evolution is closely linked to CME dynamics, flare reconnection, and the large-scale reconfiguration of the coronal magnetic field. During May 2024, the active region (AR) 13664 produced 66 ≥M-class flares alongside a sequence of fast CMEs that caused the largest geomagnetic storm since 2003. AR 13664 was also among the largest active regions and contained one of the largest amounts of magnetic flux ever recorded. It provided an exceptional opportunity to study the magnetic coupling between dimmings, flares, and CMEs within a single highly active AR.

Aims. We investigate the morphology, magnetic properties, and temporal evolution of coronal dimmings produced by AR 13664. We expand on a previous paper where we identified all coronal dimmings from AR 13664 and performed a statistical analysis of their characteristic parameters in relation to the associated flares and CMEs to determine how the spatial development of the dimmings relates to flare ribbon locations and to the magnetic field configuration of the AR. We aim to identify the magnetic flux systems involved in the eruptions and assess how the observed dimming evolution reflects large-scale coronal restructuring and CME initiation.

Methods. We analysed 16 on-disc coronal dimmings from AR 13664 detected in SDO/AIA 211 Å observations between May 1 and 14, 2024. We extracted coronal dimmings using logarithmic base-ratio thresholding, and their magnetic properties were derived from SDO/HMI line-of-sight magnetograms. We detected flare ribbons in AIA 1600 Å data using an adaptive thresholding technique and computed their reconnection fluxes from radial magnetic field maps. To explore the magnetic environment, we used high-resolution potential field source surface (PFSS) and non-linear force-free (NLFF) extrapolations of the coronal magnetic field and traced the magnetic flux systems connecting dimming regions, flare ribbons, and coronal holes.

Results. We found strong correlations between flare ribbon and dimming parameters. The magnetic dimming area and flare ribbon area correlate with c = 0.65 ± 0.13, and the unsigned dimming and reconnection fluxes correlate with c = 0.60 ± 0.18, consistent with earlier statistical studies. The morphology of the dimmings changed systematically over the evolution of the AR, with southwards expanding dimmings occurring before May 9 and northwards expanding ones thereafter. This transition coincides with a change in the flare ribbon locations. AR 13664 contains two long, strong, and almost horizontal, i.e. east-west, polarity inversion lines (PILs), and the flare ribbon locations shift from the southern to the northern PIL. Together with the dimming location, these changes imply the presence of two distinct magnetic domains. The PFSS extrapolations showed that southward (northward) dimmings are mainly strapping flux dimmings with magnetic field lines vaulting above the southern (northern) PIL. The final extent of the dimmings was then given by the exterior flux involved in the eruption via stretching and reconnection. In one event, we found an extended quiet Sun dimming potentially triggered by field line opening due to the passage of an extreme ultraviolet wave.