Coronal dimmings from active region 13664 during the May 2024 solar energetic events

¹ University of Graz, Institute of Physics, Universitätsplatz 5, 8010 Graz, Austria
² University of Graz, Kanzelhöhe Observatory for Solar and Environmental Research, Kanzelhöhe 19, 9521 Treffen, Austria
³ NorthWest Research Associates, 3380 Mitchell Lane, Boulder, CO 80301, USA
⁴ Skolkovo Institute of Science and Technology, Bolshoy Boulevard 30, bld. 1, 121205 Moscow, Russia

^⋆ Corresponding author: amaia.razquin-lizarraga@uni-graz.at

Received: 26 March 2025
Accepted: 13 May 2025

Abstract

Context. Coronal dimmings are regions of transiently reduced brightness in extreme ultraviolet (EUV) and soft X-ray (SXR) emissions associated with coronal mass ejections (CMEs), providing key insights into CME initiation and early evolution. During May 2024, AR 13664 was among the most flare-productive regions in recent decades, generating 55 M-class and 12 X-class flares along with multiple Earth-directed CMEs. The rapid succession of these CMEs triggered the most intense geomagnetic storm in two decades.

Aims. We study coronal dimmings from a single active region (AR 13664) and compare them with statistical dimming properties. We investigate how coronal dimming parameters – such as area, brightness, and magnetic flux – relate to key flare and CME properties.

Methods. We performed coronal dimming detection on observations from the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory (SDO). We used a logarithmic base-ratio thresholding technique to identify dimming regions, selecting pixels where log(I/I₀) ≤ −0.19. Due to the high activity of the AR, we propose a quantitative threshold for distinguishing real mass depletion dimmings from unrelated intensity reductions by setting a threshold on the dimming area reached within the first hour (A ≥ 6.48 × 10⁹ km²). We systematically identified all flares ≥M1.0, all coronal dimmings and all CMEs (from the CDAW SOHO/LASCO catalogue) produced by AR 13664 during 2024 May 1–15, and studied the associations between the different phenomena and their characteristic parameters.

Results. We detect coronal dimmings in 22 events, with 16 occurring on-disc and six off-limb. Approximately 83% of X-class flares and 23% of M-class flares are associated with CMEs, with 13 out of 16 on-disc dimmings linked to CME activity. The dimmings in AR 13664 exhibit total unsigned magnetic fluxes exceeding 5.5 × 10²¹ Mx, reflecting the region’s high magnetic flux density; and dimming areas greater than 1.16 × 10¹⁰ km². Previous statistical studies had shown a correlation between dimming parameters and flare parameters. We find that dimming parameters for the May 2024 events, particularly total dimming area and area growth rate, have a stronger correlation with GOES soft X-ray peak flux and fluence than anticipated, highlighting the connection between energy release in flares and the accompanying dimming. We find correlations between dimming properties and CME maximum velocities, which indicate that coronal dimmings serve as proxies for CME speeds.

Conclusions. Our results support the strong interplay between coronal dimmings and flares, as we find increased correlations between flare and dimming parameters in this single-AR study compared to the general dimming population. Furthermore, we confirm that coronagraphic observations, unable to observe the lower corona, underestimate correlations between CME velocities and dimming parameters, as they fail to capture the early CME acceleration phase. This highlights the critical role of dimming observations in providing a more comprehensive understanding of CME dynamics.