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Abstract The Detection and EUV Flare Tracking (DEFT) tool automatically identifies flare precursors in extreme ultraviolet (EUV) observations in a fast and consistent manner, with minimal computational overhead. DEFT currently uses GOES/SUVI 304 Å observations to detect, group, and flag sudden impulses that could be precursors to flares. In this study, we analyzed precursor signatures before 351 flares (150 C, 150 M, and 51 X class flares) that occurred from 2017 to date. Across these magnitudes, precursors were detected for 93% of the flares when using a 6 hr window before the flare start times. Using superposed epoch analysis, we found that elevated precursor activity tends to occur across all magnitude flares in the last 2 hr before the flares. The frequency of precursors gradually increases before M class flares but decreases for C class flares. We also found that in the last 20 minutes there is a significantly higher precursor frequency, pixel count, and power associated with M class flares than C class flares. We suggest that the observed EUV precursors are the observable signatures of small-scale magnetic reconnection events, and the consistently increasing frequency of precursor activity could indicate that the region is becoming increasingly unstable and reaching a critical stage that could result in flare initiation. Continuing research on EUV precursors is essential to better understand preflare processes that build and reduce magnetic instability prior to main-stage flares. The consistent and reliable detection and differentiation of EUV precursors could also complement and significantly improve current flare forecasting efforts.
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This content will become publicly available on February 7, 2026
The Extreme-ultraviolet Precursors and Postcursors of Solar Flares
EUV brightenings are small-scale magnetic reconnection events that consistently appear before and after solar flares. However, it is not well understood how EUV precursors might foreshadow flares and what the physical connection is between the EUV signatures and flares. We studied flare-active and inactive periods in three separate studies using the Detection and EUV Flare Tracking (DEFT) tool. In Study 1, EUV signatures were identified in 200 no-flare days, in Study 2 EUV signatures before 360 flares were analyzed, and in Study 3 close to 36,000 EUV signatures were detected, and their pre- and postflare distribution and trends were studied. Our key questions were as follows: do EUV signatures occur consistently before flares, do EUV signatures occur without flares, are there flares without EUV precursors, and is it possible to forecast different magnitude flares based on preceding EUV signature trends? Study 1 showed that in no-flare periods EUV signatures were only detected 4% of the time. Study 2 showed that EUV precursors were present 92% of the time within 6 hr before ≥C-class flares. Study 3 showed that over 90% of the signatures were associated with flares (≥B class), and over 50% of all signatures were associated with ≥M-class flares. A superposed epoch analysis showed precursor frequency peaks at ∼70 and 100 minutes before M- and X-class flares, respectively, while B- and C-class flares had no notable precursor frequency peaks. These results demonstrate the close connection between EUV signatures and flares and the significant potential EUV signatures have in improving space weather forecasting.
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- Award ID(s):
- 1931062
- PAR ID:
- 10570666
- Editor(s):
- -
- Publisher / Repository:
- IOP/AAS
- Date Published:
- Journal Name:
- The Astrophysical journal
- Edition / Version:
- -
- Volume:
- 980
- Issue:
- 1
- ISSN:
- 1538-4357
- Page Range / eLocation ID:
- 123
- Subject(s) / Keyword(s):
- -
- Format(s):
- Medium: X Size: - Other: -
- Size(s):
- -
- Sponsoring Org:
- National Science Foundation
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