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SADCat: A Catalog of Supra-Arcade Downflow Events in Solar Flares

This paper introduces SADCat, a manually compiled catalog of 178 supra-arcade downflow-producing solar flares from solar cycle 24, and presents a preliminary analysis revealing that peak X-ray flux, flare duration, CME speed, and CME mass significantly influence the visibility of SADs, while impulsivity and acceleration do not.

Original authors: Trestan F. Simon, Ryan J. French

Published 2026-07-07

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CC BY 4.0

Original authors: Trestan F. Simon, Ryan J. French

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the Sun as a giant, chaotic kitchen where magnetic "rubber bands" are constantly snapping, twisting, and re-tying themselves. When these bands snap too hard, they create a massive explosion called a solar flare. Often, this explosion kicks up a huge cloud of solar material called a Coronal Mass Ejection (CME), which is like a tidal wave of plasma shooting out into space.

In the aftermath of these explosions, right above the "arcade" of magnetic loops (think of them as the arches of a bridge), scientists have noticed something strange: dark, tadpole-shaped voids that swim downward toward the Sun. These are called Supra-Arcade Downflows (SADs).

For a long time, these SADs were like ghosts in the machine—seen occasionally, but not well understood. This paper, titled SADCat, is essentially the first comprehensive "phone book" or catalog of these ghostly events.

Here is a simple breakdown of what the authors did and what they found:

1. The Great Hunt (The Catalog)

The authors, Trestan Simon and Ryan French, decided to create a master list of every time these SADs appeared. They looked at data from the Solar Dynamics Observatory (SDO), a satellite that takes high-definition movies of the Sun, covering a period of about nine years (Solar Cycle 24).

The Process: They started with over 14,000 solar flares. They filtered out the ones that were too small, the ones happening on the far side of the Sun (where we couldn't see them clearly), and the ones that didn't have a matching CME (since SADs only happen with big eruptions).
The Result: After manually watching movies of the remaining candidates, they found 178 specific flares where SADs were clearly visible. They compiled all the details (time, size, speed, location) into a database they call SADCat. Think of this as a "Hall of Fame" for solar explosions that produced these specific downward-swimming voids.

2. The Detective Work (What Makes a SAD?)

Once they had their list of 178 "SAD flares," they compared them to a list of 834 "non-SAD flares" (explosions that happened but didn't show the tadpole voids). They wanted to see if there was a pattern: What makes a flare produce a SAD?

They compared the "personality" of the flares and the CMEs:

The Size of the Party (Flare Strength): They found that bigger, stronger flares are much more likely to produce SADs. It's like a loud, energetic party is more likely to have a specific type of dance move than a quiet gathering.
The Duration (How Long it Lasts): SADs are more common in long-lasting flares. If a flare burns for a long time (over 30 minutes), it's a good bet that SADs will show up.
The Speed of the Wave (CME Speed): This was a big surprise. SADs are strongly linked to fast-moving CMEs. If the solar tidal wave is shooting out at high speeds, SADs are likely to appear.
The Weight of the Wave (CME Mass): Similarly, SADs are more common when the CME is massive (heavy with solar material).
The "Surprise" Factors: Interestingly, they found that how fast the flare started (impulsivity) and how fast the CME accelerated didn't really matter. A slow-starting, steady explosion can still produce SADs, just as a fast-starting one can.

3. The Big Picture

The authors aren't claiming to have solved the mystery of exactly what SADs are made of or why they form. Instead, they are providing the ingredients list for future scientists.

They are saying: "If you are building a computer model or a theory to explain SADs, your model must be able to explain why SADs show up in big, long, heavy, and fast events, but not necessarily in fast-starting or short ones."

Summary Analogy

Imagine you are trying to figure out why some people in a crowd start doing a specific wave (the SAD).

You look at 14,000 different crowds (flares).
You realize the wave only happens in the big, loud, long-lasting concerts (strong, long-duration flares) where the mosh pit is moving very fast and is very heavy (fast, massive CMEs).
You don't care if the music started suddenly or slowly (impulsivity/acceleration).
You write down a list of the 178 concerts where the wave happened so other researchers can study the crowd dynamics.

That is what SADCat is: a curated list of the "concerts" where the solar wave happened, helping scientists understand the rules of the solar dance floor.

Technical Summary: SADCat: A Catalog of Supra-Arcade Downflow Events in Solar Flares

Problem and Motivation
Supra-arcade downflows (SADs) are sunward-traveling, low-density features routinely observed in hot fan structures above magnetic loop arcades during eruptive solar flares. While SADs have been identified in imagery from various instruments (including Yohkoh, Hinode, SOHO, and SDO/AIA) since their discovery, previous studies have largely focused on small samples (typically $\lesssim 10$ flares) or individual SAD structures within single events. Prior to this work, no comprehensive catalog of SAD-productive flares derived from the high-cadence, full-disk EUV imagery of the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) existed. The authors identify a need for a standardized resource to facilitate statistical analysis of SAD formation mechanisms and their relationship to global flare and Coronal Mass Ejection (CME) properties.

Methodology
The authors constructed "SADCat," a catalog of 178 SAD-associated eruptive flares observed during solar cycle 24 (May 13, 2010 – December 31, 2019). The methodology involved a multi-stage filtering and manual verification process:

Candidate Selection: Starting from the Hinode Flare Catalog (14,781 events), the authors filtered for flares with a peak GOES 1–8 Å flux $\geq 10^{-6}$ W m $^{-2}$ (C1.0 class) and originating from source regions with unsigned heliographic Stonyhurst (HS) longitude $\geq 65^\circ$ . This yielded 3,552 candidate flares, a constraint chosen to prioritize limb events where SADs are most visible and to ensure sufficient SXR emission.
Eruptive Correlation: Candidates were cross-referenced with the SOHO/LASCO CME Catalog (CDAW). A flare was deemed "eruptive" if a CME was detected between the flare's start time and 80 minutes post-peak, with an angular separation between the flare source and CME central position angle $\leq$ half the CME width or $45^\circ$ . This reduced the list to 1,015 flares associated with 921 unique CMEs.
Manual Identification: SDO/AIA 131 Å cutouts (400" $\times$ 400") were generated for each candidate, spanning from flare start to 120 minutes post-end. Images were processed using square-root transformation, multi-scale Gaussian normalization (MGN), and time-difference techniques to enhance contrast. A single author manually inspected the resulting movies to identify SADs (defined as tadpole- or teardrop-like voids traveling toward arcade looptops).
Final Catalog: This process resulted in 178 confirmed SAD events (18% of candidates) and 834 non-SAD events. The catalog includes peak time, duration, impulsivity, GOES class, source region coordinates, and CME speed and mass.

Key Contributions

SADCat: The primary contribution is the release of a comprehensive catalog of 178 SAD-productive flares, available both in tabular format and online. This is the first such catalog based on AIA data covering the entirety of solar cycle 24.
Standardized Dataset: The catalog provides a consistent set of flare and CME parameters (derived from GOES, Hinode, and CDAW) specifically for events where SADs were visually confirmed, enabling comparative studies between SAD and non-SAD events.

Results and Preliminary Analysis
The authors conducted a statistical comparison between the 178 SAD events and the 834 candidate flares without visible SADs. Key findings include:

Flare Properties: SADs are significantly more likely to occur in flares with higher peak GOES flux and longer durations.
- 44% of SAD flares were M-class or higher, compared to only 15% of non-SAD flares.
- The average duration for SAD flares was $62 \pm 4$ minutes, compared to $27 \pm 1$ minutes for non-SAD flares. 65% of SAD flares were "long-duration events" (>30 min), versus 25% of non-SAD flares.
- Flare impulsivity showed no significant difference between the two groups (averages of 0.526 vs. 0.523).
CME Properties: SADs are strongly correlated with faster and more massive CMEs, but not with CME acceleration.
- Average CME speed for SAD events: $745 \pm 37$ km s $^{-1}$ ; for non-SAD events: $396 \pm 9$ km s $^{-1}$ .
- 63% of SAD-associated CMEs exceeded 500 km s $^{-1}$ , compared to 25% of non-SAD CMEs.
- 76% of SAD-associated CMEs had masses $> 10^{15}$ g, compared to 28% of non-SAD CMEs.
- CME acceleration distributions were similar for both groups (averages of $-5.1 \pm 2.6$ m s $^{-2}$ vs. $-1.1 \pm 1.1$ m s $^{-2}$ ).

Significance and Claims
The authors claim that this work provides the first quantitative demonstration of the relationship between SAD occurrence and flare/CME magnitude. They posit that the correlation with flare duration and peak flux is likely due to the production of brighter, more extensive supra-arcade fans in larger events, which facilitates the detection of SADs.

Regarding CMEs, the authors note that the association with faster and more massive CMEs is a novel finding not previously reported quantitatively. They offer a tentative theoretical interpretation: faster CMEs may evacuate the corona more rapidly, leaving a weaker magnetic field in the wake of the flare current sheet, potentially creating an environment where SADs grow large enough to be detectable. However, the authors explicitly state that providing a robust physical interpretation is beyond the scope of this paper and likely requires Magnetohydrodynamic (MHD) modeling.

The paper concludes by emphasizing that SADCat serves as a foundational resource for the solar flare community. Future theoretical and computational models of SAD formation must be compatible with these statistical relationships. The authors also note plans to extend the catalog beyond solar cycle 24 and explore machine-learning techniques for event identification in the future.

1. The Great Hunt (The Catalog)

2. The Detective Work (What Makes a SAD?)

3. The Big Picture

Summary Analogy

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