Solar Photospheric Flows and the Origin of Active Regions

arXiv:2610.30333 · astro-ph.SR · Submitted 2026-10-21 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: We're looking at the paper: "Solar Photospheric Flows and the Origin of Active Regions".

Jocelyn: Here's the gist of the paper. The gist: Plasma flows appear to be determinant with respect to magnetic fields, and considered scenarios of the origin of active regions are in sharp contradiction with the rising-tube model.

Vera: The formation of active regions (ARs) and sunspot groups results from the inherently deep interaction between solar-plasma flows and magnetic fields.

Jocelyn: The basic question of heliophysical “philosophy” is whether (A) the magnetic field plays an active, primary role in the AR development or (B) this role belongs to the plasma flow.

Vera: The first view underlies the widely known rising-tube model (RTM), which assumes that an Omega-shaped loop of a flux tube of strong magnetic field emerges on the photospheric surface due to magnetic buoyancy.

Paper summary: Vera: So, we’re looking at this paper, "Solar Photospheric Flows and the Origin of Active Regions," and the whole point is trying to figure out what actually drives the making of active regions and sunspots. Is it really the magnetic field doing most of the work, or is it just how solar plasma flows around it?

Jocelyn: Right. The paper claims that we need to look at both sides—the magnetic fields and the motion of the solar plasma—to settle this big question about heliophysics. It starts by setting up a comparison between two main ideas: the rising-tube model, which says a strong magnetic loop rises, and another approach that focuses on how plasma motion itself structures those magnetic fields.

Subrahmanyan: That's the core tension, isn't it? The rising-tube model is pretty popular because it fits neatly into the overall pattern of solar activity described by things like the Hale and Sporer laws. But this paper seems to be pushing back on that idea by looking at more detailed observations.

Vera: Exactly. They use optical images from the Helioseismic and Magnetic Imager, or HMI, along with full-vector magnetic field maps to see how the actual fluid tracks look compared to where the magnetic fields are located. And what they find is pretty direct: comparing three developing active regions shows that the supergranulation pattern isn't destroyed by the emerging magnetic field.

Jocelyn: That’s a big piece of evidence against the rising-tube model because if a strong flux tube rose through those layers, you’d expect to see some kind of disruption to the surrounding cellular structure. They also noted that there are no signs of spreading flows on scales comparable to the size of these whole active regions, which is another point they bring up.

Subrahmanyan: It sounds like they're saying that whatever mechanism is happening, it doesn't seem to be a massive rising loop imposing its structure on everything around it at that early stage. This suggests that the plasma motion might be more significant in controlling the initial magnetic structure than a purely buoyancy-driven rise.

Vera: And they also looked at a well-developed sunspot group, which showed something interesting: the twist of the magnetic configuration might develop much later, even after the group has already started growing. That’s a bit counterintuitive if you think the twisting happens right when it first forms.

Jocelyn: So what this means for us observing these things is that we need to be careful about timing our expectations; we shouldn't assume the magnetic structure is fully formed right at the very beginning of an active region's life. It suggests plasma flows have a more determinant role than previously thought in how the fields evolve.

Subrahmanyan: If plasma flows are indeed determinant, then it’s not just about magnetic buoyancy pushing things up; it points toward processes like local dynamo mechanisms or hydromagnetic instabilities that are driven by convection itself, which is a much deeper way to think about structure formation.

Vera: The paper specifically highlights features in AR twelve thousand two hundred fifty-seven where the origin of the first pores seems tied to magnetic elements of mostly the same, trailing polarity. It also mentions that for AR twelve thousand four hundred new sunspots fit into the existing supergranulation pattern without disrupting it at all.

Jocelyn: That asymmetry between polarities is something they emphasize as a remarkable feature during early development, which seems to contradict a simple picture of uniform emergence. This asymmetry is key because it shows how different parts of the magnetic structure interact with the surrounding plasma flow differently.

Subrahmanyan: From a cosmological view, if convection itself can produce bipolar magnetic configurations without needing an already formed strong flux tube as a prerequisite, that opens up entirely new ways to think about how these structures get organized in the solar convection zone. It supports view B on AR formation by emphasizing the role of plasma motion.

Vera: So to wrap up what they’ve shown is that the rising-tube model isn't the only way we see ARs forming, and it seems to be in sharp contradiction with what these observations are showing us about flow dynamics versus magnetic fields.

Jocelyn: It really boils down to plasma flows appearing determinant with respect to magnetic fields in these early stages, and the paper suggests that scenarios like local dynamos or self-aggregation of magnetic elements might be more relevant than just a single rising tube.

Subrahmanyan: These findings mean that when we model structure formation on a larger scale, we can't just rely on the simple rise of a loop; we have to incorporate these complex fluid dynamics and instabilities that drive the initial organization.

Vera: So, for someone who only listens to this show, it means that when you look at an active region developing right now, don't just look for a rising tube; look closely at the flow patterns and how they interact with the existing magnetic landscape.

Jocelyn: It’s about paying attention to those subtle asymmetries and recognizing that the magnetic twist might not be built all at once, but rather developed over time through these plasma interactions.

Subrahmanyan: Ultimately, these results push us toward looking at more complex scenarios for AR origin, which means future observations need to be sensitive enough to capture these fine details of the flow dynamics.

Conclusion: Vera: So, we've seen how this paper looks at three active regions and how they compare those fluid tracks to the magnetic maps, and now we’re getting to what all this means by looking at the title and who wrote it.

Jocelyn: It's called "Solar Photospheric Flows and the Origin of Active Regions," written by Attie et al. I see a lot of talk about plasma flows being determinant with respect to magnetic fields in these early stages, right?

Subrahmanyan: Yeah, the authors are connecting this directly to the rising-tube model. They’re arguing that their scenarios are in sharp contradiction with that rising-tube model we usually think is dominant.

Vera: Exactly. The main implication here is that we might be looking at a more complex origin for active regions than just a simple loop rising on its own because the plasma motion seems to be controlling the magnetic field development from the start.

Jocelyn: So, if you only listen to this show, what does it change about how you view these sunspot groups? It suggests we need to stop thinking about the magnetic twist developing much later than when things actually start growing.

Subrahmanyan: For cosmology, this is interesting because it pushes us away from just seeing a magnetic field rising and toward looking at local dynamo mechanisms or instabilities that are driven by convection itself.

Vera: The authors flag that these results are in sharp contradiction with the rising-tube mechanism, which means we need to keep looking for alternative formation scenarios for active regions.

Jocelyn: It’s a call to action, basically—we have to study those other mechanisms like local dynamos or hydromagnetic instabilities more closely because this paper suggests they might be the real drivers.

Subrahmanyan: Right, and the next logical step is figuring out which specific observational follow-up would confirm these flow-driven scenarios instead of just confirming the simple rise of a flux tube.

Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University

astro-ph.SR

Submitted: 2026-10-21

Updated: 2026-10-21

Comments: 17 pages, 5 figures

DOI: 10.1007/s11207-026-02762-7

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 67/100

The gist: The gist: Plasma flows appear to be determinant with respect to magnetic fields, and considered scenarios of the origin of active regions are in sharp contradiction with the rising-tube model.

Key concepts

Rising-Tube Model (RTM): This popular theory suggests active regions form when a strong magnetic flux tube rises like an Omega shape due to buoyancy. The study found evidence against this, showing that the initial emergence of the field doesn't necessarily destroy the underlying supergranulation pattern.
Supergranulation Pattern: This refers to the large-scale, cellular pattern observed in the solar photosphere. The research confirmed that even as magnetic fields emerge, this regular flow pattern is not destroyed by them during early active region development.
Plasma Flows Determinism: The core conclusion is that plasma flows are more important than magnetic fields in determining AR evolution. Observations showed no evidence of spreading flows on the scale of an entire active region, suggesting material motion dictates how the magnetic field develops.
Asymmetry Between Polarities: In early active regions, the two opposite magnetic polarities often nucleate within the same supergranule and show asymmetry. This initial state is a key feature observed during the earliest stages of AR development.

Terminology

Active Regions — 1× in this paper · explained in 1 episode

Summary

The gist: Plasma flows appear to be determinant with respect to magnetic fields, and considered scenarios of the origin of active regions are in sharp contradiction with the rising-tube model.

Introduction and Core Problem

The formation of active regions (ARs) and sunspot groups results from the inherently deep interaction between solar-plasma flows and magnetic fields. The basic question of heliophysical “philosophy” is whether (A) the magnetic field plays an active, primary role in the AR development or (B) this role belongs to the plasma flow. The first view underlies the widely known rising-tube model (RTM), which assumes that an Omega-shaped loop of a flux tube of strong magnetic field emerges on the photospheric surface due to magnetic buoyancy. However, new facts contradicting the RTM have been revealed as observations became more detailed.

Evidence Against the Rising-Tube Model (RTM)

The study uses optical images and full-vector maps of the magnetic field to compare with fluid-particle tracks constructed using local correlation tracking of photospheric brightness elements. Comparisons for three developing active regions confirm that the supergranulation pattern is not destroyed by the emerging magnetic field, which would be inevitable if a loop of the strong magnetic-field flux tube rose through the subphotospheric layers. There are no signs of spreading flows on scales comparable to the size of the whole active region. Furthermore, an example of a well-developed sunspot group demonstrates that the twist of the magnetic configuration may develop much later than the group starts growing. The results show that plasma flows appear to be determinant with respect to magnetic fields.

Key Findings in Active Region Development

The analysis of specific active regions reveals several critical features regarding the interaction between material flow and magnetic field at early development stages. The essential features of AR 12257 development include:

The origin of the first pores is associated with the emergence of magnetic elements of mostly the same, trailing polarity

The development process is characterized by asymmetry between polarities, especially at its early stage. The two magnetic polarities initially nucleate within the same supergranule. Crucially, the regular supergranulation pattern is preserved for a fairly long time during this early stage. The absence of any spreading flow on the scale of the entire AR before pore formation is noted.

For AR 12400, the development pattern shows that the emergence of the sunspots does not disrupt the existing supergranulation pattern. The growth of new magnetic elements fits into the existing cellular network.

Contradictions with RTM and Alternative Mechanisms

The study highlights several features that sharply disagree with the rising-tube mechanism. Specifically:

the supergranulation pattern is not destroyed by the emerging magnetic field of the developing AR

no spreading flow is observed

The full-vector magnetic-field maps at early development stages do not exhibit signs of a helical magnetic-field structure, which would be indicative of flux-tube twisting. The twist may arise much later than the AR originates.

The paper concludes that the development of magnetic fields is controlled by plasma flows and can be attributed to class-B scenarios. Possible alternatives to the RTM include local dynamos, self-aggregation of magnetic elements into clusters, hydromagnetic instabilities causing flux concentration, and the negative effective-magnetic-pressure instability (NEMPI).

Conclusion

The results demonstrate that the RTM is neither a unique nor a dominant mechanism of AR and sunspot formation. The observed scenarios are in sharp contradiction with the rising-tube model. These findings stimulate purposeful studies of possible formation mechanisms for active regions and sunspot groups alternative to the RTM. The development of the magnetic fields of the described ARs appears to be controlled by the flows of solar plasma and can be attributed to class-B scenarios. The paper presents a brief list of some possible alternatives to the RTM.

References

Attie et al. (2018) describe, going into fine details, the moat flow around the mature sunspot in the very peculiar AR 12673 and give particular attention to the perturbations of the moat flow before strong fresh magnetic flux emerges. Birch et al. (2019) have found that their emergence is, on average, preceded by weak (20–40 m s−1) converging (rather than diverging) horizontal flows. Bobra et al. (2014) provide the data for the Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: SHARPs - Space-Weather HMI Active Region Patches. Bumba and Howard (1965) noted that in many cases, during the first days of AR development, the fluxes of the two magnetic polarities were not in balance. Cheung et al. (2007) discuss magnetic flux emergence in granular convection. Chumak (2013) suggests that the self-organization of local magnetoplasma structures in the upper layers of the solar convection zone seems quite plausible. Getling and Buchnev (2019) discuss the origin and early evolution of a bipolar magnetic region in the solar photosphere. Grigoryev et al. (2025) examine the effects of a twisted magnetic rope at the stage of the appearance of a new active region in the photosphere. Stein and Nordlund (2012) demonstrate that convection itself can produce bipolar magnetic configurations without an initially present coherent strong-magnetic-flux tube. Warnecke et al. (2016) report bipolar region formation in stratified two-layer turbulence. Weber et al. (2023) suggest that flux emergence may be a more passive process dominated to a greater extent by the influence of convection and to a lesser extent by buoyancy and the Coriolis force acting on rising magnetic flux tubes than previously thought. Zagainova et al. (2022) study the magnetic properties of sunspot umbrae. Zhao et al. (2013) report detection of equatorward meridional flow and evidence of double-cell meridional circulation inside the Sun. Tverskoi (1966) contributed to the theory of hydrodynamic self-excitation of regular magnetic fields. Leka et al.

Improvements for AI systems

Improved AR formation prediction by distinguishing between magnetic field dominance and plasma flow dominance. The system can now predict whether an active region's evolution is better described by a rising-tube model or mechanisms dominated by in situ magnetic-field amplification and structuring by plasma motion, based on observational comparisons of optical and magnetic maps.
Enhanced supergranulation pattern tracking for AR development. The system can now track the supergranulation pattern as it evolves during active region formation, confirming whether it is not destroyed by the emerging magnetic field of the developing AR, providing a more detailed understanding of photospheric structure changes.
Asymmetric polarity prediction in sunspot group evolution. The AI can predict and characterize the asymmetry between leading and trailing magnetic polarities in developing active regions, as demonstrated by observing that the development pattern of the two magnetic polarities is enormously asymmetric.
Verification of the absence of large-scale spreading flows. The system can identify and confirm that no signs of solar-plasma spreading on scales no less than the size of the whole AR are observed during early development, directly contradicting predictions from models involving flux tube rise.
Helical structure detection in magnetic fields. The AI can detect whether a pronounced helical structure of the leading sunspot magnetic field is present during late development stages, allowing it to differentiate between AR formation associated with a rising twisted flux tube and later twisting processes.

Abstract

The early evolutionary stages of some active regions (ARs) are analysed with the aim of resolving one of the paramount-importance problems of heliophysics: what plays a primary, active role in the formation of active regions and sunspots---magnetic fields or motion of solar plasma? In particular, the first view underlies the popular model of rising Ω-shaped, twisted flux-tube loop of strong magnetic field. In this study, optical images obtained by the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory are used along with full-vector maps of magnetic field based on HMI data. Maps of fluid-particle tracks are constructed using local correlation tracking of photospheric brightness elements. Comparisons of optical and magnetic maps for three developing active regions confirm the conclusion made by Bumba and Howard in the mid-1960s that the supergranulation pattern is not destroyed by the emerging magnetic field of the developing AR, which would be inevitable if a loop of the strong-magnetic-field flux tube rose through the subphotospheric layers. There are no signs of spreading flows on scales comparable to the size of the whole active region. Various forms of dissymmetry between the leading and trailing parts of ARs are revealed. Next, an example of a well-developed sunspot group is considered, which demonstrates that the twist of the magnetic configuration may develop much later than the group starts growing. It is concluded that plasma flows appear to be determinant with respect to magnetic fields. The considered scenarios of the origin of ARs are in sharp contradiction with the rising-tube model.