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arxiv: 2606.09562 · v1 · pith:2DPNTENDnew · submitted 2026-06-08 · 🌌 astro-ph.SR

Apparent Transverse Motion of Light Bridges Coupled to Coronal Loop Dynamics

Atul Bhat , Sreejith Padinhatteeri , J.M. Borrero , Jayant Joshi This is my paper

Pith reviewed 2026-06-27 15:01 UTC · model grok-4.3

classification 🌌 astro-ph.SR
keywords light bridgessunspotscoronal loopsumbral dynamicsapparent motiontransverse motionsolar atmosphere coupling
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The pith

Light bridge transverse motions in sunspots are apparent projections of umbral core dynamics coupled to coronal loops.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper analyzes two instances of unusual light bridge evolution inside a sunspot using Solar Dynamics Observatory data. It reports that the sideways motions seen in the light bridges match the timing and direction of changes in the surrounding umbral core. The authors interpret these motions as projections rather than real sideways shifts of the bridges themselves. They further trace the same dynamical signatures upward and find they align with the evolution of overlying coronal loops. This establishes a proposed connection between photospheric umbral activity and coronal structures.

Core claim

The unique movements of the light bridges in the observed sunspot and earlier studies could be an apparent view of the umbral core dynamics. Investigation into these dynamics through signatures in the higher atmosphere reveals a clear coupling to coronal loops and their dynamics.

What carries the argument

Apparent transverse motion of light bridges, treated as a line-of-sight projection of umbral core evolution whose signatures propagate upward to drive or follow coronal loop changes.

If this is right

  • Light bridge observations can serve as indirect indicators of umbral core evolution.
  • Coronal loop dynamics are dynamically linked to photospheric umbral processes through the light bridge region.
  • Earlier reports of light bridge motion in other sunspots may also reflect apparent rather than intrinsic bridge displacement.
  • Signatures in the chromosphere and corona can be used to monitor umbral core changes when photospheric resolution is limited.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same projection effect may explain light bridge behavior across multiple active regions, allowing a single mechanism to account for diverse reported motions.
  • Routine coronal imaging could become a practical tool for tracking internal sunspot restructuring on timescales shorter than those accessible from the photosphere alone.
  • Magnetoconvective models of sunspots would need to include upward coupling channels from the umbra through light bridges to the corona.

Load-bearing premise

The observed sideways shifts of light bridges are projections caused by deeper umbral core motion rather than actual physical displacement of the light bridge material.

What would settle it

High-resolution vector magnetograms or Doppler maps showing light bridge material undergoing genuine lateral displacement with no corresponding change in the umbral core or in the connected coronal loops.

Figures

Figures reproduced from arXiv: 2606.09562 by Atul Bhat, Jayant Joshi, J.M. Borrero, Sreejith Padinhatteeri.

Figure 1
Figure 1. Figure 1: Normal contrast (a frames) and the corresponding enhanced contrast (b frames) images of the sunspot in AR 13590. Each tick on the x and y axes represents latitude and longitude in Stonyhurst coordinates, respectively. The coordinates of a frames are the same as the corresponding b frames. The timestamps apply to each frame-pair. These panels show the S-light bridge visibly appearing and evolving, before di… view at source ↗
Figure 2
Figure 2. Figure 2: The Ω-light bridge observed on 22 Feb 2024. The top row shows the normal contrast images from HMI and the bottom row shows the same images with enhanced contrast. The light bridge forming the Ω shape shape is visible in frame i.The Animation shows normal contrast and enhance contrast frames, side-by-side, of time-evolution of the light bridges for the duration of 24 hours on 22 Feb 2024. row in [PITH_FULL… view at source ↗
Figure 3
Figure 3. Figure 3: Continuum intensity AR 13590 (top row) showing a cut across the light bridge (cyan line); the magnetic field intensity, vertical component of the magnetic field, horizontal component of the magnetic field and inclination with respect to LOS (subsequent rows; blue) plotted along line across the light bridge at various timestamps. The ticks in the top row are latitude and longitude in Stonyhurst coordinates.… view at source ↗
Figure 5
Figure 5. Figure 5: VLOS for the sunspot with Ω-light bridge. Con￾tours same as [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 4
Figure 4. Figure 4: VLOS for the sunspot with the S-light bridge. Contours are plotted for intensity at 0.4IQS (outer) and 0.09IQS (inner) plotted over it. CEFs are observed along the arm of the S-light bridge as it initially extends and when it recedes back. No CEFs are observed along the tail of the light bridge. The large values in the core-umbra (marked by the gray contour) may be due to saturation effects and other facto… view at source ↗
Figure 6
Figure 6. Figure 6: The S-light bridge of AR 13590 in photosphere (HMI enhanced contrast - First row) and the chromosphere (AIA 1700˚A - middle row and AIA 1600˚A - bottom row). Left columns (4:36 UT) show brightening in the AIA frames along the arm of the LB. The right frames (16:48 UT) show both the arm and the tail of the LB, through contours marked for 0.09IQS in the AIA frames The red contour in the HMI frames mark the u… view at source ↗
Figure 7
Figure 7. Figure 7: The Ω-light bridge of AR 13590 in photosphere (HMI enhanced contrast - left) and the chromosphere (AIA 1600˚A - middle and AIA 1700˚A - right). The contours are marked for 0.09IQS in the AIA frames and the red contour in the HMI frames mark the umbral boundary. The light bridge is not visible in the AIA frames. Each tick marks 25 pixels. brightening, the tail shows no signatures in the AIA frames. Since on… view at source ↗
Figure 8
Figure 8. Figure 8: A 420”×420” FOV of the AR 13590 in AIA 171˚A at various timestamps on 23 Feb 2024. The umbra with the S-light bridge is marked with cyan contour (marked by white arrow in frame ’a’). The white lines with central gaps indicate the coronal loops (visible between the gaps). A faint coronal loop forms (frame ’b’ & ’c’) with its footpoints (marked by arrow in frame ’c’) in the sunspot. Another loop (frame ’e’ t… view at source ↗
Figure 9
Figure 9. Figure 9: The sunspot from [PITH_FULL_IMAGE:figures/full_fig_p009_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: SpaceTime (st) plots of artificial slits on coronal loops (top) and the light bridge (bottom) in AR 13590 on 23 Feb 2024. The left square plots show the position of the slit on the features and the plots on the right are the slits over time. The occurrence of loop shown in [PITH_FULL_IMAGE:figures/full_fig_p010_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: 135”×100” frames from AIA 171˚A centered at the umbra (cyan contour for 0.09IQS) for S-light bridge. The small loops correspond to LB events discussed in last subsec￾tion in § 4. Frames a and c show the pre-loop stages, while frame b shows the small coronal loop (pointed by the arrow), which occurs as the LB arm and tail break and c frame d shows another such loop when the tail disappears. loops (M. J. As… view at source ↗
Figure 12
Figure 12. Figure 12: SpaceTime (st) plots of artificial slits across coronal loops (middle) and the Ω light bridge (bottom) in AR 13590 on 22 Feb 2024. The square plots on the top show the position of the slit (slit from left to right) on the features and the plots on the right are the slits over time. The expansion of the loop shown in [PITH_FULL_IMAGE:figures/full_fig_p011_12.png] view at source ↗
Figure 13
Figure 13. Figure 13: Frames from AIA 171˚A at during the Ω-light bridge evolution on 22 Feb 2024. The umbral core regions are contoured in white. The coronal loop is marked with the white arrow in first and last frames. The coronal loop footpoint show lateral expansion in each frame [PITH_FULL_IMAGE:figures/full_fig_p012_13.png] view at source ↗
Figure 14
Figure 14. Figure 14: Bitmap images of the umbral core regions around the S-light bridge (Identified with I ≤ 0.075IQS and |B| > 2kG ), marked 1, 2 and 3. The umbral contour (I < 0.09IQS) is marked in red. The footpoints (2 & 3) move in the anti-clockwise direction [PITH_FULL_IMAGE:figures/full_fig_p012_14.png] view at source ↗
Figure 16
Figure 16. Figure 16: The umbral core regions of AR 13590 on 22 Feb, around the Ω-light bridge at 17:36 and 22:00. A line is drawn along extended length of the umbral core region to measure the change in width (red line). The extension is shown in cyan. Each tick marks 10 pix. which are the footpoints of the coronal loop, causes the transverse motion of the coronal loop. This effect is illustrated in the cartoon depicted in [… view at source ↗
Figure 17
Figure 17. Figure 17: A cartoon of the coronal loop footpoints (yel￾low) within AR 13590; top: around the S-light bridge, the umbral cracks (marked by ’gray’ line within ’black’ umbra) forms around the two footpoints, passing in between them; bottom: around the Ω-light bridge, the coronal loop foot￾point expands laterally pushing the umbral cracks. correlation between their evolution and the motion of the coronal loop footpoin… view at source ↗
read the original abstract

Light bridges are commonly observed in active regions and are interpreted as signatures of magnetoconvective processes in sunspots. Several studies have attempted to classify them in the past based on their morphological characteristics. Recent observations have revealed new dynamical properties of light bridges, including their signatures in the upper solar atmosphere, particularly in the chromosphere, and their coupling with coronal features. In this study, we observed two cases of rare and unusual dynamics as light bridges evolve. Using data from the Solar Dynamics Observatory, the evolution of the light bridges is analysed, and the results are reported here. Based on our findings, we propose that the unique movements of the light bridges in the observed sunspot and earlier studies could be an apparent view of the umbral core dynamics. Investigation into these dynamics through signatures in the higher atmosphere reveals a clear coupling to coronal loops and their dynamics.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The manuscript reports observations of two cases of unusual transverse motions in light bridges within sunspots, analyzed using Solar Dynamics Observatory (SDO) data. The authors propose that these movements represent an apparent projection of umbral core dynamics coupled to coronal loop dynamics, as revealed through signatures in the higher atmosphere.

Significance. If the interpretation holds and is supported by the underlying data, the work could provide a new perspective on the coupling between photospheric magnetoconvective features and coronal structures. The paper is purely observational with no equations, derivations, fitted parameters, or machine-checked elements; its value rests entirely on the quality and presentation of the two cases.

major comments (1)
  1. [Abstract] Abstract: the central interpretive proposal (that light-bridge motions are apparent projections of umbral-core dynamics) rests on unspecified analysis of two cases, yet the abstract provides no data, figures, error analysis, or methods. This prevents evaluation of whether the claim is supported by evidence and is load-bearing for the manuscript's main conclusion.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their review and constructive comment. We address the point below and will revise the manuscript accordingly.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the central interpretive proposal (that light-bridge motions are apparent projections of umbral-core dynamics) rests on unspecified analysis of two cases, yet the abstract provides no data, figures, error analysis, or methods. This prevents evaluation of whether the claim is supported by evidence and is load-bearing for the manuscript's main conclusion.

    Authors: We agree that the abstract as written is too terse and does not sufficiently indicate the observational basis for the central claim. The manuscript presents two specific cases drawn from SDO/AIA and HMI data, with the interpretation arising from the apparent transverse motions in the light bridges being consistent with projected umbral-core dynamics and their coupling to overlying coronal loops. In revision we will expand the abstract to state the data sources, note the two observed cases, and briefly characterize the key signatures (transverse motions aligned with coronal-loop evolution) that support the projection interpretation, while keeping the abstract concise. Detailed measurements, time series, and comparison with earlier studies remain in the body of the paper. revision: yes

Circularity Check

0 steps flagged

No significant circularity

full rationale

The paper is a purely observational report analyzing SDO data on light-bridge evolution in sunspots. It presents no equations, derivations, fitted parameters, or mathematical predictions. The central claim is an interpretive proposal linking observed motions to umbral-core dynamics and coronal loops, explicitly flagged as 'apparent' in the title and abstract. No self-citation chains, ansatzes, or reductions of outputs to inputs by construction are present. The derivation chain is absent, so no circularity can be exhibited.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The paper is an observational report with no mathematical derivations, free parameters, or new physical entities postulated; the central claim rests on data interpretation rather than axioms or models.

pith-pipeline@v0.9.1-grok · 5689 in / 1015 out tokens · 29275 ms · 2026-06-27T15:01:44.246185+00:00 · methodology

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