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Application of the coherent structure tracking to solar Doppler maps to determine horizontal velocity fields at the Sun's surface

T0 review · 2 major / 2 minor · reviewed 2026-06-26 · grok-4.3

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Pith's one-line read Coherent structure tracking applied to solar Dopplergrams yields horizontal velocity fields matching those from intensity images.

desk verdict CST on Dopplergrams correlates at 73% globally with intensity-based flows, a useful check but not evidence they deliver the same reliability. read the letter →

arxiv 2606.17544 v1 pith:ME5CV45E submitted 2026-06-16 astro-ph.SR

M. Sampoorna , T. Roudier , F. Paletou This is my paper · ORCID
classification astro-ph.SR
keywords coherentstructuretrackingsolargranulationDopplergramshorizontalvelocityfieldsSDO/HMIsurfaceflowsgranularpropermotion
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper tests whether Coherent Structure Tracking, which follows the motion of granules to map flows across the Sun's surface, works as reliably on Doppler velocity maps as on the usual continuum intensity images. By running CST on both types of data from SDO/HMI observations and from a numerical simulation of granulation, the authors measure global and local correlations between the resulting velocity fields, their divergence, and their curl. Correlations reach 73 percent globally and 80 percent locally near disk center for 30-minute averages on a quiet Sun, rising with longer averaging times and falling only modestly in more active regions. This opens an alternative data source for surface flow measurements since Dopplergrams are already collected routinely.

What carries the argument

Coherent Structure Tracking (CST), the method that follows proper motions of granular structures visible in images or maps to recover horizontal flow vectors.

What would settle it

Finding global correlation coefficients below 50 percent between CST velocity fields from Dopplergrams and from intensity images on a new independent dataset or during a strongly magnetic period would falsify the claim of equivalent reliability.

Watch

Extended reading notes

Core claim

CST applied to Dopplergrams produces horizontal velocity fields whose Pearson global correlation coefficient with intensity-derived fields is about 73 percent for 30-minute averages, with local correlation near disk center at 80 percent for velocity and 84 percent for divergence. The same comparison on a numerical simulation of granulation shows high agreement, and the correlation coefficients improve steadily as the time window increases while decreasing slightly in regions containing sunspots or emerging pores.

Load-bearing premise

Granulation patterns in Dopplergrams move in ways that directly reflect horizontal flows without large contamination from vertical velocities or magnetic effects.

Editorial extensions

If this is right

  • Horizontal velocity fields from Doppler CST agree with intensity CST at 73 percent global correlation for 30-minute averages.
  • Divergence fields reach 72 percent global and 84 percent local correlation near disk center.
  • Correlation values rise as the averaging time window lengthens.
  • Agreement remains high but decreases modestly in the presence of sunspots or emerging pores.
  • CST on simulated intensity and vertical-velocity maps also produces closely matching horizontal flows.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • Doppler-based CST could supply flow maps in spectral lines or instruments where continuum intensity granulation is weak or unavailable.
  • Combined Doppler and intensity CST might help isolate true horizontal motions from projection or vertical-velocity artifacts.
  • Routine use on Doppler data could support continuous surface-flow monitoring for studies of solar convection and magnetic flux transport.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 2 minor

Summary. The manuscript applies the Coherent Structure Tracking (CST) technique to solar Dopplergrams from SDO/HMI and a numerical simulation of granulation, comparing the derived horizontal velocity fields and their derivatives (divergence and curl) to those obtained from continuum intensity images. It reports Pearson global correlation coefficients (GCC) of ~73% for velocity fields and ~72% for divergence over 30-minute averages (higher locally near disk center), with values increasing for longer averaging windows and slightly decreasing in more active regions, concluding that CST on Dopplergrams achieves comparable reliability.

Significance. If the moderate correlations can be shown to arise from understood and correctable effects rather than fundamental limitations, the work would enable the use of Doppler data for high-resolution flow tracking, complementing intensity-based methods and potentially improving measurements in varied solar conditions. The inclusion of a numerical simulation validation, where high correlation is reported between intensity and vertical velocity maps, is a positive aspect demonstrating internal consistency in controlled conditions.

major comments (2)
  1. [Abstract] Abstract: The central claim that CST applied to Dopplergrams yields horizontal velocity fields 'with the same level of confidence' as intensity-based CST is not borne out by the reported GCC of 73% (30 min average) and 72% for divergence; these values imply ~27-28% unexplained variance, and the manuscript does not isolate or quantify contributions from vertical velocities contaminating the Doppler granulation pattern or from differing noise properties.
  2. [Abstract] Abstract: No error bars, uncertainty estimates, or details on data exclusion criteria (e.g., for magnetic regions or limb effects) are provided for the correlation coefficients, making it difficult to assess the statistical significance of the reported differences between active and quiet Sun or between components (velocity, divergence, curl).
minor comments (2)
  1. The abstract refers to 'a relatively less active Sun' and 'magnetically more active Sun' without quantitative metrics such as average magnetic field strength or sunspot number for the selected periods.
  2. Spearman's and Kendall's coefficients are mentioned as following a similar trend but no specific values are given, which would aid comparison to the Pearson results.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for their thoughtful comments on our manuscript. We address each major comment below and indicate where revisions will be made to improve clarity and provide additional statistical information.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The central claim that CST applied to Dopplergrams yields horizontal velocity fields 'with the same level of confidence' as intensity-based CST is not borne out by the reported GCC of 73% (30 min average) and 72% for divergence; these values imply ~27-28% unexplained variance, and the manuscript does not isolate or quantify contributions from vertical velocities contaminating the Doppler granulation pattern or from differing noise properties.

    Authors: We acknowledge that the phrase 'same level of confidence' may overstate the case given the reported correlations of approximately 73%. We will revise the abstract to describe the results as achieving 'comparable reliability', aligning with the manuscript's conclusion section. The numerical simulation shows high correlation between CST on intensity and vertical velocity maps, supporting that the Doppler granulation pattern enables reliable horizontal flow tracking. While we do not provide a detailed decomposition of the unexplained variance into vertical velocity effects and noise, the overall correlations and the simulation validation indicate the method's viability. We will add a brief discussion of these potential sources in the revised text. revision: partial

  2. Referee: [Abstract] Abstract: No error bars, uncertainty estimates, or details on data exclusion criteria (e.g., for magnetic regions or limb effects) are provided for the correlation coefficients, making it difficult to assess the statistical significance of the reported differences between active and quiet Sun or between components (velocity, divergence, curl).

    Authors: We agree that including uncertainty estimates and details on data selection would strengthen the manuscript. In the revision, we will provide error bars on the correlation coefficients (e.g., using bootstrap methods or standard errors), specify the criteria used for excluding or masking magnetic regions, and discuss any considerations for limb effects in the data analysis. revision: yes

standing simulated objections not resolved
  • Complete isolation and quantitative decomposition of the contributions from vertical velocity contamination and noise properties to the ~27% unexplained variance in the correlations.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity; empirical comparison of independent CST applications

full rationale

The paper's central claim rests on applying the CST algorithm independently to two distinct observables (continuum intensity images and Dopplergrams) from SDO/HMI and a numerical simulation, then reporting empirical Pearson, Spearman, and Kendall correlations between the resulting horizontal velocity fields and their derivatives. No parameters are fitted to the target correlations, no velocity field is defined in terms of itself, and no load-bearing step reduces to a self-citation or ansatz. The derivation chain consists of straightforward observational validation and is therefore self-contained.

Assumptions & free parameters 0 free parameters · 1 assumptions · 0 invented entities

Abstract-only review; no explicit free parameters, invented entities, or additional axioms beyond the core domain assumption that granules are trackable in Doppler data.

assumptions (1)
  • domain assumption Granulation patterns are visible and trackable in Dopplergrams similarly to intensity images.
    Explicit premise stated in the abstract for applying CST to Doppler data.

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Cite this review

Pith. "Pith review of Application of the coherent structure tracking to solar Doppler maps to determine horizontal velocity fields at the Sun's surface." pith.science (2026). https://pith.science/paper/ME5CV45E

@misc{pith2026260617544,
  author       = {Pith},
  title        = {Pith review of: Application of the coherent structure tracking to solar Doppler maps to determine horizontal velocity fields at the Sun's surface},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/ME5CV45E}},
  note         = {Machine review of arXiv:2606.17544}
}
read the original abstract

Coherent Structure Tracking (CST) is a technique for determining the solar surface horizontal flows at high spatial and temporal resolution by tracking the proper motion of granules. CST has been traditionally applied to solar intensity images in the continuum, which clearly depict the granular patterns. However, solar granulation is also visible in the Dopplergrams. We aim to show that CST can be applied to solar Dopplergrams to derive the solar surface horizontal velocity fields with the same level of confidence as those determined by CST on intensity images. For this purpose, we apply the CST to continuum intensity images and Dopplergrams obtained from SDO/HMI and also from a numerical simulation of granulation. We then compare the resulting solar surface horizontal velocity fields and their derivatives for different time windows. Pearson's linear global correlation coefficient (GCC) between the horizontal velocity fields determined from CST on Doppler and on intensity images of a relatively less active Sun is about 73% for a 30 min time average, while the corresponding local correlation coefficient (LCC) near the disk center is about 80%. For the divergence of the horizontal velocity field, we obtain a GCC of 72% and a near disk center LCC of 84%. The curl of the horizontal velocity field being more noisy exhibits somewhat reduced GCC and LCC. These coefficients increase with increasing time window. A similar trend is exhibited by Spearman's and Kendall's rank-order correlation coefficients, although they are somewhat smaller in value. The different correlation coefficients slightly decrease for magnetically more active Sun with sunspots or emerging pores in a plage region. A high correlation is obtained between the horizontal flows derived by applying CST to intensity and vertical velocity maps from a numerical simulation.

Figures

Figures reproduced from arXiv: 2606.17544 by the authors.

Figure 1
Figure 1. Left : Horizontal velocity vector (Vx , Vy) determined by applying the CST to vertical ve￾locity (Vz) map obtained from a numerical sim￾ulation of granulation. Right : The residual vec￾tor between the horizontal velocities obtained by applying the CST to intensity and vertical velocity map from simulation. A temporal win￾dow of 30 min is used. The arrow to the bot￾tom right corner of each panel shows the length of t… view at source ↗
Figure 2
Figure 2. Left : Horizontal velocity vector (Vx , Vy) determined by applying the CST to Dopp￾lergrams from 29th of December 2022 observa￾tions of SDO/HMI is shown for a region near the disk center and for a temporal window of 30 min. Right : The residual vector between the horizontal velocities obtained by applying the CST to intensity and Doppler maps from the above-said observations is shown for the same region and time win… view at source ↗
Figure 3
Figure 3. Histogram of the amplitude of the hori￾zontal velocity field (panels (a), (c), (e)) and the difference in velocity amplitude obtained from CST on intensity and Dopplergrams (panels (b), (d), (f)) for 30 (panels (a) and (b)), 60 (panels (c) and (d)), and 120 (panels (e) and (f)) minutes time window. In the left panels, we also shown the histogram of the scalar product (see Eq. (3)) between the horizontal velocities o… view at source ↗
Figures from the paper (2 more)
Figure 4
Figure 4. Figure 4: Horizontal velocity vector (Vϕ, Vθ) derived by applying CST to intensity (left column) and Doppler (right column) maps observed by SDO/HMI on 28th of May 2023. Field of view covers the region around the sunspots near to the equator. The top, middle, and bottom rows cor…
Figure 5
Figure 5. Figure 5: Horizontal velocity vector (Vϕ, Vθ) de￾rived by applying CST to intensity (left col￾umn) and Doppler (right column) maps ob￾served by SDO/HMI on 29th of May 2023. Field of view covers the plage region with emerging pores near to the equator. The top to bottom rows corr…

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Works this paper leans on

30 extracted references

  1. [1]

    S., & Vitas, N

    Asensio Ramos, A., Requerey, I. S., & Vitas, N. 2017, A&A, 604, A11

    2017

  2. [2]

    2014, ApJ, 788, 127

    DeGrave, K., Jackiewicz, J., & Rempel, M. 2014, ApJ, 788, 127

    2014

  3. [3]

    L., Jefferies, S

    Duvall, Jr., T. L., Jefferies, S. M., Harvey, J. W., & Pomerantz, M. A. 1993, Nature, 362, 430

    1993

  4. [4]

    Fisher, G. H. & Welsch, B. T. 2008, in Astronomical Society of the Pacific Con- ference Series, V ol. 383, Subsurface and Atmospheric Influences on Solar Activity, ed. R. Howe, R. W. Komm, K. S. Balasubramaniam, & G. J. D. Petrie, 373

    2008

  5. [5]

    2023, A&A, 675, A182

    Kamlah, R., Verma, M., Denker, C., & Wang, H. 2023, A&A, 675, A182

    2023

  6. [6]

    2023, Sol

    Li, Q., Xu, Y ., Verma, M., et al. 2023, Sol. Phys., 298, 62 Löhner-Böttcher, J. & Schlichenmaier, R. 2013, A&A, 551, A105 Löptien, B., Birch, A. C., Duvall, T. L., et al. 2017, A&A, 606, A28

    2023

  7. [7]

    E., Ravindra, B., Georgoulis, M

    Louis, R. E., Ravindra, B., Georgoulis, M. K., & Küker, M. 2015, Sol. Phys., 290, 1135

    2015

  8. [8]

    S., Upton, L

    Mahajan, S. S., Upton, L. A., Antia, H. M., et al. 2024, Sol. Phys., 299, 38

    2024

Show all 30 references
  1. [9]

    November, L. J. 1986, Appl. Opt., 25, 392

    1986

  2. [10]

    D., Thompson, B

    Pesnell, W. D., Thompson, B. J., & Chamberlin, P. C. 2012, Sol. Phys., 275, 3

    2012

  3. [11]

    2001, A&A, 377, L14

    Rieutord, M., Roudier, T., Ludwig, H.-G., Nordlund, Å., & Stein, R. 2001, A&A, 377, L14

    2001

  4. [12]

    2007, A&A, 471, 687

    Rieutord, M., Roudier, T., Roques, S., & Ducottet, C. 2007, A&A, 471, 687

    2007

  5. [13]

    A., & Rieutord, M

    Rincon, F., Roudier, T., Schekochihin, A. A., & Rieutord, M. 2017, A&A, 599, A69

    2017

  6. [14]

    M., Gelly, B., et al

    Roudier, T., Malherbe, J. M., Gelly, B., et al. 2020, A&A, 641, A50

    2020

  7. [15]

    M., Stein, R

    Roudier, T., Malherbe, J. M., Stein, R. F., & Frank, Z. 2019, A&A, 622, A112

    2019

  8. [16]

    M., et al

    Roudier, T., Rieutord, M., Malherbe, J. M., et al. 2012, A&A, 540, A88

    2012

  9. [17]

    M., & Vigneau, J

    Roudier, T., Rieutord, M., Malherbe, J. M., & Vigneau, J. 1999, A&A, 349, 301

    1999

  10. [18]

    2013, A&A, 552, A113

    Roudier, T., Rieutord, M., Prat, V ., et al. 2013, A&A, 552, A113

    2013

  11. [19]

    M., & Rieutord, M

    Roudier, T., Švanda, M., Ballot, J., Malherbe, J. M., & Rieutord, M. 2018, A&A, 611, A92

    2018

  12. [20]

    H., Schou, J., Bush, R

    Scherrer, P. H., Schou, J., Bush, R. I., et al. 2012, Sol. Phys., 275, 207

    2012

  13. [21]

    H., Bush, R

    Schou, J., Scherrer, P. H., Bush, R. I., et al. 2012, Sol. Phys., 275, 229

    2012

  14. [22]

    Stein, R. F. 2012, Living Reviews in Solar Physics, 9, 4

    2012

  15. [23]

    Stein, R. F. & Nordlund, Å. 1998, ApJ, 499, 914

    1998

  16. [24]

    F., Nordlund, Å., Georgoviani, D., Benson, D., & Schaffenberger, W

    Stein, R. F., Nordlund, Å., Georgoviani, D., Benson, D., & Schaffenberger, W. 2009, in Astronomical Society of the Pacific Conference Series, V ol. 416, Solar-Stellar Dynamos as Revealed by Helio- and Asteroseismology: GONG 2008/SOHO 21, ed. M. Dikpati, T. Arentoft, I. Gonzále...

    2009

  17. [25]

    Strous, L. H. 1994, PhD thesis, University of Utrecht, Netherlands

    1994

  18. [26]

    Strous, L. H. 1995, in ESA Special Publication, V ol. 376, Helioseismology, ed. J. T. Hoeksema, V . Domingo, B. Fleck, & B. Battrick, 213

    1995

  19. [27]

    2018, Sol

    Tremblay, B., Roudier, T., Rieutord, M., & Vincent, A. 2018, Sol. Phys., 293, 57

    2018

  20. [28]

    M., et al

    Upton, L., Mahajan, S., Antia, H. M., et al. 2024, in AGU Fall Meeting Abstracts, V ol. 2024, AGU Fall Meeting Abstracts, SH13A–2904

    2024

  21. [29]

    2018, Astronomische Nachrichten, 339, 268

    Verma, M., Kummerow, P., & Denker, C. 2018, Astronomische Nachrichten, 339, 268

    2018

  22. [30]

    2013, A&A, 555, A136 Article number, page 10 of 11 M

    Verma, M., Steffen, M., & Denker, C. 2013, A&A, 555, A136 Article number, page 10 of 11 M. Sampoorna et al.: Coherent Structure Tracking applied to solar Doppler maps Appendix A: LCC across the full-disk of a relatively less active Sun Fig. A.1.Pearson’s linear LCC for differe...

    2013

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