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arxiv: 2606.06703 · v1 · pith:HFXD7ZOTnew · submitted 2026-06-04 · 🌌 astro-ph.SR

Oscillatory Phase and Acoustic Travel-Time Inconsistencies Measured between SDO/HMI and GONG Dopplergrams

Junwei Zhao , Ruizhu Chen , S. P. Rajaguru , Shukur Kholikov This is my paper

Pith reviewed 2026-06-27 23:16 UTC · model grok-4.3

classification 🌌 astro-ph.SR
keywords helioseismologymeridional circulationphase shiftsacoustic travel timesSDO/HMIGONGDopplergramsinstrument artifacts
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The pith

Both SDO/HMI and GONG Dopplergrams exhibit growing phase-shift anomalies and east-west travel-time inconsistencies indicating systematic artifacts.

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

The paper compares contemporaneous Dopplergrams from SDO/HMI and GONG that have been processed identically to locate sources of discrepancy in meridional-circulation measurements. It identifies a persistent phase-shift anomaly in the northwestern solar disk whose size increases from 2010 through 2024. After the axisymmetric part is removed, the remaining maps display a northeast-to-southwest trend that could be misread as flows. North-south acoustic travel times also disagree between the eastern and western sides of the central meridian in both instruments, contrary to expectation. The results indicate that both instruments carry systematic artifacts that affect flow measurements.

Core claim

Using consistently processed contemporaneous Dopplergrams, relative oscillatory phase shifts at identical solar locations reveal a persistent area of phase-shift anomalies in the northwestern quadrant whose magnitude increases over the analysis period from 2010 through 2024. After removing the axisymmetric component, the phase-shift maps display a decreasing trend from the northeastern to the southwestern quadrant. The travel-time measurements also show significant inconsistencies on the eastern and western sides of the central meridian for both instruments, although close agreement between both sides is expected.

What carries the argument

Measurement of relative oscillatory phase shifts at identical solar locations together with north-south acoustic travel-time shifts on both sides of the solar central meridian.

If this is right

  • Both SDO/HMI and GONG carry systematic artifacts affecting meridional-circulation measurements.
  • Time-varying phase anomalies and eastern-western asymmetry pose major challenges for accurate characterization and correction.
  • The inconsistencies persist across the full interval from 2010 through 2024.
  • Axisymmetric removal still leaves a quadrant trend that can be misinterpreted as flows.

Where Pith is reading between the lines

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

  • Cross-instrument comparisons may help separate real solar signals from artifacts in existing meridional-flow maps.
  • Dynamo models that ingest these flow measurements could inherit systematic quadrant biases.
  • New processing steps targeting the northwestern anomaly region might reduce the observed discrepancies.
  • Similar phase and travel-time diagnostics could be applied to other helioseismic observables to check consistency.

Load-bearing premise

Identical processing of contemporaneous Dopplergrams fully removes all non-instrumental differences so that remaining discrepancies must originate in the instruments rather than in unmodeled solar variability.

What would settle it

A third independent Dopplergram source or a revised calibration that eliminates the northwestern phase anomaly and the east-west travel-time asymmetry while preserving agreement between instruments would test the claim.

Figures

Figures reproduced from arXiv: 2606.06703 by Junwei Zhao, Ruizhu Chen, Shukur Kholikov, S. P. Rajaguru.

Figure 1
Figure 1. Figure 1: Sample Dopplergrams from SDO/HMI (left) and GONG (right) after the data are remapped to Postel’s projection. allow for appropriate and more accurate corrections in future analyses. In this paper, we analyze contemporaneous Dopplergrams from SDO/HMI and GONG to investigate this systematic discrepancy through comparing the disk-location￾dependent oscillatory phases and the measured acoustic travel times. Sec… view at source ↗
Figure 2
Figure 2. Figure 2: Simultaneous time sequences obtained by SDO/HMI (dark) and GONG (red) at the same disk location that is randomly selected. 60 seconds, which we retain without interpolating them to match the SDO/HMI cadence [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Map of relative phase shifts δϕ(r) between SDO/HMI and GONG Dopplergrams, obtained between the frequency of 3.0 − 4.0 mHz for 2018 January. Note that the values are saturated near the limbs, but these areas are typically out of our interest in making meridional circulation measurements. The dark box indicates the location of the major phase anomalies, inside which the values are averaged for the temporal e… view at source ↗
Figure 4
Figure 4. Figure 4: Map of relative phase shifts δϕ(r) between SDO/HMI and GONG Dopplergrams, obtained for 2018 January for the frequency range of 2.0−3.0, 3.0−4.0, 4.0−5.0, 5.0−6.0, and 6.0 − 7.0 mHz, respectively. Note that the values are saturated near the limbs for all panels. SOLA: main.tex; 8 June 2026; 0:11; p. 6 [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Map of relative phase shifts δϕ(r) between SDO/HMI and GONG Dopplergrams, obtained for selected months of selected years, with an intention to cover the analyzed data period and different months of the year. Note that the values are saturated near the limbs for all panels [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: (a) Temporal evolution of the phase anomalies measured between the SDO/HMI and GONG Dopplergrams, averaged over the area indicated by the box in [PITH_FULL_IMAGE:figures/full_fig_p008_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: (a) Phase-shift map between SDO/HMI and GONG Dopplergrams averaged be￾tween 3.0 − 4.0 mHz throughout the entire analysis period of 14 years, displayed after an azimuthally-averaged CtoL variation is removed. (b) Map of standard errors corresponding to phase-shift map shown in (a), estimated from monthly measurements throughout the 14-year span. (c) Phase shifts averaged in the latitudinal bands of 30◦S – 2… view at source ↗
Figure 8
Figure 8. Figure 8: (a) Acoustic travel-time shifts, δτ(∆, λ), measured along the Sun’s North-South direction using SDO/HMI data for the period of 2010.05.01 – 2024.04.30, and displayed as a function of measurement distance ∆ (corresponding to measurement depth) and latitude λ. The travel-time shifts include both the helioseismic CtoL effect and the meridional-circulation-in￾duced shifts, without the former subtracted. (b) Sa… view at source ↗
Figure 9
Figure 9. Figure 9: (a) Travel-time shifts, δτ(∆, λ), measured using SDO/HMI data on the eastern side of the central meridian. (b) The δτ(∆, λ) measured using SDO/HMI data on the western side the central meridian. (c) The δτ(∆, λ) measured using GONG data on the eastern side of the central meridian. (d) The δτ(∆, λ) measured using GONG data on the western side of the central meridian. with earlier reports (Gizon et al., 2020)… view at source ↗
Figure 10
Figure 10. Figure 10: (a) Comparison of travel-time shifts δτ measured using SDO/HMI data on the eastern and western sides of the central meridian, after the shifts are averaged over the latitudinal band of 20◦S – 20◦N. (b) Same as panel (a), but obtained from using GONG data [PITH_FULL_IMAGE:figures/full_fig_p013_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: (a) Comparison of travel-time shifts δτ measured using SDO/HMI and GONG data on the eastern side of the central meridian, after the shifts are averaged over the latitudinal band of 20◦S – 20◦N. (b) Same as panel (a) but for the measurements on the west side of the central meridian. from both sides of the central meridian should adequately represent the Sun’s meridional circulation. However, our results in… view at source ↗
Figure 12
Figure 12. Figure 12: (a) Temporal evolution of the eastern-western travel-time asymmetry measured from SDO/HMI and GONG Dopplergrams separately. (b) Temporal evolution of the trav￾el-time differences between SDO/HMI and GONG measurements, displayed separately for the eastern and western side of the central meridian. Sizes of typical measurement errors are illustrated in the legend area of each panel. substantial differences c… view at source ↗
read the original abstract

We investigate the causes of discrepancies in meridional-circulation measurements derived from the helioseismic observations by the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory (SDO/HMI) and the Global Oscillation Network Group (GONG). Using contemporaneous Dopplergrams from both instruments that are processed consistently, we measure relative oscillatory phase shifts at identical solar locations and analyze north-south acoustic travel-time shifts on both sides of the solar central meridian. Our analysis reveals a persistent area of phase-shift anomalies in the northwestern quadrant of the solar disk, whose magnitude increases over the analysis period from 2010 through 2024. After removing the axisymmetric component, the phase-shift maps display a deceasing trend from the northeastern to the southwestern quadrant, which can be misinterpreted as flows in helioseismic analyses. The travel-time measurements also show significant inconsistencies on the eastern and western sides of the central meridian for both instruments, although a close agreement between both sides is expected. These findings indicate that both SDO/HMI and GONG carry systematic artifacts affecting meridional-circulation measurements, and that the time-varying phase anomalies and eastern-western asymmetry pose major challenges for their accurate characterization and correction.

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

2 major / 2 minor

Summary. The paper claims that identical processing of contemporaneous Dopplergrams from SDO/HMI and GONG reveals persistent phase-shift anomalies in the northwestern solar quadrant (increasing 2010–2024), a decreasing NE-to-SW trend after axisymmetric removal, and east-west acoustic travel-time inconsistencies on either side of the central meridian. These are interpreted as evidence of systematic instrumental artifacts in both datasets that affect meridional-circulation inferences.

Significance. If the attribution to instrumental artifacts holds after proper validation, the result would be significant for helioseismology because it directly compares two widely used independent datasets and flags time-varying biases that could compromise meridional-flow measurements. The observational nature of the comparison (no free parameters or fitted models) is a methodological strength.

major comments (2)
  1. [Abstract] Abstract: the attribution of all remaining discrepancies to instrumental artifacts rests on the unvalidated premise that identical processing fully removes non-instrumental differences (solar variability, residual calibration); no forward-modeling tests or comparisons to simulated Dopplergrams with known flows are described to support this.
  2. [Abstract] Abstract: the reported phase anomalies and travel-time inconsistencies are presented without error bars, statistical significance tests, or any description of the extraction methods for phase and travel times, so the load-bearing claim that these features are real and instrument-specific cannot be assessed from the given information.
minor comments (2)
  1. [Abstract] Abstract: 'deceasing trend' is a typographical error and should read 'decreasing trend'.
  2. [Abstract] Abstract: the sentence 'although a close agreement between both sides is expected' is grammatically awkward and could be rephrased for clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive report. We address each major comment below, indicating where revisions to the manuscript will be made to strengthen the presentation.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the attribution of all remaining discrepancies to instrumental artifacts rests on the unvalidated premise that identical processing fully removes non-instrumental differences (solar variability, residual calibration); no forward-modeling tests or comparisons to simulated Dopplergrams with known flows are described to support this.

    Authors: We agree that forward-modeling with simulated Dopplergrams containing known flows would provide stronger validation of the instrumental interpretation. Our current approach relies on the direct, parameter-free comparison of two independent datasets processed identically, which reveals the same time-varying anomalies in both; such consistency is difficult to attribute to solar variability or residual calibration. We will add an explicit discussion of this limitation and the rationale for our interpretation in a revised discussion section. revision: yes

  2. Referee: [Abstract] Abstract: the reported phase anomalies and travel-time inconsistencies are presented without error bars, statistical significance tests, or any description of the extraction methods for phase and travel times, so the load-bearing claim that these features are real and instrument-specific cannot be assessed from the given information.

    Authors: The full manuscript contains the extraction methods in Section 2 and quantitative measures of the anomalies, but we acknowledge that the abstract lacks error bars, significance tests, and a concise methods summary. We will revise the abstract to include these elements so that the strength of the claims can be evaluated directly from it. revision: yes

Circularity Check

0 steps flagged

No circularity: pure observational comparison of two independent datasets

full rationale

The paper performs direct measurements of phase shifts and travel times on contemporaneous Dopplergrams from HMI and GONG after consistent processing. No equations, fitted parameters, or derivations are presented that reduce reported discrepancies to prior results or self-citations. The central claims rest on empirical differences between the two instruments rather than any self-referential construction. This matches the default expectation of no significant circularity for observational comparisons.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Observational data-comparison study; no mathematical model, free parameters, or new physical entities are introduced.

pith-pipeline@v0.9.1-grok · 5758 in / 1061 out tokens · 20463 ms · 2026-06-27T23:16:36.586954+00:00 · methodology

discussion (0)

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Reference graph

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