Sub-surface structural changes associated with successive 11-yr solar activity cycles have been progressively more confined near the surface: new helioseismic results on Cycles 22 -- 25 from BiSON

Eleanor Murray; Rachel Howe; Sarbani Basu; Steven J. Hale; William J. Chaplin; Yvonne Elsworth

Frequency shifts in Cycle 25 show solar structural changes are becoming confined nearer the surface.

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2026-06-29 05:45 UTC pith:7YFLMX63

load-bearing objection Cycle 25 BiSON data show high-frequency mode shifts exceeding the Cycle 22 proxy relation, but the progressive near-surface confinement claim rests on treating that earlier relation as a stable deeper baseline. the 1 major comments →

arxiv 2605.29528 v1 pith:7YFLMX63 submitted 2026-05-28 astro-ph.SR astro-ph.EP

Sub-surface structural changes associated with successive 11-yr solar activity cycles have been progressively more confined near the surface: new helioseismic results on Cycles 22 -- 25 from BiSON

William J. Chaplin , Sarbani Basu , Rachel Howe , Yvonne Elsworth , Steven J. Hale , Eleanor Murray This is my paper

classification astro-ph.SR astro-ph.EP

keywords helioseismologysolar p-modesfrequency shiftssolar cyclesactivity proxiessub-surface structureBiSON

verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

BiSON Sun-as-a-star observations track frequency shifts of low-angular-degree p modes across solar cycles 22 to 25 and compare them to standard activity proxies. Higher-frequency modes exhibit much larger shifts in Cycle 25 than the earlier-cycle relationship would predict, while Cycle 25 appears weaker in the proxies themselves. Mid-frequency modes have shown steadily declining sensitivity to activity over the last three cycles. Together these patterns indicate that the subsurface perturbations tied to each 11-year cycle are occurring in a progressively thinner layer just below the surface. A reader would care because this evolution could change how the solar dynamo operates and how future activity is forecast.

Core claim

The observed mean frequency shifts in Cycle 25 are much stronger than one would expect for these modes based on the relationship between the frequencies and proxies seen in previous cycles, in particular Cycle 22. In sum, Cycle 25 is as strong as Cycles 22 and 23 when observed in this higher-frequency seismic band, in marked contrast to the relative sizes of the cycles seen in the global activity proxies, where Cycle 25 is noticeably weaker. When considered alongside a systematic reduction of the sensitivity of the mid-frequency modes to activity over the past three cycles, these results suggest that sub-surface structural changes associated with successive 11-year cycles are becoming ever m

What carries the argument

The comparison of p-mode frequency shifts in separate frequency bands against activity proxies across four solar cycles, using whole-Sun helioseismic data.

Load-bearing premise

The relationship between frequency shifts and activity proxies observed in earlier cycles provides a valid baseline for interpreting deviations in Cycle 25 as signs of changing subsurface structure.

What would settle it

Measurements from Cycle 26 that show high-frequency shifts matching the weakened activity-proxy strength without excess deviation would falsify the progressive-confinement interpretation.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

Cycle 25 matches the strength of Cycles 22 and 23 in the higher-frequency seismic band despite weaker global proxies.
The altered behavior between low-frequency modes and proxies that began on the decline of Cycle 23 persists through Cycle 25.
Mid-frequency mode sensitivity to activity has declined systematically over the past three cycles.
Subsurface structural changes tied to the magnetic cycle are occurring in a thinner near-surface layer with each successive cycle.

Where Pith is reading between the lines

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

Continued monitoring could test whether the confinement trend persists or reverses in Cycle 26.
Comparison with resolved-Sun helioseismic data from other instruments would check whether the pattern holds across different mode degrees.
Dynamo models may need to incorporate cycle-dependent changes in the depth at which magnetic perturbations affect sound speed.

Editorial analysis

A structured set of objections, weighed in public.

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

Desk Editor's Note

Cycle 25 BiSON data show high-frequency mode shifts exceeding the Cycle 22 proxy relation, but the progressive near-surface confinement claim rests on treating that earlier relation as a stable deeper baseline.

read the letter

The new result here is the Cycle 25 extension of the BiSON frequency-shift analysis. High-frequency modes now exhibit shifts that are stronger than the Cycle 22 relation predicts, while mid-frequency sensitivity has dropped over Cycles 23-25. This contrast with the weaker Cycle 25 seen in standard activity proxies is the concrete observation.

The work benefits from a single long-running instrument network, which reduces some cross-calibration issues when comparing cycles. The direct comparison of shifts to proxies across four cycles is clear and shows the pattern the authors highlight.

The soft spot is the depth interpretation. The claim that structural changes are becoming progressively confined near the surface assumes the Cycle 22 shift-proxy mapping represents the reference deeper response. Deviations in later cycles are then read as evidence of shallower perturbations. The stress-test point is fair: if the mapping itself varies across cycles for reasons unrelated to depth—such as changes in magnetic filling factor or how proxies sample the field—the attribution to confinement weakens. The abstract notes the change began on the declining phase of Cycle 23, so anchoring the baseline solely at Cycle 22 leaves open whether the trend is fully progressive or partly tied to the choice of reference.

This paper is for solar physicists tracking cycle-to-cycle variations in helioseismic data and their implications for dynamo models. It deserves peer review because the Cycle 25 observations are new and falsifiable against future data, even though the interpretive step needs closer examination of the assumptions.

Referee Report

1 major / 0 minor

Summary. The manuscript analyzes BiSON Sun-as-a-star helioseismology data on frequency shifts of low-degree p-modes relative to global solar activity proxies over Cycles 22–25. It reports persistence of changes first noted on the declining phase of Cycle 23, with higher-frequency modes in Cycle 25 exhibiting larger shifts than predicted from the Cycle 22 relation and mid-frequency modes showing systematically reduced sensitivity; these observations are interpreted as evidence that sub-surface structural perturbations associated with the 11-year cycle are becoming progressively more confined near the surface.

Significance. If substantiated, the result would indicate secular evolution in the depth distribution of cycle-related structural changes, with direct implications for solar dynamo models and the interpretation of activity proxies. The long, homogeneous BiSON time series is a clear asset for such cycle-to-cycle comparisons.

major comments (1)

[Abstract] Abstract: The inference of progressive near-surface confinement rests on treating the Cycle 22 frequency-shift versus proxy relation as the reference for a deeper structural response. The manuscript must show that this mapping is stable across cycles and not modulated by cycle-specific factors (e.g., changes in magnetic filling factor or how global proxies sample the relevant field) that could produce the observed deviations without any change in perturbation depth; the abstract’s statement that the change began on the declining phase of Cycle 23 makes the exclusive use of Cycle 22 as baseline a load-bearing assumption requiring explicit justification or robustness tests.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading and constructive feedback. We address the major comment below.

read point-by-point responses

Referee: [Abstract] Abstract: The inference of progressive near-surface confinement rests on treating the Cycle 22 frequency-shift versus proxy relation as the reference for a deeper structural response. The manuscript must show that this mapping is stable across cycles and not modulated by cycle-specific factors (e.g., changes in magnetic filling factor or how global proxies sample the relevant field) that could produce the observed deviations without any change in perturbation depth; the abstract’s statement that the change began on the declining phase of Cycle 23 makes the exclusive use of Cycle 22 as baseline a load-bearing assumption requiring explicit justification or robustness tests.

Authors: We agree that the choice of Cycle 22 as reference requires explicit justification. Cycle 22 provides the earliest complete coverage in the BiSON dataset and serves as the baseline established in our prior work (cited in the manuscript), where deviations were first identified on the declining phase of Cycle 23. We will revise the manuscript to include additional robustness tests comparing the frequency-shift versus proxy relations across Cycles 22–24, demonstrating stability of the mapping prior to the noted changes. While direct constraints on cycle-specific factors such as magnetic filling factor are not available from Sun-as-a-star observations, the use of multiple independent proxies (detailed in the manuscript) reduces the likelihood that proxy sampling alone explains the Cycle 25 deviations. We will update the abstract and add a dedicated discussion section to clarify these points. revision: yes

Circularity Check

0 steps flagged

No significant circularity in derivation chain

full rationale

The paper compares BiSON helioseismic frequency shifts directly to independent external activity proxies across cycles, with the Cycle 25 high-frequency mode deviations presented as new observational results relative to prior cycles. The single reference to a previous study (by overlapping authors) concerns only the onset of low-frequency changes in Cycle 23 and is not used to justify or derive the central Cycle 25 claim or the inferred depth confinement. No equations, fitted parameters, or self-citations are shown that reduce any prediction to the inputs by construction; the analysis remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Review based on abstract only; no explicit free parameters, axioms, or invented entities stated.

pith-pipeline@v0.9.1-grok · 5802 in / 997 out tokens · 19817 ms · 2026-06-29T05:45:46.578341+00:00 · methodology

0 comments

read the original abstract

We use Sun-as-a-star helioseismology data, collected by the Birmingham Solar-Oscillations Network (BiSON), to examine the relationship between the solar-cycle-induced frequency shifts of whole-Sun, low-angular degree solar p modes and well-known proxies of global solar activity. Changes in behaviour between the low-frequency modes and proxies, which in a previous study we found had occurred on the declining phase of Cycle 23, appear to have persisted into Cycle 25. More striking is a significant change in the relationship for higher-frequency modes, which the new Cycle 25 data now reveal. The observed mean frequency shifts in Cycle 25 are much stronger than one would expect for these modes based on the relationship between the frequencies and proxies seen in previous cycles, in particular Cycle 22. In sum, Cycle 25 is as strong as Cycles 22 and 23 when observed in this higher-frequency seismic band, in marked contrast to the relative sizes of the cycles seen in the global activity proxies, where Cycle 25 is noticeably weaker. When considered alongside a systematic reduction of the sensitivity of the mid-frequency modes to activity over the past three cycles, these results suggest that sub-surface structural changes associated with successive 11-year cycles are becoming ever more progressively confined just beneath the solar surface.

Figures

Figures reproduced from arXiv: 2605.29528 by Eleanor Murray, Rachel Howe, Sarbani Basu, Steven J. Hale, William J. Chaplin, Yvonne Elsworth.

**Figure 1.** Figure 1: Points with error bars: mean frequency shifts for each of the overlapping 1-yr segments in three different frequency bands, covering low (bottom panel), mid (middle panel) and high (top panel) ranges. Solid orange and dashed black lines: 1-yr averages of the 10.7-cm radio flux and SSN, respectively, scaled for the plots in each panel by a linear fit to the appropriate band frequency shifts in Cycle 22 [PI… view at source ↗

**Figure 2.** Figure 2: Mean frequency shifts and activity proxies for each of the overlapping 1-yr segments, as per [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗

discussion (0)

Reference graph

Works this paper leans on

4 extracted references

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@esa (Ref

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