REVIEW 3 major objections 5 minor 3 references
On Polar Magnetic Field Reversal in Solar Cycles 21, 22, 23, and 24
T0 review · 3 major / 5 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read Polar-field precursor predicts a weak Solar Cycle 25, peaking at 116 ± 12
desk verdict A useful descriptive reversal chronology undermined by a polar-field forecast that the observed Cycle 25 has already contravened. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the maximum smoothed polar-field strength measured before a cycle minimum, an average magnetic flux over the latitude band from roughly ±55° to the pole. The paper treats this number as a precursor of the next cycle's activity maximum and fits a straight line, $Y = 1.466X + 22.141$, through the three available cycles (22, 23, and 24), where $X$ is the precursor field and $Y$ is the smoothed monthly sunspot maximum. Inserting the measured $X = 64$ μT before cycle 25 gives $116 \pm 12$. The reversal timings are constructed by reading when the polar-field curves cross zero in the near-polar zone and when the reversal completes at the poles; comparing those epochs with hemispheric sunspot maxima and heliospheric current-sheet tilts is how the paper establishes the north-first pattern and the 0.5 to 2.0 year zone-to-pole lag.
What would settle it
The decisive observation is the actual maximum smoothed monthly sunspot number of cycle 25: if it falls outside 116 ± 12, roughly 104 to 128, the paper's linear polar-field precursor calibration is contradicted.
Extended reading notes
Core claim
On the paper's own terms, the discovery is that the four most recent solar cycles share a clear reversal chronology: polarity reversal is completed first at the north pole and then at the south pole, with delays of 0.6, 1.1, 0.7, and 0.9 years for cycles 21, 22, 23, and 24. In the measured near-polar zone from about ±55° to the pole, the field crosses zero 0.5 to 2.0 years before the reversal is completed at the pole itself. Cycle 24 is distinctive because the northern polar field crossed zero three times, but the paper shows that multiple reversals are not unique to cycle 24. Using the maximum smoothed polar-field strength reached before each minimum as a precursor, the paper fits a linear relation to the three available cycles and predicts the maximum of cycle 25 at 116 ± 12 smoothed monthly sunspot numbers, essentially equal to cycle 24's 116.4.
Load-bearing premise
The forecast assumes that a straight-line relation between maximum smoothed polar-field strength and the following cycle's sunspot maximum, fitted to only three cycles, continues to hold for cycle 25.
Editorial extensions
If this is right
- If cycle 25 peaks at 116 ± 12, weak solar activity continues for another cycle, with amplitude close to cycle 24 rather than a return to stronger cycles.
- The north-first completion pattern holds in four consecutive cycles, making north-first reversal a reasonable expectation for future cycles unless a cycle with unusually strong southern activity breaks it.
- The 0.5 to 2.0 year delay between the near-polar zone crossing and completion at the pole offers a simple estimate of how long magnetic flux takes to reach the pole, serving as a high-latitude transport diagnostic.
- A single polar-field measurement near the minimum gives an early, cheap estimate of the next cycle's size, without requiring a full dynamo model.
- The triple reversal in cycle 24, placed alongside earlier examples, implies that single reversals are not a strict requirement of the reversal mechanism.
Reading between the lines
- I infer that the decisive test is sample size: with only three calibration cycles, the line's slope is effectively set by two points, so the prediction's uncertainty is larger than the quoted ±12 until a fourth cycle either validates or breaks the calibration.
- I infer that the paper's proposed link between cycle amplitude and the zone-to-pole lag could be extended backward in time using filament-based reversal timings from earlier cycles, providing a retrospective check on the relation.
- I infer that the same precursor method could be applied to reconstructed polar fields from historical minima, which would test whether the linear relation is stable across cycles of very different sizes.
- I infer that the triple-reversal interpretation points toward a modeling test: transport of active regions with non-standard polarity to the pole should reproduce repeated zero crossings, whereas ordinary transport should not.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper analyzes polar magnetic field polarity reversals in Solar Cycles 21-24 using Wilcox Solar Observatory measurements, filaments/prominences, hemispheric sunspot numbers, and HCS tilts. It reports a triple reversal in the N-hemisphere in Cycle 24, lists completion epochs in Table 1, and compares these with hemispheric activity and HCS tilt maxima. The final part of the paper uses the maximal smoothed WSO polar field before each cycle minimum as a precursor and fits a line to three cycles to forecast that Solar Cycle 25 will have amplitude 116 ± 12 in smoothed monthly sunspot numbers, comparable to Cycle 24.
Significance. If the reversal chronology were the only content, the paper would be a useful observational contribution: Table 1 organizes previously scattered reversal epochs, the Cycle 24 triple-reversal finding is documented, and the comparison with HCS tilts and hemispheric activity is a reasonable descriptive exercise. However, the headline claim is the Cycle 25 forecast, and that claim is both statistically fragile and now empirically contradicted: the observed smoothed monthly sunspot maximum of Cycle 25 is above the stated upper bound of 128 and is larger than the Cycle 24 amplitude of 116.4. The forecast is therefore not a minor blemish but the failure of the paper's central predictive assertion. The paper ships no code or machine-checked derivation; its falsifiable prediction has been made and falsified, so the significance of the work rests entirely on the descriptive parts.
major comments (3)
- [Section 3.5 and Abstract] The Cycle 25 forecast of 116 ± 12 is not statistically supported. The relation Y = 1.466X + 22.141 is a straight line drawn through the Cycle 22 and Cycle 24 points, with Cycle 23 the only independent check; the paper itself states that 'we cannot do any serious statistical studying.' The quoted uncertainty 12.1 appears without derivation: no residual scatter, prediction interval, or leave-one-out error is given. Moreover, the forecast has since been empirically falsified: the observed SILSO smoothed monthly sunspot number maximum of Cycle 25 lies above the interval's upper end of 128.1 and is substantially stronger than the Cycle 24 amplitude of 116.4. The central predictive claim of the paper therefore fails.
- [Table 1 and Section 3.1-3.4] The reversal epochs in Table 1 are given without uncertainties. The paper's quantitative conclusions, such as the ΔT values (0.6, 1.1, 0.7, 0.9 years) and the Section 4 inference that stronger cycles have faster high-latitude meridional flow, rely on differences of a few tenths of a year. Section 2 states that filament-based and magnetic-based reversal timings agree to one-two Carrington rotations, but the table entries are not accompanied by error bars or a formal uncertainty propagation. Without this, the chronological comparisons are underdetermined and the meridional-circulation argument in Section 4 is not supported.
- [Section 3.5, precursor choice] The precursor used for the forecast is the maximal smoothed WSO polar field before the cycle minimum, rather than the polar field strength at the minimum itself. The latter is the physically standard precursor reference (Schatten et al., 1978). The choice to use the pre-minimum maximum is not justified, and it has a direct effect on the fitted line in Figure 6: the '24' and '25' points (65 μT and 64 μT) are both taken from this pre-minimum maximum. A different, equally defensible definition of the precursor could change the regression and hence the predicted amplitude; this needs to be addressed if the forecast is to be considered robust.
minor comments (5)
- [Figure 6 caption] The caption calls the dashed line the 'best linear fit', but Section 3.5 states that the line connects the '24' and '22' points; the caption should say explicitly that it is a two-point line with Cycle 23 shown as a check, not a least-squares fit to all three points.
- [Section 2] The URL for SILSO is given as 'http://sidc.oma.be/SISLO', which appears to be a typo for 'SILSO'.
- [Section 2 and Figure 4] The rescaling of Temmer et al. (2002) hemispheric sunspot numbers by a factor of 1.5 is stated but not derived; a brief justification or reference would help readers assess the comparability of the two data sets.
- [References] Some reference entries contain typographical errors, for example 'act. id. 21' in the Mordvinov and Kitchatinov (2019) entry and 'e.q.' instead of 'e.g.' in Section 2; these should be corrected.
- [Abstract and Section 3.5] The phrase 'the current cycle amplitude equaled to 116.4' is ambiguous at the time of writing because the 'current cycle' is Cycle 24; this should be rephrased to 'the amplitude of Cycle 24'.
Circularity Check
No significant circularity: the reversal chronology rests on independent observations and the Cycle 25 forecast is an explicit empirical extrapolation, not a tautology.
full rationale
The paper has two main components. First, the reversal epochs for Cycles 21-23 are taken from the author's earlier paper (Pishkalo et al., 2005) and for Cycle 24 from Pishkalo and Leiko (2016). These are self-citations, but the paper states that those timings were derived from polar prominence/filament observations and averaged magnetic field measurements, and it explicitly compares them with independent results from Sun et al. (2015), Gopalswamy et al. (2016), and Janardhan et al. (2018). The cited data are external, observable, and not defined in terms of the conclusions drawn here, so this self-citation is not circular. Second, the Cycle 25 prediction in Section 3.5 uses the maximal smoothed WSO polar field strength (64 microtesla) as a precursor and inserts it into a linear relation Y = 1.466*X + 22.141 calibrated on Cycles 22 and 24, with Cycle 23 as a consistency check. The target quantity, the smoothed monthly sunspot number maximum, is an independent observable and is not defined in terms of the predictor. The predicted point is an extrapolation beyond the fitted data, not a fitted parameter renamed as a prediction. The paper candidly admits "we cannot do any serious statistical studying," meaning the forecast is statistically weak and may be empirically wrong, but that is a limitation, not circularity. No uniqueness theorem, ansatz-smuggling citation, or definitional equivalence is present. The claimed derivation does not reduce to its inputs by construction, so the circularity score is 0.
Assumptions & free parameters
free parameters (2)
- Slope of polar field to sunspot number regression =
1.466
- Intercept of polar field to sunspot number regression =
22.141
assumptions (4)
- domain assumption Polar field strength near cycle minimum is a physically based precursor for the next cycle's amplitude
- domain assumption Reversal completion times from filament and prominence disappearances (cycles 21-23) are directly comparable to magnetic-field-based completion times (cycle 24)
- domain assumption The WSO polar field measurement over the latitude range ±55-90 degrees is a sufficient proxy for polar field evolution
- ad hoc to paper The maximal smoothed WSO polar field before the minimum, rather than the value at the minimum itself, is the appropriate predictor
Cite this review
Pith. "Pith review of On Polar Magnetic Field Reversal in Solar Cycles 21, 22, 23, and 24." pith.science (2026). https://pith.science/paper/CIELVM72
@misc{pith2026190900055,
author = {Pith},
title = {Pith review of: On Polar Magnetic Field Reversal in Solar Cycles 21, 22, 23, and 24},
year = {2026},
howpublished = {\url{https://pith.science/paper/CIELVM72}},
note = {Machine review of arXiv:1909.00055}
}
read the original abstract
The Sun's polar magnetic fields change their polarity near the maximum of sunspot activity. We analyzed the polarity reversal epochs in Solar Cycles 21 to 24. There was a triple reversal in the N-hemisphere in Solar Cycle 24 and single reversals in the rest of cases. Epochs of the polarity reversal from measurements of the Wilcox Solar Observatory (WSO) are compared with ones when the reversals were completed in the N- and S-hemispheres. The reversal times were compared with hemispherical sunspot activity and with the Heliospheric Current Sheet (HCS) tilts, too. It was found that reversals occurred at the epoch of the sunspot activity maximum in Cycles 21 and 23, and after the corresponding maxima in Cycles 22 and 24, and one-two years after maximal HCS tilts calculated in WSO. Reversals in Solar Cycles 21, 22, 23, and 24 were completed first in the N-hemisphere and then in the S-hemisphere after 0.6, 1.1, 0.7, and 0.9 years, respectively. The polarity inversion in the near-polar latitude range \pm(55-90)^\circ occurred from 0.5 to 2.0 years earlier that the times when the reversals were completed in corresponding hemisphere. Using the maximal smoothed WSO polar field as precursor we estimated that amplitude of Solar Cycle 25 will reach 116 \pm 12 in values of smoothed monthly sunspot numbers and will be comparable with the current cycle amplitude equaled to 116.4.
Reference graph
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Reviewed August 14, 2026 · model on record in the stance chip above.
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