REVIEW 3 major objections 6 minor 49 references
The source of the 2017 cosmic ray half-year modulation event
T0 review · 3 major / 6 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read The paper argues that the half-year 2017 depression in galactic cosmic ray proton flux was produced by a sequence of solar wind interaction regions and coronal mass ejections, with four CMEs from one unusually active magnetic source doing…
desk verdict A plausible catalog-based explanation of the 2017 GCR depression, but the largest per-event decrease sits on a data gap and needs an explicit recomputation. 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 an event-by-event catalogue table (Table 1) that lists the arrival times at 1 AU of Carrington rotations, stream interaction regions, co-rotating interaction regions and coronal mass ejections during June to December 2017, with flare strength and active-region origin for each CME. The table is matched visually to the daily AMS-02 proton flux (Figure 6) and to Oulu neutron monitor data (Figure 7), so that each measured decrease is assigned to a listed structure. A second piece of machinery is the rigidity-resolved analysis: for the two strongest periods, the percentage decrease follows a power law in rigidity up to about 30 GV and then flattens, which is the paper's diagnostic that the modulation is solar rather than extra-heliospheric.
What would settle it
Check the in-situ spacecraft data at 1 AU for the times of the four largest flux drops: if there are no corresponding ICME shocks and magnetic ejecta, or if a heliospheric transport simulation including only the catalogued CIRs and SIRs reproduces the half-year depression without the four CMEs, the central claim would be contradicted.
Extended reading notes
Core claim
On the paper's own terms, the central discovery is that the half-year depression observed in AMS-02 galactic proton flux in the second half of 2017, which initially resembled a very long Forbush decrease, was caused by a combination of co-rotating interaction regions, stream interaction regions and coronal mass ejections, and was substantially enhanced by four strong CMEs from the same magnetic source. That source, labeled AR12665, AR12673 and AR12685 on different rotations, persisted for five Carrington rotations and produced the most active flaring of Solar Cycle 24, including the X9.3 flare of September 2017. Although there were minicycle-like rises in the heliospheric magnetic field magnitude and changes in the heliospheric current sheet tilt before the depression, the authors conclude that the depression itself cannot be attributed to a 1974-style minicycle because enhanced eruptive activity was co-temporal with it. The solar origin is supported by the rigidity dependence of the depression, which is strong below roughly 30 GV and weak above it.
Load-bearing premise
Each measured drop in proton flux is attributed to a catalogued CME, SIR, or CIR solely by aligning arrival times with dips in the flux time series by eye, with no transport model or statistical test to rule out coincidence or unlisted modulators.
Editorial extensions
If this is right
- The 2017 event should be counted as a solar-activity event, not a recurrence of the 1974 minicycle, so comparisons of solar-cycle minima should treat it differently.
- Long, half-year cosmic ray depressions near solar minimum can be produced by a sequence of CMEs and interaction regions from a persistent active region, without requiring a global dynamo change.
- Tracking a magnetic source as it crosses the disk over multiple rotations, as AR12665, AR12673 and AR12685 did, could provide early warning for similar prolonged cosmic ray depressions.
- Because the depression opposes the general rise of proton flux toward solar minimum, the same activity at another phase of the cycle would be less visible in the flux record.
Reading between the lines
- A control experiment the paper does not run: remove the four strong CMEs from a transport simulation and ask how much of the half-year depression remains; the paper's claim predicts a much weaker and shorter dip from CIRs and SIRs alone.
- The same matching method could be applied to AMS-02 helium, electron and positron fluxes for 2017 to test whether charge-sign dependent modulation supports the CME/IR attribution.
- The paper's closing remark implies that a broader notion of “minicycle” may still be needed to explain why the Sun produced its most active region of the cycle near minimum; that would connect the event to dynamo studies rather than purely to weather-like eruptions.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper investigates the cause of the half-year depressions observed in AMS-02 galactic cosmic ray proton fluxes during the second half of 2017. It compares two hypotheses: (1) a 'minicycle' produced by a global change in the solar magnetic field, of the type argued for the 1974 event, and (2) a combined effect of coronal mass ejections (CMEs), stream interaction regions (SIRs), and corotating interaction regions (CIRs). The authors first establish a solar origin from the rigidity dependence of the depression, then argue that minicycle-like signatures before the event are not accompanied by the absence of eruptive activity required by the 1974 definition. Using catalogued CME, SIR, and CIR arrival times, together with daily AMS-02 proton fluxes in low-rigidity bins and Oulu neutron monitor data, they attribute the depression to a sequence of recurrent CMEs and interaction regions, and conclude that the four largest impacts came from CMEs that all originated from a single persistent, unusually active magnetic source that they identify as AR12665, AR12673, and AR12685 in successive rotations.
Significance. If the conclusion holds, the paper resolves an important puzzle: the 2017 event is shown not to be a 1974-style minicycle but a sustained sequence of solar eruptive activity, with a single active complex as the dominant driver. The analysis is valuable because it brings together publicly available catalogues (Richardson & Cane, HELIO4CAST, STEREO, SolarMonitor) and independent datasets (AMS-02 and neutron monitors), and it makes a falsifiable claim about the role of a recurring active region. The paper does not rely on a fitted transport model, and the rigidity-dependent power-law forms in Figure 8 are presented as descriptive rather than as fitted parameters, which limits the risk of circularity. The main weaknesses are quantitative: several % decreases in Table 1 are read off by eye without uncertainties, and the largest attributed impact overlaps a known AMS-02 data gap. These issues, while locally fixable, currently weaken the quantitative support for the central claim that the depression was 'enhanced substantially' by the four identified CMEs.
major comments (3)
- [§3.2, Table 1 and Figure 6 caption] The 24.4% decrease attributed to the X9.3 CME (07-09 to 10-09 September, in the 1.0-1.16 GV bin) overlaps the 09-15 September data gap that the Figure 6 caption states exists for daily AMS-02 measurements below the 2.97-3.29 GV bin. The paper does not explain how this value was computed across the gap (e.g., by using the last pre-gap point, interpolation, or a higher rigidity bin). Since this event is one of the four CMEs identified as having the largest impacts, the quantitative attribution is load-bearing. Please state the exact method used and provide an uncertainty estimate, or replace the value with one derived from a rigidity bin that is not affected by the gap.
- [§3.2, Table 1 and §3.3, Figure 8] The % decreases in Table 1 are read from the daily flux by eye and are presented without uncertainties or significance tests, and the M5.5 CME (06-08 September) is listed with no % decrease, which makes the event-by-event decomposition in the same period ambiguous. A reproducible definition of the % decrease (e.g., baseline level minus local minimum, with a stated time window) and error bars from the AMS-02 flux uncertainties are needed so that the reader can judge whether the claimed effects exceed ordinary daily variability or overlap with adjacent SIR/CIR effects.
- [§3.2 and §4] The central conclusion that AR12665, AR12673, and AR12685 are manifestations of 'the same magnetic source' persisting for five Carrington rotations is asserted on the basis of labels and locations, but no quantitative tracking is provided (e.g., Carrington longitudes, magnetic-flux emergence histories, or coronal-hole connectivity). Because the uniqueness of this source is the paper's most distinctive claim, please present the supporting evidence in a table or figure; otherwise the statement that all four CMEs share a single source is an unsupported inference.
minor comments (6)
- [Throughout] The name is 'Bartels rotation', not 'Bartel rotation'; please correct this typo that appears in the abstract and body.
- [§3.1] In the sentence 'Carringtion rotations as the markers of CIR impact', 'Carringtion' should be 'Carrington'.
- [Abstract] The phrase 'co-rotating/stream interactions regions' should be 'co-rotating/stream interaction regions' (singular 'interaction').
- [§2.1, Figure 4 discussion] The sentence 'Further corroboration be found in Figure 4 (b)' is missing 'can'; it should read 'Further corroboration can be found in Figure 4 (b)'.
- [Figure 8] The power-law fits in panels (b) and (d) are useful as indicators of trends, but they are shown without uncertainties or goodness-of-fit statistics; please state that they are descriptive fits only, or add a brief caption note.
- [§3.2, Table 1 header] The LaTeX artifact 'T able 1' should be corrected to 'Table 1'.
Circularity Check
No significant circularity: the causal argument is built from external solar-wind and flare catalogues plus independent AMS-02 and neutron-monitor data, not from fitted parameters re-predicted as results.
full rationale
The paper does not fit a parameter to the AMS-02 flux and then re-predict the same flux; the % decreases in Table 1 are descriptive estimates read from Figure 6 for events whose arrival times are taken from independent catalogues (Richardson & Cane, HELIO4CAST, WIND/DREAMS, STEREO, Wilcox Solar Observatory, SolarMonitor). The minicycle hypothesis is tested against external B and HCS tilt data and rejected because co-temporal CME activity cannot be excluded, not because of a self-citation. The use of Carrington rotations as markers of CIR impact is an explicit observational convention, not an equation that makes the causal conclusion true by construction. The power-law fits in Figure 8 are descriptive trend indicators and are not used to predict the depression. Citations to the authors' own prior work appear only in forward-looking modelling plans and a cross-checking tool, so they are not load-bearing. The main weaknesses—the 09-15 September 2017 data gap overlapping the X9.3 CME interval and the absence of statistical significance tests for individual % decreases—are evidential or correctness concerns, not circularity. No derivation step reduces to its own input by definition or by self-citation.
Assumptions & free parameters
free parameters (1)
- Power-law fit coefficients for % decrease versus rigidity =
amplitudes 30.14, 7.14, 36.99, 9.22; exponents -0.86, -0.47, -0.76, -0.59
assumptions (5)
- standard math Least-squares power-law fitting is appropriate for the rigidity-dependence trends in Figure 8.
- domain assumption The public catalogues of CMEs, SIRs and CIRs are complete and accurate for the June to December 2017 period.
- domain assumption Each decline in the daily AMS-02 proton flux can be attributed to the nearest catalogued interplanetary structure.
- domain assumption The weakening of the depression above approximately 30 GV indicates a solar/heliospheric origin.
- domain assumption Active region labels AR12665, AR12673 and AR12685 correspond to the same persistent magnetic source over five solar rotations.
invented entities (1)
-
Single persistent magnetic source behind AR12665, AR12673 and AR12685
Cite this review
Pith. "Pith review of The source of the 2017 cosmic ray half-year modulation event." pith.science (2026). https://pith.science/paper/UM2ARY7V
@misc{pith2026241214907,
author = {Pith},
title = {Pith review of: The source of the 2017 cosmic ray half-year modulation event},
year = {2026},
howpublished = {\url{https://pith.science/paper/UM2ARY7V}},
note = {Machine review of arXiv:2412.14907}
}
read the original abstract
In 2017, as the solar cycle approached solar minimum, an unusually long and large depression was observed in galactic cosmic ray (GCR) protons, detected with the Alpha Magnetic Spectrometer (AMS-02), lasting for the second half of that year. The depression, as seen in the Bartel rotation-averaged proton flux, has the form of a Forbush decrease (FD). Despite this resemblance, however, the cause of the observed depression does not have such a simple explanation as FDs, due to coronal mass ejections (CMEs), typically last for a few days at 1 AU rather than half a year. In this work, we seek the cause of the observed depression and investigate two main possibilities. First, we consider a mini-cycle - a temporary change in the solar dynamo that changes the behavior of the global solar magnetic field and, by this, the modulation of GCRs. Secondly, we investigate the behavior of solar activity, both CMEs and co-rotating/stream interactions regions (C/SIRs), during this period. Our findings show that, although there is some evidence for mini-cycle behavior prior to the depression, the depression is ultimately due to a combination of recurrent CMEs, SIRs and CIRs. A particular characteristic of the depression is that the largest impacts that help to create and maintain it are due to four CMEs from the same, highly active, magnetic source that persists for several solar rotations. This active magnetic source is unusual given the closeness of the solar cycle to solar minimum, which also helps to make the depression more evident.
Figures
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Reference graph
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Reviewed August 11, 2026 · model on record in the stance chip above.
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