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Deriving the solar activity cycle modulation on cosmic ray intensity observed by Nagoya muon detector from October 1970 until December 2012

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Pith's one-line read A corrected 42-year Nagoya muon detector record displays the 11 and 22 year solar cycle modulation, with high correlation to neutron monitor and anti-correlation to sunspot number.

arxiv 1908.00395 v1 pith:GKRKZY3U submitted 2019-08-01 physics.space-ph

Rafael R. S. de Mendonça , Carlos R. Braga , Ezequiel Echer , Alisson Dal Lago , Marlos Rockenbach , Nelson J. Schuch , Kazuoki Munakata This is my paper · ORCID
classification physics.space-ph
keywords intensitymuonobservedanalysischangescosmiccycledetector
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

Muon detectors on the ground record secondary particles from cosmic rays. But the observed count rate is affected by two problems: atmospheric temperature changes, which make muons decay before reaching the detector, and detector electronics problems or gaps. These effects make it hard to see the long-term 11-year cycle in the cosmic ray flux.

The authors cleaned 42 years of hourly data from the Nagoya detector. They flagged periods where the detector changed, and adjusted the count level using the Nagoya data itself. They also removed the temperature effect using a mass weighted method from an earlier paper, which uses the full atmospheric temperature profile. After these corrections, the Nagoya muon data track the McMurdo neutron monitor well and show the 11-year solar cycle pattern.

They report a correlation of 0.953 with the neutron monitor and an anti-correlation of -0.746 with the sunspot number. This is a preliminary result; the detailed analysis of the anti-correlation is left to a future paper. The corrected data might be useful for space weather and solar-terrestrial studies, but the paper does not release the data or code.

Extended reading notes

Core claim

The paper claims that 'a clear 11 and 22 years variations have been clearly observed in a good correlation (R = 0.953) with the cosmic ray intensity observed by the McMurdo Neutron Monitor' in the Nagoya muon VDC data after removing non-natural detector changes and the temperature effect (Section 3). If correct, this means a 42-year corrected muon detector record exhibits the known solar modulation with high fidelity.

Load-bearing premise

The largest unvalidated premise is that the monotonic intensity decrease from 1970 to 1974 is a detector efficiency loss, not a real cosmic ray modulation: 'We believe that the huge intensity decrease ... is related to an initial efficiency detection decrease, since there are no known natural phenomena that can produce this monotonous decrease' (Section 2, Fig. 2). If this decrease is natural, subtracting it would bias the long-term trend and the derived modulation amplitude.

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Assumptions & free parameters 2 free parameters · 3 assumptions · 0 invented entities

The central product is an empirical data record, so the main 'free parameters' are the data-cleaning coefficients and the temperature coefficient. No new physical entities are introduced.

free parameters (2)
  • Discontinuity correction coefficients (per detected event) = not reported
    The authors state that coefficients used for correcting discontinuities and gaps are calculated using NGY data only (Section 2); individual values are not given.
  • Mass-weighted temperature coefficient = -0.255 %/K
    Obtained using GDAS atmospheric data and the method of Mendonça et al. (2016); it is a model-derived coefficient, not fit to the muon intensity here, but its uncertainty affects the corrected series.
assumptions (3)
  • domain assumption Mass-weighted method correctly removes the atmospheric temperature effect on muon intensity at ground.
    The paper adopts this from prior work (Sagisaka 1986; Mendonça et al. 2016) without local validation against an independent measurement of the temperature effect.
  • ad hoc to paper The 1970-1974 monotonic decrease is caused by detector efficiency loss, not by natural phenomena.
    Stated as a belief in Section 2 based on the absence of known natural explanations; this correction determines the early part of the 42-year trend.
  • domain assumption Comparisons with McMurdo neutron monitor, Dst index, and ACE data are sufficient ground truth to distinguish natural from instrumental changes.
    The authors use these external data to decide when to adjust NGY data (Section 2), but the criteria for 'sufficient similarity' are not quantified.

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Pith. "Pith review of Deriving the solar activity cycle modulation on cosmic ray intensity observed by Nagoya muon detector from October 1970 until December 2012." pith.science (2026). https://pith.science/paper/GKRKZY3U

@misc{pith2026190800395,
  author       = {Pith},
  title        = {Pith review of: Deriving the solar activity cycle modulation on cosmic ray intensity observed by Nagoya muon detector from October 1970 until December 2012},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/GKRKZY3U}},
  note         = {Machine review of arXiv:1908.00395}
}
read the original abstract

It is well known that the cosmic ray intensity observed at the Earth's surface presents an 11 and 22-yr variations associated with the solar activity cycle. However, the observation and analysis of this modulation through ground muon detectors data is make difficult due to the temperature effect. Furthermore, detector electronic changes or temporary problems may difficult the analysis of these variations. In this work, we analyze the cosmic ray intensity observed since October 1970 until December 2012 by the Nagoya muon detector. We show the results obtained after analyzing all discontinuities and gaps present in this data and removing changes not related to natural phenomena. We also show the results found using the mass weighted method for eliminate the influence of atmospheric temperature changes on muon intensity observed at ground. Furthermore, we show the preliminary results of the analysis of the solar cycle modulation on the muon intensity observed for more than 40 years.

Figures

Figures reproduced from arXiv: 1908.00395 by the authors.

Figure 1
Figure 1. Examples of discontinuities and gaps found on the original hourly Nagoya (NGY) detector Vertical Directional Channel (VDC) Cosmic Ray Intensity Corrected by Pressure effect (CRI-CP).The black curve shows the NGY data, while the red curve represents the McMurdo neutron monitor data multiplied by 0.5. The top panel of [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Hourly Nagoya Vertical Directional Channel Cosmic Ray IntensityCorrected by Pres￾sure before and after solving data problems (black curves). The vertical light blue lines in the top panel indicate the periods when we notice non-natural changes in CRI-CP. The yellow slanted line in the top panel highlights the period when we assumed a detection efficiency decrease. The red and green curves in bottom panel show the 6 … view at source ↗
Figure 3
Figure 3. Hourly and Monthly NGY VDC cosmic ray intensity after solving electronic data problems and eliminating the temperature effect (black curve). The green curve shows the monthly average McMurdo neutron monitor data multiplied by 0.25. The red curve shows the monthly mean of NGY data. The purple curve represents the Monthly SWO Sunspot number. 3. Summary and Final Remarks After eliminating non-natural changes present in… view at source ↗

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Works this paper leans on

6 extracted references · 6 canonical work pages

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