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REVIEW 4 major objections 3 minor 1 cited by

The largest Forbush decrease in 20 years: Preliminary analysis of SEVAN network observations

T0 review · 4 major / 3 minor · reviewed 2026-08-06 · deepseek-v4-flash

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Pith's one-line read The SEVAN network observed the deepest Forbush decrease in 20 years, triggered by back-to-back Earth-directed coronal mass ejections on May 30-31, 2025, with two distinct minima and a week-long recovery.

desk verdict Useful first look at the June 2025 Forbush decrease from SEVAN, but the 'largest in 20 years' claim is not backed by the evidence presented. read the letter →

arxiv 2506.17917 v1 pith:YIJBISSQ submitted 2025-06-22 astro-ph.SR physics.ao-phphysics.space-ph

A. Chilingarian , T.Karapetyan , B.Sargsyan This is my paper · ORCID
classification astro-ph.SRphysics.ao-phphysics.space-ph
keywords ForbushdecreaseSEVANnetworkcosmicrayscoronalmassejectionsolarcycle25neutronmonitormuondetectorspaceweather
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

The paper reports the deepest Forbush decrease in two decades as seen by the SEVAN network, a set of mountain-top particle detectors in Armenia and Europe. It claims the event was triggered by two consecutive Earth-directed coronal mass ejections on May 30 and 31, 2025, whose interplanetary shocks arrived at Earth on June 1 and June 2 and produced two distinct minima in cosmic-ray flux. A prolonged recovery lasting nearly a week and a clear European-Aragats anisotropy are presented as evidence of the compound, structured nature of the interplanetary disturbance. If the record claim holds, the event becomes a benchmark for solar cycle 25 and a test case for how energy-differentiated muon and neutron measurements disentangle heliospheric modulation from magnetospheric effects.

What carries the argument

The central object is the SEVAN network, the Space Environment Viewing and Analysis Network, a chain of hybrid particle detectors at mountain altitudes in Armenia and Europe that records neutrons and muons, together with the STAND3 stacked detector that separates muons by energy threshold and the Aragats and Nor Amberd neutron monitors. The argument works by comparing energy-differentiated responses: neutrons originating from roughly 1-20 GeV primaries show the strongest Forbush-decrease signal because that is where heliospheric modulation is strongest, while muons with higher-energy primaries respond to both heliospheric modulation and local geomagnetic cutoff changes. This energy ladder lets the authors attribute the two FD minima to the two interplanetary shocks and attribute the European-Aragats asymmetry to a spatial anisotropy in the cosmic-ray depression. The mechanism also separates genuine FD signals from thunderstorm ground enhancements, which appear as short bursts in low-threshold detectors.

What would settle it

Searching hourly count-rate records from the worldwide neutron-monitor network for 2005-2025 and finding a Forbush decrease with a deeper minimum than the roughly 15% depletion seen at Aragats, or with two comparable minima at similar rigidity, would falsify the 'largest in 20 years' claim.

Watch

Extended reading notes

Core claim

The authors claim that a compound interplanetary coronal mass ejection, formed when the fast May 31 CME overtook the earlier May 30 CMEs, produced the largest Forbush decrease in 20 years. The first shock, detected at 05:22 UTC on June 1, initiated the first FD phase with a roughly 7.5% depletion at all SEVAN locations around 15:00 UTC on June 1. The second shock, detected at 10:19 UTC on June 2, deepened the decrease unevenly: European detectors reached 7.9% at Lomnicky Stit and 8.8% at Musala around 17:40 UTC, while Aragats showed a shallower minimum. Neutron-selected channels showed larger depletions, 12% at Mileshovka and 15% at the Aragats neutron monitor, with Nor Amberd 2% smaller due to atmospheric cutoff, and muon channels displayed a 12% depletion at a 40 MeV threshold versus 8% at 300-400 MeV thresholds. The differing amplitudes are interpreted as signatures of both global heliospheric modulation and local geomagnetic cutoff variations, with recovery taking nearly a week.

Load-bearing premise

The record claim depends on SEVAN's own measurements being sufficient to establish that no larger Forbush decrease occurred in the past 20 years, without a quantitative comparison to global neutron-monitor records.

Editorial extensions

If this is right

  • If the record claim is correct, the June 1-2, 2025 event becomes the reference Forbush decrease of solar cycle 25, against which future events will be compared.
  • Energy-differentiated muon channels would become a standard tool for separating heliospheric modulation from magnetospheric effects in real time, improving space-weather nowcasting.
  • The two-step structure and week-long recovery imply that forecasts must treat merging CMEs as compound disturbances rather than isolated shocks.
  • The observed European-Aragats anisotropy indicates that single-station measurements underestimate or miss the full depth of strong Forbush decreases, supporting the continued operation of distributed networks.
  • Intercalibration of SEVAN detectors with neutron monitors at the same sites provides a way to translate SEVAN depletion percentages into neutron-monitor-equivalent amplitudes for comparison with historical records.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A quantitative comparison with global neutron-monitor archives from 2005-2025 would either confirm the record claim or locate a comparable or deeper event, sharpening the claimed time window.
  • The European-Aragats anisotropy implies a spatial gradient in the cosmic-ray depression across roughly 2,000 km; modeling the compound ICME's magnetic structure could predict the gradient's sign and magnitude.
  • The muon spikes superimposed on the FD trend suggest that geomagnetic cutoff changes during storms contaminate low-energy muon records, so revisiting archival SEVAN data from earlier storms could reveal similar magnetospheric effects in past events.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 3 minor

Summary. The paper reports observations of a Forbush decrease (FD) on 1–2 June 2025 made with the SEVAN particle-detector network, attributing the event to two consecutive Earth-directed CMEs on 30–31 May. It describes two distinct FD minima, amplitude estimates between 7.5% and 15% depending on detector and location, a prolonged recovery, and a claimed European–Aragats anisotropy. The analysis is explicitly preliminary and is based on count-rate depletions relative to an 8-hour baseline on 31 May 2025.

Significance. If the central claim were properly supported, the event would be of substantial interest: a two-step FD with depth exceeding typical solar-cycle events, observed simultaneously by neutron and muon channels at multiple mountain altitudes, could provide valuable spectral and anisotropic information about a complex ICME event. The SEVAN network is a unique instrument with concurrent neutron, muon, and electron/gamma detection, and the paper highlights its diagnostic potential. However, the current manuscript does not yet establish the record claim, and the quantitative analysis lacks the corrections and comparisons needed for a robust scientific conclusion.

major comments (4)
  1. [Title and Abstract] The central claim is stated inconsistently and is not supported by quantitative comparison with prior events. The title and Section 2 state 'the largest Forbush decrease in 20 years' (and 'deepest Forbush Decrease in 20 years'), while the Abstract and Introduction state 'largest FD observed in solar cycle 25'. These are different claims: solar cycle 25 began in December 2019, so a 20-year record requires excluding larger events from 2005–2019 (e.g., 2005 January, 2006 December, 2015 June, 2017 September). No comparison to global neutron-monitor data or to a published FD catalog is provided anywhere in the manuscript. If a comparable or larger event occurred within the last 20 years, the headline claim fails. The authors should either supply a quantitative comparison to prior FDs (e.g., using Neutron Monitor Database data) or restrict the claim to solar cycle 25 consistently across title, abstract, and text.
  2. [Section 3, Figures 1–4] The reported depletion percentages (7.5–8.8% for upper scintillators, 12% for Mileshovka neutrons, 15% for ArNM) are given without any uncertainty estimates or corrections. In particular, no barometric pressure correction is described for the neutron monitors, which is essential for isolating the cosmic-ray modulation from atmospheric effects; the 8-hour baseline window (May 31, 08:00–16:00) is short and may include diurnal variations or transient increases, and no statistical error bars are shown in the figures. Without these, differences of ~1% between stations (e.g., 7.9% vs. 8.8%) cannot be interpreted as physically significant. Please add error bars (statistical, and where applicable systematic, from pressure/efficiency) and describe or justify the baseline normalization.
  3. [Section 3, European–Aragats anisotropy] The claimed anisotropy between European and Aragats detectors is not convincingly established. The detectors are at different altitudes (Aragats 2000/3200 m, Lomnicky Stit 2634 m, Musala 2930 m, Mileshovka 837 m) and different geomagnetic cutoffs. The observed differences in depletion depth could be largely due to atmospheric attenuation and rigidity cutoff differences, not to a spatial anisotropy of the cosmic-ray flux. The paper itself notes that NANM at 2000 m shows a 2% smaller depletion than ArNM at 3200 m, which is consistent with an altitude effect. To support the anisotropy claim, the authors should compare detectors at similar atmospheric depth or use a transport/response model to quantify the expected altitude and cutoff dependence.
  4. [Section 2, Figure 1] The association of the first FD phase with the 'cannibal' ICME and the second phase with the May 31 CME is plausible but is not quantitatively demonstrated from the in-situ data. The text lists SSC times and Btotal jumps, but does not show time profiles of the solar-wind speed, IMF Bz, or plasma density for the 31 May–3 June interval. To support the two-phase interpretation, the authors should present these interplanetary parameters alongside the cosmic-ray time series so that the shock arrivals and the ICME structures are visible rather than asserted.
minor comments (3)
  1. [Figure 1 caption] The caption is incomplete: it reads 'mean values from 8:00 to ' and then the time '16:00' appears on the next line; please fix the formatting so the full interval is stated in one place.
  2. [References and prior work] The paper cites Karapetyan et al. (2024) on a Forbush decrease observed by SEVAN in the 25th cycle, but does not compare the current event with that earlier event. A brief quantitative comparison would help support the 'largest in cycle 25' claim.
  3. [Terminology] The terms 'largest Forbush decrease' and 'deepest Forbush Decrease' are used interchangeably; consider using one consistent descriptor (e.g., 'largest amplitude' or 'deepest minimum').

Circularity Check

0 steps flagged · score 1.0 of 10

No significant circularity: the FD amplitudes are direct detector count-rate depletions against an explicit pre-event baseline, and the record claim, though under-supported, is not derived from itself.

full rationale

The paper is an observational report. The measured FD depths are computed as count-rate depletions relative to a stated pre-event interval: 'The depletion percentage was calculated relative to the mean values from 8:00 to 16:00 on May 31.' This is a measurement convention, not a fitted parameter, and it does not encode the headline claim. The 'largest FD in 20 years' assertion is an empirical comparison claim, but no circular reduction is exhibited: the paper does not define 'largest' in terms of its own baseline, nor does it fit a parameter and then repredict the same quantity. The many self-citations establish detector design, calibration, and prior SEVAN operations; they are not load-bearing for the FD amplitudes or the 'largest' claim. The title/abstract inconsistency ('20 years' vs 'solar cycle 25') and the absence of a quantitative comparison to global neutron-monitor FD catalogs are support and correctness concerns, not circularity. No equation or derivation in the paper reduces to its own input. Therefore the circularity score is low.

Assumptions & free parameters 1 free parameters · 3 assumptions · 0 invented entities

No fitted parameters or invented entities are introduced. The main ledger items are the chosen baseline and standard domain assumptions about detector response and shock timing. The absence of a comparative dataset for the 'largest in 20 years' claim is the key unsupported element.

free parameters (1)
  • Baseline interval for depletion normalization = May 31 08:00-16:00 UTC
    The percentage depletions in Figures 1-3 are computed relative to this 8-hour window. Choosing a different quiet-time reference would change all quoted amplitudes and potentially the reported event depth.
assumptions (3)
  • domain assumption The May 31 08:00-16:00 UTC count-rate average represents the quiet pre-event cosmic ray level
    The entire depletion scale depends on this baseline being representative of the undisturbed flux; there is no check for pre-event variations or diurnal effects.
  • domain assumption Neutron detectors respond to ~1-20 GeV primary cosmic rays while muon detectors sample 10-1000 GeV primaries
    Invoked in Section 4 to interpret the different amplitudes as energy-dependent modulation; treated as established, not validated here.
  • domain assumption The SSC signatures at L1 at 05:22 UTC June 1 and 10:19 UTC June 2 correspond to the arrival of the interplanetary shocks at Earth and to the onset of the FD phases
    Used in Section 2 to time the FD phases; assumes L1-to-Earth propagation delay is negligible or already accounted for, which is not stated.

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Cite this review

Pith. "Pith review of The largest Forbush decrease in 20 years: Preliminary analysis of SEVAN network observations." pith.science (2026). https://pith.science/paper/YIJBISSQ

@misc{pith2026250617917,
  author       = {Pith},
  title        = {Pith review of: The largest Forbush decrease in 20 years: Preliminary analysis of SEVAN network observations},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/YIJBISSQ}},
  note         = {Machine review of arXiv:2506.17917}
}
read the original abstract

We present a preliminary analysis of the largest Forbush Decrease (FD) observed in solar cycle 25 using SEVAN network data. Triggered by consecutive Earth-directed CMEs on May 30 and 31, 2025, this event produced two distinct FD minima and a prolonged recovery, with significant anisotropies in cosmic ray response across the network. The timing of interplanetary shock arrivals was confirmed by SSC signatures at 05:22 UTC on June 1 and 10:19 UTC on June 2, marking the onset of each FD phase. The depth and temporal structure of the FD varied across SEVAN detectors, providing insights into the complex heliospheric and magnetospheric dynamics during this multi-CME event.

Discussion (0). Continue with ORCID to comment.

Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Rigidity spectra and onset geometry of the two largest Forbush decreases of solar cycle 25 from visibility-graph curvature

    astro-ph.IM 2026-07 conditional novelty 4.0 of 10

    Visibility-graph Forman-Ricci curvature collapses at the onset of the two largest solar-cycle-25 Forbush decreases and tracks their rigidity spectra.

Reference graph

Works this paper leans on

16 extracted references · 15 canonical work pages · cited by 1 Pith paper

  1. [1]

    The largest Forbush decrease in 20 years: Preliminary analysis of SEVAN network observations. A. Chilingarian, T.Karapetyan, B.Sargsyan Yerevan Physics Institute Alikhanyan Brothers 2, Yerevan 36, Armenia Abstract We present a preliminary analysis of the largest Forbush Decrease (FD) observed in solar cycle 25 using SEVAN network data. Triggered by consec...

    work page 2025

  2. [2]

    Introduction The SEVAN network (Space Environment Viewing and Analysis Network), as part of the United Nations Basic Space Science (UNBSS) activities, was supported by the International Heliophysical Year 2007 (IHY 2007, Thompson et al.,

    work page 2007

  3. [3]

    cannibal

    SEVAN network response to geomagnetic disturbances Significant disturbances in the magnetosphere caused large variations in cosmic ray flux, as measured on Earth’s surface by neutron monitors and SEVAN detectors. The two-phase Forbush decrease began on June 1 and was extended by successive ICMEs, prolonging the recovery period for a week. Figure 1 display...

    work page 2000

  4. [5]

    Solar and Interplanetary sources On May 29, 2025, a G3-level geomagnetic storm began, driven by a coronal hole high-speed stream (CH HSS) that rotated into a geoeffective position, sending fast solar wind toward Earth. As the stream moved forward, it interacted with a co-rotating interaction region (CIR), a compression zone between slow and fast solar win...

    work page 2025

  5. [7]

    Forbush decrease observed by ArNM (3200 m) and NANM (2000 m). Muon detectors with different energy thresholds are very useful for classifying solar events and assessing the primary solar proton energy at ground-level enhancements (GLEs) and magnetospheric effects (MEs) (Chilingarian et al., 2024b; 2024c). Figure 4 shows how the STAND3 detector’s coinciden...

    work page 2000

  6. [9]

    Aragats Space- Environmental Center: Status and SEP forecasting possibilities. J. Phys. G Nucl. Part Phys. 29, 939–952. https://doi.org/10.1088/0954-3899/29/5/314. Chilingarian, A., Avakyan, K., Arakelyan, K., et al., 2009d. Space Environmental Viewing and Analysis Network (SEVAN). Earth Moon Planets 104, 195–210. https://doi.org/10.1007/s11038-008-9288-1...

    work page doi:10.1088/0954-3899/29/5/314

  7. [28]

    doi.org/10.1186/s40623-020-01155-9 Forbush, S.E.,

    work page doi:10.1186/s40623-020-01155-9

  8. [146]

    doi: 10.1209/0295-5075/ad329c Chilingarian A., Karapetyan T., Sargsyan B., Asatryan K., Gabaryan G

    24001. doi: 10.1209/0295-5075/ad329c Chilingarian A., Karapetyan T., Sargsyan B., Asatryan K., Gabaryan G. (2024c) Influence of Interplanetary Coronal Mass Ejections on Terrestrial Particle Fluxes Through Magnetosphere Disturbances, EPL 148, 19001. doi:10.1209/0295 5075/ad7e4c Chilingarian, A., Aslanyan, D., Sargsyan, B., and Kozliner, L. 2025, Wind-induc...

    work page doi:10.1209/0295-5075/ad329c 2024

Show all 16 references
  1. [525]

    Karapetyan T., Chilingarian A., Hovsepyan G., et al. 2024, The Forbush decrease observed by the SEVAN particle detector network in the 25th solar activity cycle, Journal of Atmospheric and Solar-Terrestrial Physics 262, 106305 Thompson, B.J., Gopalswamy, N., Davila, J.M., Haub...

    2024

  2. [1954]

    World-wide cosmic-ray variations in 1937-1952. J. Geophys. Res. 59,

    1937

  3. [2003]

    The network's initial rollout included installations in Croatia, Bulgaria, and India (Chilingarian et al., 2009)

    at the Yerevan Physics Institute developed a new hybrid particle detector that measures neutral and charged particles. The network's initial rollout included installations in Croatia, Bulgaria, and India (Chilingarian et al., 2009). Expansion continued with the installation of...

    2009

  4. [2010]

    82, 043009

    Ground-based observations of thunderstorm-correlated fluxes of high-energy electrons, gamma rays, and neutrons, Phys Rev D. 82, 043009. doi.org/10.1103/PhysRevD.82.043009 Chilingarian A, Hovsepyan G., and Hovhannisyan A

    doi

  5. [2011]

    Particle bursts from thunderclouds: Natural particle accelerators above our heads, Phys. Rev.. D 83, 062001. doi.org/10.1103/PhysRevD.83.062001 Chilingarian A., Babayan V., Karapetyan T., et al. (2018) The SEVAN Worldwide network of particle detectors: 10 years of operation, A...

    2018 doi

  6. [2020]

    The latest discovery was a significant increase in gamma radiation during winter snowstorms (Chilingarian et al., 2025)

    and estimating maximum values of atmospheric electric fields (Chilingarian et al., 2021). The latest discovery was a significant increase in gamma radiation during winter snowstorms (Chilingarian et al., 2025). With the maximum of the 25th solar activity cycle reached, SEVAN p...

    2021

  7. [2023]

    Most influenced by geomagnetic disturbances are 40 MeV muons, showing 12% depletion

    pictured the FD, which separates muons with different threshold energies. Most influenced by geomagnetic disturbances are 40 MeV muons, showing 12% depletion. Another muon detector at Aragats, with energy thresholds of 300 and 400 MeV, shows only an 8% depletion. In Figure 4, ...

    2010

  8. [2680]

    Hovsepyan (2023) Proving ‘‘new physics’’ by measuring cosmic ray fluxes, Astronomy and Computing 44, 100714

    Chilingarian A., G. Hovsepyan (2023) Proving ‘‘new physics’’ by measuring cosmic ray fluxes, Astronomy and Computing 44, 100714. https://doi.org/10.1016/j.ascom.2023.100714 Chilingarian A. (2024) The Solar Modulation Events of the 25th Solar Activity Cycle as Seen by Particle ...

    2023

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Reviewed August 6, 2026 · model on record in the stance chip above.