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REVIEW 4 major objections 6 minor 2 references

Statistical analysis of interplanetary shock waves measured by a Solar Wind Analyzer and a magnetometer onboard the Solar Orbiter Mission in 2023

T0 review · 4 major / 6 minor · reviewed 2026-08-06 · deepseek-v4-flash

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Pith's one-line read This paper claims that a semi-automated algorithm built on simultaneous jumps in density, speed, and magnetic field detects 44 interplanetary shocks in Solar Orbiter data during 2023, and that the rate of shocks per observing time rises…

desk verdict A potentially useful 2023 SolO shock catalog is undercut by a Mach-number formula that omits the shock speed, producing three sub-magnetosonic 'shocks' in the table. read the letter →

arxiv 2506.19986 v1 pith:MQRWAYHT submitted 2025-06-24 astro-ph.SR physics.space-ph

Oleksandr Yakovlev , Oleksiy Dudnik , Anna Wawrzaszek This is my paper · ORCID
classification astro-ph.SRphysics.space-ph
keywords interplanetaryshockssolarwindOrbitershockdetectionalgorithmMachnumberplasmabetaheliocentricdistancecycle25
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

This paper adapts a previously published automated shock-detection algorithm to data from Solar Orbiter's proton sensor and magnetometer and applies it to the whole year 2023, when the spacecraft was between 0.29 and 0.95 AU from the Sun. The authors report 44 interplanetary shocks—40 fast forward, 2 fast reverse, 1 slow forward, and 1 slow reverse—and tabulate their compression ratios, Mach numbers, upstream plasma beta, and the angle between the shock normal and magnetic field. Most shocks are quasiperpendicular, with the angle peaked near 50 degrees, and most have upstream beta below 1, indicating magnetic-field-dominated dynamics. After normalizing by the time the spacecraft spent in each radial distance segment, the number of shocks per unit time increases toward larger heliocentric distances. The result is a year-long, instrument-specific shock catalog from the ascending phase of solar cycle 25, providing a basis for space-weather and shock-acceleration studies.

What carries the argument

The detection machinery is a set of relative step-change thresholds applied to a 300-second sliding window: density change ΔN > 0.35, speed change ΔV > 0.05, and magnetic-field magnitude change ΔB > 0.30, combined with two quality factors QF1 = (ΔB + ΔN + ΔV)/3 and QF2 = ΔB/4 + ΔN/12 + 2ΔV/3 exceeding 0.25 and 0.15, plus auxiliary conditions that the changes occur simultaneously and that the downstream speed is lower than the upstream speed. Shock parameters are then derived from 5-minute upstream and downstream averages using standard single-spacecraft techniques, including magnetic-field and density compression ratios, upstream plasma beta, Alfvén Mach number, and the shock-normal angle via a magnetic coplanarity method.

What would settle it

Compare the 44 claimed events one by one against the raw Solar Orbiter L2 data and against independent shock identifications for the same spacecraft and dates; if many claimed shocks lack simultaneous jumps in density, speed, and magnetic field above the stated thresholds, or if events listed in independent catalogs are systematically missing, the central claim is undermined.

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Extended reading notes

Core claim

Using simultaneous step changes in proton density, speed, and magnetic-field magnitude, combined with two quality factors, the authors claim to have detected 44 interplanetary shocks in Solar Orbiter data during 2023. The catalog's composition is strongly dominated by fast forward shocks (40 of 44). The statistical distributions show that the angle between the shock normal and the upstream magnetic field clusters around 50 degrees, so most events are quasiperpendicular, and upstream plasma beta is below unity for the majority of events. After dividing the heliocentric distance range into ten equal segments and normalizing the shock count by the time spent in each segment, the normalized shock frequency increases with distance from the Sun. The authors also report that compression ratios and quality factors peak around 0.63 AU, tied to one strong event rather than a statistically averaged trend.

Load-bearing premise

The detection thresholds were picked by inspecting histograms of the same set of roughly 50 candidate events that later produced the 44-shock list, so the catalog membership and the reported distance trend rest on thresholds that were not checked against an independent, labeled sample.

Editorial extensions

If this is right

  • The 44-event list provides a reference set of interplanetary shocks in the ascending phase of solar cycle 25 at heliocentric distances of 0.29 to 0.95 AU.
  • The strong dominance of fast forward shocks and quasiperpendicular geometries can be compared with shock populations observed at other phases of the solar cycle and by other missions.
  • The increasing normalized shock rate with distance supports the picture that the observed shock count grows as the spacecraft's whole-sky spatial coverage in the Sunward direction expands and as CME-driven shocks develop further from the Sun.
  • The stated thresholds and algorithm can be applied to Solar Orbiter data from later years to track how shock properties evolve through solar cycle 25.
  • The finding that most events have upstream plasma beta below 1 indicates that magnetic pressure dominates thermal pressure at these shock fronts, which matters for particle-acceleration models.
  • The comparison with publicly documented shock counts for the same year gives a quick consistency check, though the aggregate numbers differ by up to nine events.

Reading between the lines

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

  • Event-by-event agreement with the independent catalogs the paper cites would test whether the algorithm's extra sensitivity is real or an artifact of threshold choices; the paper only compares aggregate counts, not individual events.
  • Because the thresholds were chosen from the same candidate set that produced the final list, the reported increase of shock rate with distance could partly reflect selection effects; applying the algorithm to 2024 data would show whether the thresholds transfer to an independent period.
  • The few events with extreme parameters, such as the one with Alfvén Mach number near 25, may be attractive targets for dedicated studies of particle acceleration, similar to other high-Mach-number shocks discussed in the literature.
  • Connecting each shock time to the flare and coronal mass ejection lists the paper begins to use could test whether the local peak in shock parameters around 0.63 AU is associated with a specific solar eruption, a hypothesis the authors raise but do not fully verify.
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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 / 6 minor

Summary. The paper presents a semi-automated shock detection algorithm adapted from Kruparova et al. (2013) and applies it to Solar Orbiter SWA-PAS and MAG data for the full year 2023, identifying 44 interplanetary shocks (40 fast-forward, 2 fast-reverse, 1 slow-forward, 1 slow-reverse) at heliocentric distances of 0.29–0.95 AU. For each event, the paper reports compression ratios, quality factors, upstream plasma beta, shock-normal angle, Alfvén speed, sound speed, fast-magnetosonic speed, and Mach numbers. It also presents distributions of theta_Bn and beta_us, and a heliocentric-distance-normalized shock rate that is claimed to increase with radial distance.

Significance. If the catalog and its parameters are reliable, the paper would provide a useful addition to interplanetary-shock statistics in the ascending phase of solar cycle 25, exploiting Solar Orbiter's unique inner-heliospheric coverage. Strengths include the use of high-resolution SWA-PAS and MAG data, the public presentation of a 44-event list with parameters, and the comparison of aggregate event counts with the ipshocks and Serpentine databases. However, the central claim is not currently supported because the detection thresholds are chosen in-sample from the same candidates that form the final list, and Table 2 contains events with fast-magnetosonic Mach numbers below 1, which is physically impossible for a shock. These issues bear directly on catalog membership, all derived parameter statistics, and the reported radial trend, so they must be resolved before the results can be accepted.

major comments (4)
  1. [Section 3.1, Figures 1–2] The detection thresholds (delta_N > 0.35, delta_V > 0.05, delta_B > 0.30, QF1 > 0.25, QF2 > 0.15) are obtained by inspecting histograms of the same ~50 candidates that are subsequently filtered into the final 44-event list. This is an in-sample threshold choice with no independent validation set. The comparison with ipshocks and Serpentine totals (35 and 43 events) is aggregate only, not event-by-event, so it does not establish that the 44 events are true shocks or that the type mix is correct. The catalog membership and all derived distributions are therefore partly a restatement of the threshold choices. Please provide an out-of-sample validation (e.g., event-by-event comparison with the Serpentine or ipshocks lists) or a sensitivity analysis showing the catalog is stable under reasonable threshold variations.
  2. [Section 3.2, Eq. (15) and Table 2] Equation (15) defines Mfms = |V_us·n| / V_fms, omitting the shock speed V_sh computed in Eq. (11). The fast-magnetosonic Mach number must be evaluated in the shock frame, i.e., |V_sh − V_us·n| / V_fms (with an appropriate sign convention). As written, Eq. (15) yields Mfms < 1 for events #5 (0.72), #11 (0.41), and #22 (0.76), which is physically impossible for a fast shock and contradicts the paper's own identification of these events as FF/SR shocks. Either the formula is wrong, in which case all Mach numbers in Table 2 and all statistics based on them are unreliable, or these events are not shocks, in which case the catalog contains false positives. Please correct Eq. (15) (and the ambiguous ± sign in Eq. (14)) and recompute the Mach numbers, then re-examine whether the remaining events satisfy Mfms > 1 and MA > 1.
  3. [Section 3.2, Tables 1–2] No uncertainties are given for theta_Bn, V_sh, MA, or Mfms. The MX3 single-spacecraft normal method is sensitive to the choice of upstream/downstream averaging windows and to noise, and the paper itself notes that the 5-minute window was chosen after trying 5–10 minute intervals. Because the paper's statistical conclusions (e.g., the peak at theta_Bn ~ 50° in Fig. 5a and the claim that most shocks are quasi-perpendicular) depend on these point estimates, please provide error bars or a sensitivity analysis over averaging windows and normal-method variants.
  4. [Section 3.4, Figure 7] The claim that the distance-normalized shock rate N_IP_Rd increases with Rd is based on 44 events divided into 10 bins, and the authors note that one strong event at ~0.63 AU dominates the parameter maxima. The paper does not test whether the radial trend is robust to the threshold choices or to removal of outlier events, nor does it account for the small number of events per bin after normalization. Please provide Poisson error bars and a robustness check of the trend, for example by recomputing the rate with alternative thresholds or by excluding the dominant event.
minor comments (6)
  1. [Eq. (16)] The expression for V_fms is dimensionally incorrect as written (the factor 1/2 is placed outside instead of taking the square root of the whole expression). The numerical values in Table 2 suggest the intended formula was used, so please fix this typographical error.
  2. [Eq. (14)] The ± sign before V_sh in Eq. (14) is ambiguous; please specify the sign convention for forward and reverse shocks and how it relates to V_sh from Eq. (11).
  3. [Section 3.3, Fig. 5a] The histogram in Fig. 5a is described as showing the largest counts at theta_Bn ~ 50°, but the bin width and the sample size per bin are not stated; please provide these details for clarity.
  4. [Abstract and Section 3.2] The abstract says 'over 40 IP-shock waves' while the text specifies 44; please use consistent numbers throughout.
  5. [Table 1 and Annex C] The column 'Angle S–E' is only defined in Annex C, not in the main text; this makes Table 1 difficult to interpret without jumping to the annex.
  6. [Section 3.2 and References] The comparison with the ipshocks and Serpentine databases should state the version or access date of the catalogs used, because these lists are updated over time.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the shock catalog and derived parameters follow from the stated algorithm and data, with only a methodological threshold-tuning concern that is not a circular reduction.

full rationale

The paper's derivation chain is not circular. The final catalog of 44 shocks is produced by applying explicit thresholds and quality factors to Solar Orbiter SWA-PAS and MAG data, and the shock parameters are computed from stated formulas (Eqs. 6-16). The threshold values in Section 3.1 are chosen by inspecting histograms of the same ~50 candidate events, which is a legitimate methodological limitation and a potential source of selection bias or overfitting, but it is not a circular reduction: the paper does not fit a parameter to a target result and then rename that fit as a prediction. The 44-event list is a filter output, not a fitted quantity, and the paper presents external comparisons with ipshocks and Serpentine catalogs as independent, though incomplete, benchmarks. There is no load-bearing self-citation: the detection method is attributed to Kruparova (2013), and the authors do not cite their own prior work as the basis for the central claim. The concern about Eq. (15) omitting V_sh and yielding sub-magnetosonic Mach numbers in Table 2 is a physical/correctness issue, not circularity. Overall, the central claim is self-contained against the data and stated equations, so no circular step is identified.

Assumptions & free parameters 5 free parameters · 5 assumptions · 0 invented entities

No new physical entities are introduced. The catalog and trends rest on threshold choices from the same dataset and standard single-spacecraft shock analysis assumptions, which are reasonable but not independently verified.

free parameters (5)
  • Primary detection thresholds for delta_N, delta_V, delta_B = 0.35, 0.05, 0.30
    Set to where the 2023 candidate histograms group (Section 3.1); these thresholds determine which of the ~50 candidates become the final 44 shocks.
  • QF1 and QF2 thresholds = 0.25, 0.15
    Chosen from count distributions in Figure 2; a candidate passes if QF1 > 0.25 or QF2 > 0.15.
  • Averaging window delta_t = 300 s
    Fixed 5-minute window for relative changes and upstream/downstream averages (Sections 2.2 and 3.2); affects all parameter estimates.
  • Secondary exclusion thresholds = delta_B > 0.1, delta_N > 0.1, delta_V > 0.03, V1 > V2
    Additional criteria listed in Section 3.1 that remove weak or negative-velocity-step events and shape the final list.
  • Electron temperature radial fit coefficients = 146277 K at 1 AU, exponent -0.664
    Used in Eq. 13 to compute Te, Cs, and Mfms; taken from Chart 2011, not validated for the 2023 SolO data.
assumptions (5)
  • domain assumption Five-minute averaged SWA-PAS and MAG L2 data are sufficient to resolve shock transitions
    Section 2.2 applies relative-change calculations over delta_t = 300 s; unresolved sub-window structure and interpolation between 4-s plasma and 0.125-s magnetometer data may alias true jumps.
  • domain assumption Single-spacecraft MX3 method gives reliable shock normals
    Section 3.2 uses MX3 (Abraham-Shrauner 1976, Schwartz 1998) on one spacecraft; no multi-spacecraft or timing validation and no error propagation.
  • domain assumption Proton moments represent total solar wind density and pressure
    Beta and Alfven speed (Eqs. 8-9) use proton density and temperature; alpha particles and electron pressure are not included.
  • domain assumption Adiabatic index gamma = 5/3 and isotropic plasma apply to these shocks
    Used in Eq. 12 for sound speed; collisionless shock microphysics can violate isotropy and closure assumptions.
  • domain assumption The radial electron temperature profile from Chart 2011 applies to all SolO 2023 distances
    Equation 13 is a Ulysses-based empirical relation; its use affects Cs and Mfms for all 44 events.

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Cite this review

Pith. "Pith review of Statistical analysis of interplanetary shock waves measured by a Solar Wind Analyzer and a magnetometer onboard the Solar Orbiter Mission in 2023." pith.science (2026). https://pith.science/paper/MQRWAYHT

@misc{pith2026250619986,
  author       = {Pith},
  title        = {Pith review of: Statistical analysis of interplanetary shock waves measured by a Solar Wind Analyzer and a magnetometer onboard the Solar Orbiter Mission in 2023},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/MQRWAYHT}},
  note         = {Machine review of arXiv:2506.19986}
}
abstract

Interplanetary (IP) shock waves are greatly interesting, as they represent significant phenomena in near-Earth space and are direct drivers of geomagnetic and radiation storms. Moreover, various data and parameters are being explored for the identification and characterization of these waves. The spatial dimensions of shock waves vary significantly with the conditions and parameters of the propagating medium. For example, the radii of curvature of the shock wave fronts can vary by several hundred Earth radii or more in the inner heliosphere. In this study, we improved the semi-automated identification of shock waves by analyzing the solar wind and IP magnetic field (MF) parameters. More precisely, we analyzed the data recorded by the Proton Alpha Sensor of the Solar Wind Analyzer (SWA-PAS) and magnetometer (MAG) onboard the Solar Orbiter (SolO) mission. These data were collected and analyzed during the SolO journey around the Sun in 2023 at distances of 0.29...0.95 AU. Employing the developed algorithm, we identified over 40 IP-shock waves that occurred in 2023 using SWA-PAS and MAG. Additionally, we determined and presented a list of shock types and their basic parameters, kinetic and magnetohydrodynamic. The compression ratios, plasma beta ${\beta}_{us}$, angle between the shock normal and upstream MF ${\theta}{_B}{_n}$, Mach number, and others were among these parameters. Furthermore, we investigated the statistical distributions of the ${\theta}{_B}{_n}$ and ${\beta}_{us}$ parameters in the upstream region. Finally, the dependence of number of the identified shock waves as a function of the distance away from the Sun was explored; the number of shocks increased gradually with the increasing heliocentric distance.

Figures

Figures reproduced from arXiv: 2506.19986 by the authors.

Figure 1
Figure 1. Dependence of the shock wave candidate counts (left vertical axis in all the panels) on the relative changes in the SW N, ΔN (a); V, ΔV (b); and IMF, ΔВ (c). The red vertical lines represent the selected thresholds for identifying the shock waves: 0.35, 0.05, and 0.30 for ΔN, ΔV, and ΔB, respectively [PITH_FULL_IMAGE:figures/full_fig_p005_1.png] view at source ↗
Figure 2
Figure 2. Dependence of the shock wave candidate counts (left vertical axis in all the panels) on QF1 (a) and QF2 (b). The red vertical lines represent the selected thresholds for identifying the shock waves. The additional conditions for including the candidates in the list of shock waves are indicated below: • event quality factor Q > QF1 or Q > QF2 (basic selection condition); • simultaneous level excesses: ΔB > 0.1, ΔN > … view at source ↗
Figure 3
Figure 3. Dynamics of the SW and IMF parameters: N (a), V (b), Btot (c), ΔN (d), ΔV (e), and ΔB (f). Panels (g) and (h) display the changes in QF1 and QF2. The numerical values of the parameter thresholds are displayed in the right panels and marked by red horizontal lines. 3.2. Basic parameters of the shock waves. Here, 44 IP shocks (40 FF, 2 FR, 1 SF, and 1 SR) were identified using the algorithm described in Sections 2 and… view at source ↗
Figures from the paper (4 more)
Figure 4
Figure 4. Figure 4: Dependences of rB (a), rN (b), QF1 (c), and QF2 (d) as functions of the distance between the SolO and Sun for each shock wave presented in [PITH_FULL_IMAGE:figures/full_fig_p009_4.png]
Figure 5
Figure 5. Figure 5: а shows the largest counts of the undoubtedly shock waves were recorded at the SolO location, and it was quasiperpendicular, with an angle (𝜃𝜃Bn) of ~50° [PITH_FULL_IMAGE:figures/full_fig_p010_5.png]
Figure 6
Figure 6. Figure 6: Distributions of the shock waves recorded by the SWA-PAS and MAG instruments in 2023 along the SolO trajectory compared with the X-, M-, and C-class solar flares obtained from the STIX Data Center. The dark dots in panels a and b indicate the daily average (UTC ≈ 12:00…
Figure 7
Figure 7. Figure 7: а) Dependence of the number of shock waves (IPn) as a function of Rd; b) Dependence of the time spent on passing a particular segment (length = 0.067 AU; Ts) as a function of Rd; NIP_Rd is the ratio of IPn on each segment (IPs) to Ts as a function of Rd. The dependence…

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Works this paper leans on

2 extracted references · 2 canonical work pages

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    https://doi.org/10.1007/s11207-012-9967-y. Dimmock, AP, Gedalin, M, Lalti, A, Trotta, D, Khotyaintsev, YV, Graham, DB, Johlander, A, Vainio, R, Blanco- Cano, X, Kajdiˇ, P, Owen, CJ, Wimmer -Schweingruber, RF. 2023. Backstreaming ions at a high Mach number interplanetary shock. Astron. Astrophys., 679: A106. https://doi.org/10.1051/0004-6361/202347006. Ech...

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