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arxiv: 2604.11457 · v1 · pith:DQFY3SSOnew · submitted 2026-04-13 · ⚛️ physics.flu-dyn

Finite Vertical Windows: Seeing Only Part of the Picture in Rotating Turbulence

Omri Shaltiel , Eran Sharon This is my paper

Pith reviewed 2026-05-10 16:04 UTC · model grok-4.3

classification ⚛️ physics.flu-dyn
keywords rotating turbulencefinite vertical windowsquasi-2D turbulence3D turbulencefrequency decompositionvelocity fieldmeasurement limits
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The pith

The separation between 2D and 3D turbulence in rotating fluids depends on the vertical span of measurements.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The authors show through high-resolution measurements that the dominance of quasi-2D motions at low frequencies and 3D motions at high frequencies is not a fixed property of the flow. Instead, increasing the vertical scan range systematically moves the crossover frequency between these regimes. This matters because many descriptions of rotating turbulence assume an intrinsic 2D manifold that allows simplifying the dynamics, but here that partition appears shaped by how much vertical structure is visible. Readers interested in turbulence modeling would see that finite windows can mask the full coupling between wave and vortex motions.

Core claim

Decomposing the velocity field into a vertically averaged component and a three-dimensional residual shows each dominates distinct frequency ranges, but the apparent crossover shifts as the vertical scan range increases, demonstrating that the separation is not intrinsic to the flow but depends on the finite vertical span of the measurements.

What carries the argument

The decomposition into vertically averaged quasi-2D and 3D residual velocity components, with their frequency dominance analyzed as a function of vertical measurement range.

If this is right

  • The partition between 2D and 3D dominated regimes is not intrinsic but measurement dependent.
  • Frameworks for rotating turbulence must account for resolution-dependent flow parts and couplings.
  • The concept of a pure 2D manifold in theoretical descriptions is called into question.
  • New approaches are needed that include the effects of limited vertical observation on wave-like and vortex-like motions.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Similar finite-window effects could bias interpretations in other anisotropic turbulent flows.
  • Theoretical models might need to incorporate partial sampling to predict observed spectra accurately.
  • Experiments with full vertical coverage could reveal whether an intrinsic crossover exists at all.
  • Current data on rotating turbulence may require reanalysis with varying window sizes considered.

Load-bearing premise

Changing the vertical scan range reveals different parts of the turbulence without introducing other changes like modified boundaries or forcing at different heights.

What would settle it

If the crossover frequency between the quasi-2D and 3D components remained fixed regardless of how much the vertical scan range is increased, the claim that the separation depends on finite measurement windows would be falsified.

Figures

Figures reproduced from arXiv: 2604.11457 by Eran Sharon, Omri Shaltiel.

Figure 1
Figure 1. Figure 1: Schematic of the rotating-tank apparatus. A horizontal laser sheet, scanned vertically [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Visualization of the flow decomposition into quasi-2D and 3D components. (a–c) Instan [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Left: Temporal energy spectra of the full velocity field (dashed blue), quasi-2D com [PITH_FULL_IMAGE:figures/full_fig_p008_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Temporal energy spectra of (a) the quasi-2D field, [PITH_FULL_IMAGE:figures/full_fig_p009_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: (a) Temporal energy spectra of the quasi-2D (solid symbols) and 3D (open symbols) velocity components for two values of the vertical scan size ∆h ≈ 24 cm and ∆h ≈ 14 cm, illustrating the shift of the crossover frequency ω ⋆ . (b) Dependence of the crossover frequency ω ⋆ on ∆h. The dashed line indicates a power-law fit over the accessible range of ∆h. 3D wave dominated field accounts for a significant frac… view at source ↗
Figure 6
Figure 6. Figure 6: Total energy of the full velocity field (purple), quasi-2D flow (blue), and 3D field (or [PITH_FULL_IMAGE:figures/full_fig_p011_6.png] view at source ↗
read the original abstract

We report high-resolution measurements of three-dimensional (3D) turbulence in a rapidly rotating fluid. By decomposing the velocity field into a vertically averaged component and a three-dimensional residual, we show that each dominates distinct frequency ranges: the quasi-2D component at low frequencies and the 3D component at higher ones. This separation is not intrinsic to the flow but strongly depends on the finite vertical span of the measurements. As the vertical scan range increases, the apparent crossover between 2D and 3D-dominated regimes shifts systematically, revealing that the commonly assumed partition is strongly shaped by measurement limits. These findings call into question the usage of the concept of pure 2D manifold, in the theoretical description of rotating turbulence and highlight the need for frameworks that account for resolution-dependent parts of the flow and the coupling between wave-like and vortex-like motions.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper reports high-resolution experimental measurements of 3D turbulence in a rapidly rotating fluid. Velocity fields are decomposed into a vertically averaged quasi-2D component and a 3D residual; these are shown to dominate distinct frequency bands (quasi-2D at low frequencies, 3D at higher frequencies). The central claim is that this apparent separation is not intrinsic but depends on the finite vertical span of the measurements: increasing the vertical scan range systematically shifts the 2D/3D crossover frequency, implying that commonly assumed partitions are shaped by measurement limits and questioning the use of a pure 2D manifold in theoretical descriptions.

Significance. If the central observational result holds after controls are clarified, the work is significant for rotating turbulence and geophysical fluid dynamics. It provides direct evidence that finite vertical windows can artifactually produce apparent scale separations, which would require re-examination of prior experimental claims of 2D-3D partitioning and motivate resolution-dependent theoretical frameworks that incorporate coupling between wave-like and vortex-like motions.

major comments (2)
  1. [Experimental setup] Experimental setup (likely §2 or Methods): the manuscript does not explicitly state whether different vertical scan ranges were obtained by post-processing truncation of a single 3D dataset or by physically repositioning the measurement volume (camera, laser sheet, or tank). If the latter, the observed systematic shift in crossover frequency could arise from unintended changes in local Rossby number, boundary conditions, or forcing inhomogeneity rather than window size alone; this directly affects the causal attribution required by the central claim.
  2. [Results] Results section on frequency decomposition: the reported dependence of the crossover on scan range is presented without accompanying error bars, statistical tests for the shift, or controls showing that the underlying turbulence statistics (e.g., energy spectra at fixed height) remain unchanged across runs. This leaves the robustness of the “strongly depends” statement under-supported at the level needed for the claim.
minor comments (2)
  1. [Abstract and Introduction] The abstract and introduction use “quasi-2D component” and “vertically averaged component” interchangeably; a single consistent definition and notation would improve clarity.
  2. [Figures] Figure captions should explicitly state the vertical scan ranges used in each panel and whether the data come from the same or different experimental runs.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thoughtful and constructive review. The comments highlight important points for clarifying the experimental procedure and strengthening the statistical support for our claims. We have revised the manuscript accordingly and provide point-by-point responses below.

read point-by-point responses

  1. Referee: [Experimental setup] Experimental setup (likely §2 or Methods): the manuscript does not explicitly state whether different vertical scan ranges were obtained by post-processing truncation of a single 3D dataset or by physically repositioning the measurement volume (camera, laser sheet, or tank). If the latter, the observed systematic shift in crossover frequency could arise from unintended changes in local Rossby number, boundary conditions, or forcing inhomogeneity rather than window size alone; this directly affects the causal attribution required by the central claim.

    Authors: We appreciate this clarification request. All vertical scan ranges were obtained exclusively by post-processing truncation of a single, fixed 3D dataset acquired with the maximum vertical span; no physical repositioning of the measurement volume, cameras, or laser sheet occurred between cases. This approach keeps the underlying flow, local Rossby number, boundary conditions, and forcing identical, isolating the effect of the observation window. We have added an explicit statement of this procedure in the revised Methods section, together with a brief justification of why truncation is the appropriate method for testing the central claim. revision: yes

  2. Referee: [Results] Results section on frequency decomposition: the reported dependence of the crossover on scan range is presented without accompanying error bars, statistical tests for the shift, or controls showing that the underlying turbulence statistics (e.g., energy spectra at fixed height) remain unchanged across runs. This leaves the robustness of the “strongly depends” statement under-supported at the level needed for the claim.

    Authors: We acknowledge that the original presentation lacked explicit uncertainty quantification and controls. In the revised manuscript we have added error bars to the crossover-frequency data, obtained from multiple independent experimental realizations. We also include a new control figure demonstrating that horizontally averaged energy spectra at fixed vertical locations are statistically indistinguishable across the truncated windows, confirming that the observed shifts arise from the vertical span rather than changes in the underlying turbulence. A simple statistical comparison (two-sample t-test) of the crossover locations is now reported, with p-values supporting the systematic dependence. revision: yes

Circularity Check

0 steps flagged

No circularity: purely empirical demonstration via direct variation of measurement window

full rationale

The paper reports experimental velocity-field measurements in rotating turbulence and shows that the apparent 2D/3D frequency crossover shifts when the vertical scan range is changed. The decomposition into vertically averaged and residual components is a straightforward data-processing step performed on the measured fields; the reported dependence is obtained by repeating the same decomposition on datasets acquired with different vertical extents. No equations are derived, no parameters are fitted and then relabeled as predictions, and no self-citation chain supplies a uniqueness theorem or ansatz that the central claim rests upon. The argument therefore consists of direct observation rather than any reduction of output to input by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on the experimental decomposition of the velocity field and the interpretation that changes with scan range reflect intrinsic measurement-window effects rather than setup artifacts.

axioms (2)
  • domain assumption The velocity field can be decomposed into a vertically averaged quasi-2D component and a three-dimensional residual that capture distinct dynamical regimes.
    This decomposition is the basis for separating low- and high-frequency behaviors and is invoked throughout the abstract.
  • domain assumption The fluid is in a rapidly rotating regime where Coriolis forces dominate vertical motions.
    Stated directly as the condition for the turbulence studied.

pith-pipeline@v0.9.0 · 5443 in / 1424 out tokens · 50747 ms · 2026-05-10T16:04:40.732577+00:00 · methodology

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Reference graph

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