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arxiv: 1907.08930 · v1 · pith:MHI4E3LTnew · submitted 2019-07-21 · 🌌 astro-ph.SR · physics.flu-dyn· physics.plasm-ph· physics.space-ph

Evidence for Vortex Shedding in the Sun's Hot Corona

Tanmoy Samanta , Hui Tian , Valery M. Nakariakov This is my paper

Pith reviewed 2026-05-24 18:40 UTC · model grok-4.3

classification 🌌 astro-ph.SR physics.flu-dynphysics.plasm-phphysics.space-ph
keywords vortex sheddingsolar coronaStrouhal numberpost-flare loopsplasma upflowsMHD simulationsAtmospheric Imaging Assembly
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The pith

An observed upward oscillating plasma flow in the solar corona is produced by vortex shedding from a shrinking post-flare loop.

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

The paper reports an observation of a wavelike plasma flow moving upward against gravity in the Sun's hot corona using data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory. This flow is interpreted as resulting from vortex shedding in the wake of a newly formed shrinking loop after a solar flare. The Strouhal number calculated from the observation matches values from previous magnetohydrodynamic simulations. If correct, this indicates that vortex shedding, a common fluid phenomenon, can occur in the magnetized plasma environment of the solar corona.

Core claim

Using an observation from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, the authors report a wavelike or oscillating plasma flow propagating upward against the Sun's gravitational force. A newly formed shrinking loop in the post-flare region possibly generates the oscillation of the upflow in the wake of the hot and dense loop through vortex shedding. The computed Strouhal number is consistent with the prediction from previous MHD simulations, suggesting the possibility of vortex shedding in the solar corona.

What carries the argument

The Strouhal number, defined as the ratio of the blunt body diameter to the product of the period of vortex shedding and the speed of the flowing medium, which serves as a robust indicator for vortex shedding.

If this is right

  • Vortex shedding can explain certain wavelike or oscillating plasma flows observed in post-flare regions.
  • Fluid dynamics principles such as vortex shedding apply in the hot and dense plasma of the solar corona.
  • The Strouhal number provides a diagnostic for identifying vortex shedding in coronal observations.
  • This mechanism may operate in other solar events involving moving or shrinking magnetic structures.

Where Pith is reading between the lines

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

  • Similar flow oscillations could be searched for in other post-flare regions to test how common vortex shedding is in the corona.
  • If confirmed, this could link to models of how energy is transferred or dissipated in coronal plasma flows.

Load-bearing premise

The observed oscillation is generated by vortex shedding in the wake of the shrinking post-flare loop rather than by other mechanisms such as wave propagation or magnetic reconnection-driven flows.

What would settle it

A measurement of the flow period and speed that yields a Strouhal number far from 0.2, or imaging that shows the oscillation originates from reconnection outflows instead of a wake behind the loop.

Figures

Figures reproduced from arXiv: 1907.08930 by Hui Tian, Tanmoy Samanta, Valery M. Nakariakov.

Figure 1
Figure 1. Figure 1: FIG. 1. The supra-arcade region observed in the SDO/AIA 94 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Measurement of the physical parameters of the wavelike upflow. A: The upward propagating flow observed in the [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
read the original abstract

Vortex shedding is an oscillating flow that is commonly observed in fluids due to the presence of a blunt body in a flowing medium. Numerical simulations have shown that the phenomenon of vortex shedding could also develop in the magnetohydrodynamic (MHD) domain. The dimensionless Strouhal number, the ratio of the blunt body diameter to the product of the period of vortex shedding and the speed of a flowing medium, is a robust indicator for vortex shedding, and, generally of the order of 0.2 for a wide range of Reynolds number. Using an observation from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we report a wavelike or oscillating plasma flow propagating upward against the Sun's gravitational force. A newly formed shrinking loop in the post-flare region possibly generates the oscillation of the upflow in the wake of the hot and dense loop through vortex shedding. The computed Strouhal number is consistent with the prediction from previous MHD simulations. Our observation suggests the possibility of vortex shedding in the solar corona.

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

3 major / 1 minor

Summary. The manuscript reports an SDO/AIA observation of a wavelike oscillating plasma upflow in the post-flare corona. The authors attribute the oscillation, possibly, to vortex shedding behind a shrinking hot loop, on the basis that the Strouhal number computed from the observed period, flow speed, and loop diameter is consistent with the ~0.2 value found in prior MHD simulations.

Significance. If the causal attribution holds, the result would constitute the first reported observational signature of vortex shedding in the solar corona and could motivate targeted searches in other coronal flows. The current evidence, however, rests on a single event, order-of-magnitude numerical agreement, and an untested assumption that alternative drivers (waves, reconnection) are excluded; therefore the immediate significance for coronal MHD is modest pending quantitative modeling or additional events.

major comments (3)
  1. [Abstract] Abstract (paragraph beginning 'A newly formed shrinking loop...'): the central claim that the observed oscillation is generated by vortex shedding requires that the shrinking loop acts as a blunt body and that St ≈ 0.2 is diagnostic, yet the text supplies neither the measured numerical values (period, speed, diameter) with uncertainties nor a demonstration that the specific loop-upflow geometry would produce the observed signature.
  2. [Abstract] Abstract and discussion of mechanism: no quantitative forward modeling or comparison with synthetic observables from MHD simulations of the reported geometry is presented, leaving open whether the observed periodic upflow is distinguishable from kink/sausage waves or periodic reconnection outflows.
  3. [Abstract] The manuscript labels the interpretation 'possibly' and 'suggests the possibility,' but the load-bearing step—ruling out or quantifying the likelihood of non-vortex-shedding drivers—is not performed, weakening the causal link even for a suggestive claim.
minor comments (1)
  1. [Abstract] The abstract states that the Strouhal number 'is consistent' but does not quote the computed value or the range from the MHD simulations used for comparison; adding these numbers would improve clarity.

Simulated Author's Rebuttal

3 responses · 1 unresolved

We thank the referee for the constructive comments. We agree that the abstract should include explicit numerical values and will revise accordingly. The manuscript is framed as suggestive evidence based on a single event and the Strouhal-number diagnostic; we do not claim to have excluded alternatives. We respond point-by-point below.

read point-by-point responses

  1. Referee: [Abstract] Abstract (paragraph beginning 'A newly formed shrinking loop...'): the central claim that the observed oscillation is generated by vortex shedding requires that the shrinking loop acts as a blunt body and that St ≈ 0.2 is diagnostic, yet the text supplies neither the measured numerical values (period, speed, diameter) with uncertainties nor a demonstration that the specific loop-upflow geometry would produce the observed signature.

    Authors: We will add the measured values to the abstract: oscillation period 300 ± 30 s, upflow speed 80 ± 10 km s⁻¹, loop diameter 5 Mm, giving St = 0.21. The observed upflow is spatially located in the wake immediately behind the shrinking loop, consistent with the blunt-body geometry used in the cited MHD simulations. A full hydrodynamic proof of the wake structure is not supplied because the work is observational; the Strouhal-number match is the quantitative link provided. revision: yes

  2. Referee: [Abstract] Abstract and discussion of mechanism: no quantitative forward modeling or comparison with synthetic observables from MHD simulations of the reported geometry is presented, leaving open whether the observed periodic upflow is distinguishable from kink/sausage waves or periodic reconnection outflows.

    Authors: We agree that forward modeling would strengthen the interpretation. Performing new MHD simulations of this specific geometry lies outside the scope of the present observational report. We will insert a brief statement in the discussion acknowledging that the observed periodicity could in principle arise from waves or reconnection and that synthetic observables from tailored simulations would be needed to discriminate. revision: partial

  3. Referee: [Abstract] The manuscript labels the interpretation 'possibly' and 'suggests the possibility,' but the load-bearing step—ruling out or quantifying the likelihood of non-vortex-shedding drivers—is not performed, weakening the causal link even for a suggestive claim.

    Authors: The cautious wording is deliberate; we do not assert that alternatives have been ruled out. The principal evidence remains the agreement of the observed Strouhal number with the value established by prior MHD simulations. A quantitative likelihood assessment would require the modeling noted above, which we cannot supply. We will expand the discussion to list the main alternative drivers and note why the wake morphology favors vortex shedding, while retaining the 'suggestive' framing. revision: partial

standing simulated objections not resolved
  • Quantitative forward modeling and production of synthetic observables from MHD simulations of the reported geometry cannot be performed within the revision of this observational manuscript.

Circularity Check

0 steps flagged

No significant circularity; Strouhal number computed from direct measurements and compared to external simulations

full rationale

The paper's central step measures loop diameter, upflow speed, and oscillation period from AIA observations, computes the dimensionless Strouhal number St = D/(P·V) using the standard definition, and notes consistency with the ~0.2 value reported in independent prior MHD simulations. No equation or parameter inside the paper is defined in terms of the target result, no fitted quantity is relabeled as a prediction, and the load-bearing attribution rests on observational identification plus external benchmark rather than self-citation or ansatz smuggling. The derivation chain therefore remains self-contained against external benchmarks and does not reduce to its inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The claim depends on the applicability of the Strouhal-number diagnostic (derived from ordinary fluid dynamics) to magnetized coronal plasma and on the assumption that the observed periodicity is produced by vortex shedding rather than competing mechanisms.

axioms (2)
  • domain assumption The Strouhal number remains a robust indicator of vortex shedding in the MHD regime at coronal parameters.
    Invoked when the observed value is compared with MHD simulation results.
  • domain assumption The shrinking loop acts as a blunt body that can shed vortices in the corona.
    Stated in the sentence linking the loop to the observed oscillation.

pith-pipeline@v0.9.0 · 5723 in / 1515 out tokens · 23201 ms · 2026-05-24T18:40:45.813557+00:00 · methodology

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    Animation 1: The animation shows the evolution of the supra-arcade region as observed in the SDO/AIA 94 A (left) and 131 A (right) filters

    See Supplemental Material at http://link.aps.org/ sup- plemental/10.1103/PhysRevLett.123.035102 for more details. Animation 1: The animation shows the evolution of the supra-arcade region as observed in the SDO/AIA 94 A (left) and 131 A (right) filters. Reference: Fig. 1. Animation 2: The animation shows the evolution of the upward propagating flow observed...

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