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arxiv: 2512.19942 · v1 · submitted 2025-12-23 · 🌌 astro-ph.SR

Recognition: no theorem link

Observation of Large-Scale Kelvin-Helmholtz Instability Wave Driven by a Coronal Mass Ejection

Leon Ofman , Olga Khabarova , Ryun-Yong Kwon , Yogesh , Eyal Heifetz , Katariina Nykyri
Authors on Pith no claims yet

Pith reviewed 2026-05-16 20:48 UTC · model grok-4.3

classification 🌌 astro-ph.SR
keywords Kelvin-Helmholtz instabilitycoronal mass ejectionupper coronavorticesAlfvén speedParker Solar Probesolar wind turbulence
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The pith

A fast coronal mass ejection triggered large-scale Kelvin-Helmholtz waves that rolled into vortices between 6 and 14 solar radii.

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

The paper presents the first clear observation of large-scale Kelvin-Helmholtz instability waves in the upper corona, captured during the passage of a fast CME on 2024 February 16. These waves began in the linear stage and developed into the nonlinear regime with visible vortices along the CME flank. The driving mechanism is the CME radial speed exceeding the local Alfvén speed, which created favorable shear conditions including stretched magnetic field lines and lowered density. A second CME arriving shortly afterward further amplified the fully nonlinear waves. The observed wave growth rate matches theoretical expectations for magnetized plasma, showing that such events can occur and be detected with existing coronagraphs when the right speed and field conditions align.

Core claim

We report the event with large-scale KHI waves observed from ∼6 to 14 R⊙ on 2024-Feb-16 using SOHO/LASCO and STEREO-A coronagraphs. KHI appeared during the passage of a fast CME and evolved into the nonlinear stage showing evidence of vortices. A closely timed subsequent CME in the same region has further developed the fully nonlinear KHI waves along its flank. We find that the radial speed of the CMEs exceeds the estimated local Alfven speed obtained from in-situ Parker Solar Probe (PSP) magnetic field data at perihelia. We propose that such events are rare because the fast CME created specific conditions favorable for instability growth in its trailing edge, including radial elongation of磁

What carries the argument

Kelvin-Helmholtz instability waves that grow when a fast CME's radial speed exceeds the local Alfvén speed, producing linear waves that roll up into vortices at the shear interface along the CME flank.

If this is right

  • KHI waves contribute to turbulence and dissipation in the upper corona and solar wind.
  • Nonlinear vortex formation becomes visible in coronagraph images once the instability reaches large amplitudes.
  • A second fast CME passing the same region can push the waves into a fully developed nonlinear state.
  • The growth rate of the observed waves is consistent with linear theory for magnetized shear flows.
  • Such events require a fast CME that stretches field lines and reduces density behind its leading edge.

Where Pith is reading between the lines

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

  • Similar shear-driven instabilities may occur more often in the heliosphere if coronagraph coverage extends farther out during high-speed events.
  • Numerical simulations initialized with the observed CME speed and field geometry could predict the exact vortex sizes seen in the images.
  • The enhanced mixing from these vortices could affect the radial transport of energetic particles along the CME flank.
  • Repeated observations with higher-cadence imaging would allow direct measurement of the instability growth time.

Load-bearing premise

The observed structures are identified as KHI because of their wavy morphology in coronagraph images and because the CME speed is faster than an estimated local Alfvén speed that depends on assumed values for density and magnetic-field strength.

What would settle it

In-situ measurements at the wave location showing that the actual local speed remains below the Alfvén speed calculated from simultaneous density and magnetic-field data would show the structures are not KHI.

Figures

Figures reproduced from arXiv: 2512.19942 by Eyal Heifetz, Katariina Nykyri, Leon Ofman, Olga Khabarova, Ryun-Yong Kwon, Yogesh.

Figure 1
Figure 1. Figure 1: The CME and the associated wave marked with the yellow arrow observed on 2024 February 16. The timing of the various instruments are indicated on the panels. (a) STEREO Cor 2 (the inner regions are obtained from EUVI and Cor 1 images). (b) The SOHO/LASCO C3 observations (the inner regions are obtained from LASCO C2, C3 and SDO AIA 193˚A images). The animations of this event produced by JHelioviewer (see, h… view at source ↗
Figure 2
Figure 2. Figure 2: (a) Portion of the STEREO COR2-A field of view at 16:38 UT on 2024 February 16, highlighting the KHI wave event. The two vertical dashed and solid lines refer to the two virtual slit positions used to construct the distance–time plots in panels (b) and (c). The position of Slit 1 (dashed line) is fixed, while Slit 2 (solid line) crosses the KHI wave features. Colored dots along Slit 2 mark the locations us… view at source ↗
Figure 3
Figure 3. Figure 3: Five snapshots from the STEREO Cor 1 animation of the KHI feature shown Figure 2a at hourly intervals starting at 13:07 UT on 2024 February 16 showing the development of the KHI wave structure and the developed stage of KHI waves and vortices with their locations marked with yellow arrows. (a) (b) (c) Wavelength 0 5 10 15 20 25 Hours (starting from 2024-02-16 00:07:45 UT) 0 1 2 3 4 Wavelength [Solar Radii]… view at source ↗
Figure 4
Figure 4. Figure 4: (a) The temporal evolution of the wavelength of the KHI wave observed on 2024 February 16 by STEREO COR2 A, determined as shown at Slit 2 in Figure 2b. The temporal evolution of the velocities: (b) The radial velocities of the features along Slit 1 (#1 solid, #2 dashes, #3 dots) and (c) the evolution of velocities along Slit 2 (#1 solid, #2 dashes, #3 dots, #4 dot-dashes). The line styles are the same as i… view at source ↗
Figure 5
Figure 5. Figure 5: The statistical distribution vs. heliocentric distance obtained from PSP in the range 10-30 Rs obtained from encounters 4-23. (a) The Alfv´en speed with power-law fit; (b) radial solar wind speed with N. R. Sheeley et al. (1997) fit. The dashed vertical line marks the mean Alfv´en critical surface at 16.5 Rs where MA = 1. The color bar shows the number of counts. The black lines show the fits and the fit p… view at source ↗
read the original abstract

The Kelvin-Helmholtz instability (KHI) can occur when there is a relative motion between two adjacent fluids. In the case of magnetized plasma, the shear velocity must exceed the local Alfv\'{e}n speed for the instability to develop. The KHI produces nonlinear waves that eventually roll up into vortices and contribute to turbulence and dissipation. In the solar atmosphere KHI has been detected in coronal mass ejections (CMEs), jets, and prominences, mainly in the low corona. Only a few studies have reported the KHI in the upper corona, and its vortex development there has not been previously observed. We report the event with large-scale KHI waves observed from $\sim 6$ to 14~$R_{\odot}$ on 2024-Feb-16 using SOHO/LASCO and STEREO-A coronagraphs. KHI appeared during the passage of a fast CME and evolved into the nonlinear stage showing evidence of vortices. A closely timed subsequent CME in the same region has further developed the fully nonlinear KHI waves along its flank. We find that the radial speed of the CMEs exceeds the estimated local Alfven speed obtained from in-situ Parker Solar Probe (PSP) magnetic field data at perihelia. We propose that such events are rare because the fast CME created specific conditions favorable for instability growth in its trailing edge, including radial elongation of magnetic-field lines, reduced plasma density, and enhanced velocity and magnetic-field shear along the developing interface. The observed growth rate of KHI wave is in qualitative agreement with the theoretical predictions.

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 / 2 minor

Summary. The manuscript reports the observation of large-scale Kelvin-Helmholtz instability (KHI) waves from approximately 6 to 14 R⊙ on 2024 February 16, driven by a fast CME and observed with SOHO/LASCO and STEREO-A coronagraphs. The waves evolve into the nonlinear regime with vortex formation along the CME flank; a subsequent CME is said to further develop the structures. The authors compare the CME radial speed against the local Alfvén speed estimated from Parker Solar Probe in-situ |B| data (scaled outward) and conclude that the speed exceeds the Alfvén speed, enabling KHI growth under specific trailing-edge conditions (radial field elongation, reduced density, enhanced shear). The observed growth rate is stated to agree qualitatively with theory.

Significance. If the identification and the key instability criterion hold, the result would constitute the first reported detection of nonlinear KHI with vortex roll-up in the upper corona, extending prior low-corona detections and offering direct evidence for KHI-driven turbulence and dissipation at larger heliocentric distances in CMEs.

major comments (3)
  1. [Speed comparison paragraph (near end of abstract and corresponding results section)] The central claim that the CME radial speed exceeds the local Alfvén speed (required for KHI) rests on an assumed density at 6–14 R⊙. The manuscript scales PSP perihelion |B| outward but provides no direct density constraint (e.g., from polarized brightness or white-light inversion) at the wave location; because v_A ∝ 1/√ρ, a factor-of-two density uncertainty can reverse the inequality and invalidate the instability threshold.
  2. [Observation and evolution description] Wave identification and vortex classification are based solely on morphological appearance in coronagraph difference images. No quantitative measurements of wavelength, amplitude, phase speed, or growth rate with uncertainties are reported, nor is an explicit exclusion of alternative interpretations (e.g., Kelvin-Helmholtz-like structures from other shear or projection effects) provided.
  3. [Discussion of growth rate] The statement that the observed growth rate is in qualitative agreement with theoretical predictions lacks a specific calculation, cited dispersion relation, or comparison table; without these, the agreement cannot be evaluated independently.
minor comments (2)
  1. [Figure captions] Figure captions should explicitly label the locations of the reported KHI waves and vortices and indicate the time sequence of the images.
  2. [Abstract] The abstract contains minor typographical inconsistencies in the use of math mode for R_⊙ and Alfvén; these should be standardized in the final version.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the careful and constructive review of our manuscript. We address each major comment below and have revised the manuscript to strengthen the presentation where appropriate.

read point-by-point responses

  1. Referee: [Speed comparison paragraph (near end of abstract and corresponding results section)] The central claim that the CME radial speed exceeds the local Alfvén speed (required for KHI) rests on an assumed density at 6–14 R⊙. The manuscript scales PSP perihelion |B| outward but provides no direct density constraint (e.g., from polarized brightness or white-light inversion) at the wave location; because v_A ∝ 1/√ρ, a factor-of-two density uncertainty can reverse the inequality and invalidate the instability threshold.

    Authors: We acknowledge that the Alfvén speed estimate depends on an assumed density and that direct constraints at the precise wave location are not available from the coronagraph observations. In the revised manuscript we will add a sensitivity analysis using a range of plausible coronal densities (drawn from standard models and scaled PSP data) to show the conditions under which the CME speed exceeds v_A. The central claim will be qualified accordingly while retaining the supporting evidence from the magnetic-field scaling. revision: partial

  2. Referee: [Observation and evolution description] Wave identification and vortex classification are based solely on morphological appearance in coronagraph difference images. No quantitative measurements of wavelength, amplitude, phase speed, or growth rate with uncertainties are reported, nor is an explicit exclusion of alternative interpretations (e.g., Kelvin-Helmholtz-like structures from other shear or projection effects) provided.

    Authors: We agree that quantitative measurements and explicit discussion of alternatives would improve rigor. The revised manuscript will report measured values of wavelength, amplitude, phase speed, and growth rate extracted from the image time series, together with uncertainties. A new paragraph will address potential alternative interpretations (projection effects, other shear flows) and explain why the multi-viewpoint morphology and temporal evolution favor the KHI interpretation. revision: yes

  3. Referee: [Discussion of growth rate] The statement that the observed growth rate is in qualitative agreement with theoretical predictions lacks a specific calculation, cited dispersion relation, or comparison table; without these, the agreement cannot be evaluated independently.

    Authors: We will expand the relevant section to include the explicit growth-rate calculation based on the standard MHD KHI dispersion relation (citing the appropriate reference), together with a direct numerical comparison to the observed value. A small comparison table will be added for clarity. revision: yes

Circularity Check

0 steps flagged

No circularity: observational identification grounded in external data

full rationale

The paper is an observational report identifying KHI waves via coronagraph morphology during a CME and comparing radial speeds to an Alfvén speed estimate drawn from independent PSP magnetic-field measurements. No equations, fitted parameters, or derivations are presented that reduce any claimed result to the input imagery or assumptions by construction. The qualitative agreement with theory is stated without a self-contained derivation chain. The analysis relies on public external datasets and morphological criteria without self-referential definitions or load-bearing self-citations that collapse the central claim.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The claim rests on standard magnetized-plasma assumptions for KHI onset and on the accuracy of Alfvén-speed estimates derived from in-situ data; no new entities or ad-hoc parameters are introduced.

axioms (1)
  • domain assumption KHI develops when velocity shear exceeds the local Alfvén speed in magnetized plasma
    Invoked in the abstract to explain why the fast CME triggered the instability.

pith-pipeline@v0.9.0 · 5613 in / 1241 out tokens · 43418 ms · 2026-05-16T20:48:57.290234+00:00 · methodology

discussion (0)

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