Current-sheet Oscillations Caused by the Kelvin–Helmholtz Instability at the Loop Top of Solar Flares

Wang, Yulei; Cheng, Xin; Ren, Zining; Ding, M. D.

doi:10.3847/2041-8213/ac715a

Cited by 8 publications

(9 citation statements)

References 52 publications

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“…Magnetic reconnection essentially takes place at small scales down to tens of metres in the corona. The large-scale current sheet during solar eruptions is conjectured to be composed of fragmented current elements (or magnetic islands) of different scales, likely arising from tearing mode instability and turbulence [16][17][18][19][20] . Intermittent sunward outflow jets with a wide velocity distribution provide a strong indicator of fragmention of the large-scale current sheet 4 .…”

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confidence: 99%

Ultra-high-resolution observations of persistent null-point reconnection in the solar corona

Cheng

Priest

et al. 2023

Nat Commun

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Magnetic reconnection is a key mechanism involved in solar eruptions and is also a prime possibility to heat the low corona to millions of degrees. Here, we present ultra-high-resolution extreme ultraviolet observations of persistent null-point reconnection in the corona at a scale of about 390 km over one hour observations of the Extreme-Ultraviolet Imager on board Solar Orbiter spacecraft. The observations show formation of a null-point configuration above a minor positive polarity embedded within a region of dominant negative polarity near a sunspot. The gentle phase of the persistent null-point reconnection is evidenced by sustained point-like high-temperature plasma (about 10 MK) near the null-point and constant outflow blobs not only along the outer spine but also along the fan surface. The blobs appear at a higher frequency than previously observed with an average velocity of about 80 km s−1 and life-times of about 40 s. The null-point reconnection also occurs explosively but only for 4 minutes, its coupling with a mini-filament eruption generates a spiral jet. These results suggest that magnetic reconnection, at previously unresolved scales, proceeds continually in a gentle and/or explosive way to persistently transfer mass and energy to the overlying corona.

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confidence: 99%

Ultra-high-resolution observations of persistent null-point reconnection in the solar corona

Cheng

Priest

et al. 2023

Nat Commun

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“…Peaks in turbulence velocity values tend to show up above the high-density flare loops, reaching 100 km s −1 -200 km s −1 , while footpoints have lower turbulent velocities of a few tens of km s −1 . Turbulence has been frequently reproduced in 2D simulations, but the obtained turbulence is more localized (e.g., Fang et al 2016;Ruan et al 2018;Ye et al 2019;Wang et al 2022). Wang et al (2022) invoke the Kelvin-Helmholtz instability (KHI) in their 2D settings to explain the observed wiggling of the current sheet above.…”

Section: Introductionmentioning

confidence: 99%

“…Turbulence has been frequently reproduced in 2D simulations, but the obtained turbulence is more localized (e.g., Fang et al 2016;Ruan et al 2018;Ye et al 2019;Wang et al 2022). Wang et al (2022) invoke the Kelvin-Helmholtz instability (KHI) in their 2D settings to explain the observed wiggling of the current sheet above. In contributions to solar flare research, we investigated (Ruan et al 2020) the interplay between 2D magnetohydrodynamic (MHD) flare evolutions as coupled to analytic prescriptions of the accelerated electron beams, where we could reproduce both HXR source regions, and evolve the flare far into the postflare regime to reproduce flare-driven coronal rain (Ruan et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Magnetohydrodynamic Turbulence Formation in Solar Flares: 3D Simulation and Synthetic Observations

Ruan¹,

Yan

Keppens³

2023

ApJ

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Turbulent plasma motion is common in the universe and invoked in solar flares to drive effective acceleration leading to high-energy electrons. Unresolved mass motions are frequently detected in flares from extreme ultraviolet (EUV) observations, which are often regarded as turbulence. However, how this plasma turbulence forms during the flare is still largely a mystery. Here we successfully reproduce observed turbulence in our 3D magnetohydrodynamic simulation where the magnetic reconnection process is included. The turbulence forms as a result of an intricate nonlinear interaction between the reconnection outflows and the magnetic arcades below the reconnection site, in which the shear-flow-driven Kelvin–Helmholtz instability (KHI) plays a key role in generating turbulent vortices. The turbulence is produced above high-density flare loops and then propagates to chromospheric footpoints along the magnetic field as Alfvénic perturbations. High turbulent velocities above 200 km s−1 can be found around the termination shock, while the low atmosphere reaches turbulent velocities of 10 km s−1 at a layer where the number density is about 1011 cm−3. The turbulent region with maximum nonthermal velocity coincides with the region where the observed high-energy electrons are concentrated, demonstrating the potential role of turbulence in acceleration. Synthetic views in EUV and fitted Hinode-EUV Imaging Spectrometer spectra show excellent agreement with observational results. An energy analysis demonstrates that more than 10% of the reconnection-downflow kinetic energy can be converted to turbulent energy via KHI.

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“…The optically thin radiative cooling term = L R n n T e i ( ) is based on a widely used model in which n e and n i are, respectively, the number density of electrons and ions, and L T ( ) is a piece-wise cooling function (Klimchuk et al 2008) to eliminate the effects of cooling and heating in the region below y = 0.2. In our simulation, all physical quantities are normalized based on the same dimensionless units as Wang et al (2022).…”

Section: Numerical Modelmentioning

confidence: 99%

Three-dimensional Turbulent Reconnection within the Solar Flare Current Sheet

Wang,

Cheng,

Ding

et al. 2023

ApJL

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Solar flares can release coronal magnetic energy explosively and may impact the safety of near-Earth space environments. Their structures and properties on the macroscale have been interpreted successfully by the generally accepted 2D standard model, invoking magnetic reconnection theory as the key energy conversion mechanism. Nevertheless, some momentous dynamical features as discovered by recent high-resolution observations remain elusive. Here, we report a self-consistent high-resolution 3D magnetohydrodynamical simulation of turbulent magnetic reconnection within a flare current sheet. It is found that fragmented current patches of different scales are spontaneously generated with a well-developed turbulence spectrum at the current sheet, as well as at the flare loop-top region. The close coupling of tearing mode and Kelvin–Helmholtz instabilities plays a critical role in developing turbulent reconnection and in forming dynamical structures with synthetic observables in good agreement with realistic observations. The sophisticated modeling makes a paradigm shift from the traditional to a 3D turbulent reconnection model unifying flare dynamical structures of different scales.

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Current-sheet Oscillations Caused by the Kelvin–Helmholtz Instability at the Loop Top of Solar Flares

Cited by 8 publications

References 52 publications

Ultra-high-resolution observations of persistent null-point reconnection in the solar corona

Ultra-high-resolution observations of persistent null-point reconnection in the solar corona

Magnetohydrodynamic Turbulence Formation in Solar Flares: 3D Simulation and Synthetic Observations

Three-dimensional Turbulent Reconnection within the Solar Flare Current Sheet

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