Flow Instabilities in Solar Jets in Their Upstream and Downstream Regimes

Li, Xiaohong; Zhang, Jun; Yang, Shuhong; Hou, Yijun

doi:10.3847/1538-4357/ab0f39

Cited by 16 publications

(16 citation statements)

References 61 publications

(68 reference statements)

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“…These authors considered that the strong transverse velocity shear between the light bridge and the umbrae triggered the Kelvin-Helmholtz instability (KHI) resulting in the vortex structures, which then launched the jet in the vertical direction through magnetic reconnection or waves. To our knowledge, velocity shear larger than (it would be twice under certain assumptions) the local Alfvén speed (here ∼10 km s −1 in the photosphere) is needed for KHI to take place (Chandrasekhar 1961;Li et al 2019). Also, the KHI-induced vortices would form randomly at the boundary of flows (here the boundary is the edge of the light bridge).…”

Section: Summary and Discussionmentioning

confidence: 98%

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

Hou

Zhong

et al. 2020

A&A

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Context. Penumbral filaments and light bridges are prominent structures inside sunspots and are important for understanding the nature of sunspot magnetic fields and magneto-convection underneath. Aims. We investigate an interesting event where several penumbral filaments intrude into a sunspot light bridge. In doing so we aim to gain further insight into the magnetic fields of the sunspot penumbral filament and light bridge, as well as their interaction. Methods. Combining data from the New Vacuum Solar Telescope, Solar Dynamics Observatory, and Interface Region Imaging Spectrograph, we study the emission, kinematic, and magnetic topology characteristics of the penumbral filaments intruding into the light bridge and the resultant jets. Results. At the west part of the light bridge, the intruding penumbral filaments penetrate into the umbrae on both sides of the light bridge, and two groups of jets are also detected. The jets share the same projected morphology with the intruding filaments and are accompanied by intermittent footpoint brightenings. Simultaneous spectral imaging observations provide convincing evidence for the presences of magnetic-reconnection-related heating and bidirectional flows near the jet bases and contribute to measuring the vector velocities of the jets. Additionally, nonlinear force-free field extrapolation results reveal strong and highly inclined magnetic fields along the intruding penumbral filaments, highly consistent with the results deduced from the vector velocities of the jets. Therefore, we propose that the jets could be caused by magnetic reconnections between emerging fields within the light bridge and the nearly horizontal fields of intruding filaments. The jets are then ejected outward along the stronger filament fields. Conclusions. Our study indicates that magnetic reconnection could occur between the penumbral filament fields and emerging fields within the light bridge and produce jets along the stronger filament fields. These results further complement the study of magnetic reconnection and dynamic activities within the sunspot.

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Section: Summary and Discussionmentioning

confidence: 98%

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

Hou

Zhong

et al. 2020

A&A

Self Cite

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“…And the KHI-induced vortices would form randomly at the boundary of flows (here is the edge of the light bridge). Considering the actual observations in both events reported in Yang et al (2019) and our study, we speculate that the vortices could be caused by the interaction between the large-scale, longlasting horizontal flows and some small-scale local convection cells (Toriumi et al 2015a) at some sites of the bridge during its developing phase, when the local convections are relatively stronger than that in the mature (or decaying) bridges. The diverging flows caused by the small-scale local convection would block the large-scale horizontal flows along the bridge filaments at some sites and squeeze them (also the magnetic fields) outwards, which then simultaneously intrude into the umbrae and form the vortex structures at both sides of the bridge.…”

Section: Summary and Discussionmentioning

confidence: 55%

“…These authors considered that the strong transverse velocity shear between the light bridge and the umbrae triggered the Kelvin-Helmholtz instability (KHI) resulting in the vortex structures, which then launched the jet in the vertical direction through magnetic reconnection or waves. To our knowledge, the velocity shear larger than (it would be twice under certain assumptions) local Alfvén speed (here is 10 km s −1 in the photosphere) is needed to make KHI take place (Chandrasekhar 1961;Li et al 2019). And the KHI-induced vortices would form randomly at the boundary of flows (here is the edge of the light bridge).…”

Section: Summary and Discussionmentioning

confidence: 99%

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

Hou,

Li,

Zhong

et al. 2020

Preprint

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Context. Penumbral filaments and light bridges are prominent structures inside sunspots and are important for understanding the nature of sunspot magnetic fields and magneto-convection underneath. Aims. We investigate an interesting event where several penumbral filaments intruded into a sunspot light bridge for more insights into magnetic fields of the sunspot penumbral filament and light bridge, as well as their interaction. Methods. Combining data from the New Vacuum Solar Telescope, Solar Dynamics Observatory, and Interface Region Imaging Spectrograph, we study the emission, kinematic, and magnetic topology characteristics of the penumbral filaments intruding into the light bridge and the resultant jets. Results. At the west part of the light bridge, the intruding penumbral filaments penetrated into the umbrae on both sides of the light bridge, and two groups of jets were also detected. The jets shared the same projected morphology with the intruding filaments and were accompanied by intermittent footpoint brightenings. Simultaneous spectral imaging observations provide convincing evidences for the presences of magnetic reconnection related heating and bidirectional flows near the jet bases and contribute to measuring vector velocities of the jets. Additionally, nonlinear force-free field extrapolation results reveal strong and highly inclined magnetic fields along the intruding penumbral filaments, consistent well with the results deduced from the vector velocities of the jets. Therefore, we propose that the jets could be caused by magnetic reconnections between emerging fields within the light bridge and the nearly horizontal fields of intruding filaments. They were then ejected outward along the stronger filaments fields. Conclusions. Our study indicates that magnetic reconnection could occur between the penumbral filament fields and emerging fields within light bridge and produce jets along the stronger filament fields. These results further complement the study of magnetic reconnection and dynamic activities within the sunspot.

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“…The simplest is the basic flow of two fluids in par-allel infinite streams of different velocities, which is subject to Kelvin-Helmholtz instability (Helmholtz 1868;Kelvin 1871). Kelvin-Helmhotz instability has been intensively observed in the solar atmosphere at boundaries of rising coronal mass ejections (Ofman & Thompson 2011;Foullon et al 2011Foullon et al , 2013Möstl et al 2013), in solar prominences (Berger et al 2010;Ryutova et al 2010) and in jets (Zhelyazkov et al 2015(Zhelyazkov et al , 2018Li et al 2019). Various types of flows with smooth transverse profiles are also unstable in certain conditions (Drazin & Reid 1981).…”

Section: Introductionmentioning

confidence: 99%

Kink instability of triangular jets in the solar atmosphere

Zaqarashvili,

Lomineishvili,

Leitner

et al. 2021

Preprint

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Context. It is known that hydrodynamic triangular jets (i. e. the jet with maximal velocity at its axis, which linearly decreases at both sides) are unstable to antisymmetric kink perturbations. The inclusion of magnetic field may lead to the stabilisation of the jets. Jets and complex magnetic fields are ubiquitous in the solar atmosphere, which suggests the possibility of the kink instability in certain cases.Aims. The aim of the paper is to study the kink instability of triangular jets sandwiched between magnetic tubes/slabs and its possible connection to observed properties of the jets in the solar atmosphere. Methods. A dispersion equation governing the kink perturbations is obtained through matching of analytical solutions at the jet boundaries. The equation is solved analytically and numerically for different parameters of jets and surrounding plasma. The analytical solution is accompanied by a numerical simulation of fully nonlinear MHD equations for a particular situation of solar type II spicules. Results. MHD triangular jets are unstable to the dynamic kink instability depending on the Alfvén Mach number (the ratio of flow to Alfvén speeds) and the ratio of internal and external densities. When the jet has the same density as the surrounding plasma, then only super Alfvénic flows are unstable. However, denser jets are unstable also in sub Alfvénic regime. Jets with an angle to the ambient magnetic field have much lower thresholds of instability than field-aligned flows. Growth times of the kink instability are estimated as 6-15 min for type I spicules and 5-60 s for type II spicules matching with their observed life times. Numerical simulation of full nonlinear equations shows that the transverse kink pulse locally destroys the jet in less than a minute in the conditions of type II spicules.Conclusions. Dynamic kink instability may lead to full breakdown of MHD flows and consequently to observed disappearance of spicules in the solar atmosphere.

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Flow Instabilities in Solar Jets in Their Upstream and Downstream Regimes

Cited by 16 publications

References 61 publications

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

Kink instability of triangular jets in the solar atmosphere

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