Spine-fan reconnection

Wyper, P. F.; Jain, Rekha; Pontin, D. I.

doi:10.1051/0004-6361/201219281

Cited by 11 publications

(9 citation statements)

References 38 publications

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“…On the other hand, the strength of the magnetic field along the loops does not take into account the magnetic topology, which necessarily influences the heating as well (formation of separatrices, preferential reconnection sites; e.g., Aly & Amari 1997;Pariat et al 2009;Parnell et al 2010;Wyper et al 2012). The heating parameter-space scan for loopB shows that we can produce TNE cycles for this loop geometry only with asymmetric heating profiles.…”

Section: Exploration De-correlated From the Magnetic Field Strengthmentioning

confidence: 99%

On the Occurrence of Thermal Nonequilibrium in Coronal Loops

Froment

Auchère

Mikić

et al. 2018

ApJ

100

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Long-period EUV pulsations, recently discovered to be common in active regions, are understood to be the coronal manifestation of thermal nonequilibrium (TNE). The active regions previously studied with EIT/Solar and Heliospheric Observatory and AIA/SDO indicated that long-period intensity pulsations are localized in only one or two loop bundles. The basic idea of this study is to understand why. For this purpose, we tested the response of different loop systems, using different magnetic configurations, to different stratifications and strengths of the heating. We present an extensive parameter-space study using 1D hydrodynamic simulations (1020 in total) and conclude that the occurrence of TNE requires specific combinations of parameters. Our study shows that the TNE cycles are confined to specific ranges in parameter space. This naturally explains why only some loops undergo constant periodic pulsations over several days: since the loop geometry and the heating properties generally vary from one loop to another in an active region, only the ones in which these parameters are compatible exhibit TNE cycles. Furthermore, these parameters (heating and geometry) are likely to vary significantly over the duration of a cycle, which potentially limits the possibilities of periodic behavior. This study also confirms that long-period intensity pulsations and coronal rain are two aspects of the same phenomenon: both phenomena can occur for similar heating conditions and can appear simultaneously in the simulations.

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Section: Exploration De-correlated From the Magnetic Field Strengthmentioning

confidence: 99%

On the Occurrence of Thermal Nonequilibrium in Coronal Loops

Froment

Auchère

Mikić

et al. 2018

ApJ

100

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“…Based on the theoretical models, a series of numerical experiments are conducted through applying perturbations, like rotational and shearing motions, to the spine and fan structures extended from the null. As a result, strong current is found to develop around the null-point (Pontin & Galsgaard 2007;Galsgaard & Pontin 2011;Wyper et al 2012). Pontin et al (2013) demonstrated that the connectivity of the magnetic field line would change when it transfers across the CS forming around the null-point and treat that as a feature of spine-fan reconnection.…”

Section: Introductionmentioning

confidence: 99%

Observation of Magnetic Reconnection at a 3d Null Point Associated With a Solar Eruption

Sun

Zhang

Yang

et al. 2016

ApJL

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Magnetic null has long been recognized as a special structure serving as a preferential site for magnetic reconnection (MR). However, the direct observational study of MR at null-points is largely lacking. Here, we show the observations of MR around a magnetic null associated with an eruption that resulted in an M1.7 flare and a coronal mass ejection. The GOES Xray profile of the flare exhibited two peaks at ∼02:23 UT and ∼02:40 UT on 2012 November 8, respectively. Based on the imaging observations, we find that the first and also primary Xray peak was originated from MR in the current sheet underneath the erupting magnetic flux rope (MFR). On the other hand, the second and also weaker X-ray peak was caused by MR around a null-point located above the pre-eruption MFR. The interaction of the null-point and the erupting MFR can be described as a two-step process. During the first step, the erupting and fast expanding MFR passed through the null-point, resulting in a significant displacement of the magnetic field surrounding the null. During the second step, the displaced magnetic field started to move back, resulting in a converging inflow and subsequently the MR around the null. The null-point reconnection is a different process from the current sheet reconnection in this flare; the latter is the cause of the main peak of the flare, while the former is the cause of the secondary peak of the flare and the conspicuous high-lying cusp structure.

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“…Similarly, the simplicity of the driver used here is unlikely to reflect the true nature of drivers in the real solar corona. The impact of driver complexity on spine-fan reconnection specifically has been investigated by Wyper et al (2012) who, however, focus on sheared drivers, as opposed to the torsional drivers employed here. It would be of interest to understand how different magnetic field configurations and forms of driver affect the formation and stability of the kind of current-vortex sheets studied here.…”

Section: Discussionmentioning

confidence: 99%

Kelvin-Helmholtz instability and collapse of a twisted magnetic null point with anisotropic viscosity

Quinn

MacTaggart

Simitev

2021

A&A

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Context. Magnetic null points are associated with high-energy coronal phenomena such as solar flares and are often sites of reconnection and particle acceleration. Dynamic twisting of a magnetic null point can generate a Kelvin-Helmholtz instability (KHI) within its fan plane and can instigate spine-fan reconnection and an associated collapse of the null point under continued twisting. Aims. This article aims to compare the effects of isotropic and anisotropic viscosity in simulations of the KHI and collapse in a dynamically twisted magnetic null point. Methods. We performed simulations using the 3D magnetohydrodynamics code Lare3d with a custom anisotropic viscosity module. A pair of high-resolution simulations were performed, one using isotropic viscosity and another using anisotropic viscosity, keeping all other factors identical. We analysed the results in detail. A further parameter study was performed over a range of values for viscosity and resistivity. Results. Both viscosity models permit the growth of the KHI and the eventual collapse of the null point. Over all studied parameters, anisotropic viscosity allows a faster growing instability, while isotropic viscosity damps the instability to the extent of stabilisation in some cases. Although the viscous heating associated with anisotropic viscosity is generally smaller, the ohmic heating dominates and is enhanced by the current sheets generated by the instability. This leads to a greater overall heating rate when using anisotropic viscosity. The collapse of the null point occurs significantly sooner when anisotropic viscosity is employed.

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Spine-fan reconnection

Cited by 11 publications

References 38 publications

On the Occurrence of Thermal Nonequilibrium in Coronal Loops

On the Occurrence of Thermal Nonequilibrium in Coronal Loops

Observation of Magnetic Reconnection at a 3d Null Point Associated With a Solar Eruption

Kelvin-Helmholtz instability and collapse of a twisted magnetic null point with anisotropic viscosity

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