Dynamic accessibility of inflow and outflow reconnective solutions

Tassi, Emanuele; Titov, V. S.; Hornig, G.

doi:10.1063/1.2135768

Cited by 6 publications

(10 citation statements)

References 29 publications

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“…It has been suggested that solutions for spine reconnection in incompressible plasmas [47] may not be dynamically accessible, and while incompressible fan solutions [6] are dynamically accessible [8,[71][72][73], this breaks down when the incompressibility assumption is relaxed [71]. It turns out that the generic null point reconnection mode that is observed in numerical experiments in response to shearing motions is one in which there is a strong fan current with flow across both spine and fan, and which is in some sense a combination of the spine and fan reconnection of Priest and Titov [7].…”

Section: Kinematic Resistive Modelsmentioning

confidence: 99%

Three-dimensional null point reconnection regimes

2009

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Recent advances in theory and computational experiments have shown the need to refine the previous categorisation of magnetic reconnection at three-dimensional null points -points at which the magnetic field vanishes. We propose here a division into three different types, depending on the nature of the flow near the spine and fan of the null. The spine is an isolated field line which approaches the null (or recedes from it), while the fan is a surface of field lines which recede from it (or approach it).So-called torsional spine reconnection occurs when field lines in the vicinity of the fan rotate, with current becoming concentrated along the spine, so that nearby field lines undergo rotational slippage. In torsional fan reconnection field lines near the spine rotate and create a current that is concentrated in the fan with a rotational flux mismatch and rotational slippage. In both of these regimes, the spine and fan are perpendicular and there is no flux transfer across spine or fan. The third regime, called spine-fan reconnection, is the most common in practice and combines elements of the previous spine and fan models. In this case, in response to a generic shearing motion, the null point collapses to form a current sheet that is focused at the null itself, in a sheet that locally spans both the spine and fan. In this regime the spine and fan are no longer perpendicular and there is flux transfer across both of them.

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Section: Kinematic Resistive Modelsmentioning

confidence: 99%

Three-dimensional null point reconnection regimes

2009

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“…Refs. [23,24]). The results of the previous section provide strong evidence that in a fully dynamic and fully 3D (yet incompressible) system, the fan current sheet solutions are indeed dynamically accessible.…”

Section: A Dynamic Accessibilitymentioning

confidence: 99%

Current sheets at three-dimensional magnetic nulls: Effect of compressibility

2007

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The nature of current sheet formation in the vicinity of three-dimensional (3D) magnetic null points is investigated. The particular focus is upon the effect of the compressibility of the plasma on the qualitative and quantitative properties of the current sheet. An initially potential 3D null is subjected to shearing perturbations, as in a previous paper [Pontin et al., Phys. Plasmas, in press (2007)]. It is found that as the incompressible limit is approached, the collapse of the null point is suppressed, and an approximately planar current sheet aligned to the fan plane is present instead. This is the case regardless of whether the spine or fan of the null is sheared. Both the peak current and peak reconnection rate are reduced. The results have a bearing on previous analytical solutions for steady-state reconnection in incompressible plasmas, implying that fan current sheet solutions are dynamically accessible, while spine current sheet solutions are not.In astrophysical plasmas, such as the solar corona, the three-dimensional (3D) magnetic field topology is often highly complex. In such complex 3D magnetic fields, where traditional two-dimensional (2D) X-point magnetic reconnection models may no longer be applicable, determining the sites at which dynamic phenomena and energy release may occur is a crucial and non-trivial problem. Due to the typically very high Lundquist number, such events occur only at locations where intense currents (singular under an ideal MHD evolution) may form.One such site is a 3D magnetic null point (e.g. Refs. [1,2,3,4,5]). The nature of current sheet formation at such 3D nulls is investigated here.3D null points are predicted to be present in abundance in the solar corona (e.g. Refs. [6,7]). Furthermore, there is observational evidence that reconnection at a 3D null may be important in some solar flares 8 , as well as in eruptive phenomena in active regions 9 . In addition, the first in situ observation 10 of reconnection occurring at a 3D null point in the Earth's magnetotail has recently been made by the Cluster spacecraft. Moreover, current growth at 3D nulls has been observed in the laboratory 11 .The magnetic field topology and geometry in the vicinity of such a null can be described by the two sets of field lines which asymptotically approach, or recede from, the null. A pair of field lines approach (recede from) the null from opposite directions, defining the 'spine' (or γ-line) of the null. In addition, an infinite family of field lines recede from (approach) the null in a surface known as the fan (or Σ-) plane (see Refs. [2,12]).To this point, many studies of the MHD behaviour of 3D nulls have been kinematic, see e.g. Refs. [2,13,14,15]. However, a few solutions to the full set of MHD equations do exist for reconnection at current sheets located at 3D nulls, in incompressible plasmas. These incompressible solutions are based upon the technique first proposed by Craig & Henton 16 for the 2D reconnection problem. The solutions describe steady-state current sheets aligned...

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“…This equivalence highlights the inherent symmetry in the u and B disturbance fields. It is interesting that a similar reduction to Klein-Gordon form also occurs for ideal fan reconnection models (Craig & Fabling 1998;Tassi et al 2005). A key property in all cases is that unbounded exponential growth occurs if α 2 > β 2 .…”

Section: The Ideal Systemmentioning

confidence: 84%

“…3.2). More generally, we can determine inviscid solutions computationally -and assess the dynamic accessibility of the solution -by considering the time relaxation of the system (Tassi et al 2005). …”

Section: Time-relaxed Inviscid Solutionsmentioning

confidence: 99%

Viscous dissipation in 3D spine reconnection solutions

Craig

Lopez

2013

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Aims. We consider the influence of viscous dissipation on "spine" reconnection solutions in coronal plasmas. It is known from 2D and 3D "fan" reconnection studies that viscous losses can be important. We extend these arguments to 3D "spine" reconnection solutions. Methods. Steady 3D spine reconnection models were constructed by time relaxation of the governing visco-resistive MHD equations. Scaling laws were derived that compare the relative importance of viscous and resistive damping. Results. It is shown that viscous dissipation in spine reconnection models can dominate resistive damping by many orders of magnitude. A similar conclusion, but with less severe implications, applies to current sheet "fan" solutions. These findings are not sensitive to whether classical or Braginskii viscosity is employed.

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Dynamic accessibility of inflow and outflow reconnective solutions

Cited by 6 publications

References 29 publications

Three-dimensional null point reconnection regimes

Three-dimensional null point reconnection regimes

Current sheets at three-dimensional magnetic nulls: Effect of compressibility

Viscous dissipation in 3D spine reconnection solutions

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