3D Alfvén wave behaviour about proper and improper magnetic null points

Thurgood, Jonathan; McLaughlin, James

doi:10.1051/0004-6361/201322021

Cited by 14 publications

(17 citation statements)

References 46 publications

(63 reference statements)

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“…Recently, Thurgood & McLaughlin [39,40] have studied the behaviour of Alfvén waves (which travel at the Alfvén speed parallel to the field), in the vicinity of both two-and three-dimensional nulls. Their work suggests that these waves may become phase-mixed near null points, again causing heating.…”

Section: (A) Behaviour Of Wave Pulses At Topological Featuresmentioning

confidence: 99%

Is magnetic topology important for heating the solar atmosphere?

Parnell

Stevenson

Threlfall

et al. 2015

Phil. Trans. R. Soc. A.

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Magnetic fields permeate the entire solar atmosphere weaving an extremely complex pattern on both local and global scales. In order to understand the nature of this tangled web of magnetic fields, its magnetic skeleton, which forms the boundaries between topologically distinct flux domains, may be determined. The magnetic skeleton consists of null points, separatrix surfaces, spines and separators. The skeleton is often used to clearly visualize key elements of the magnetic configuration, but parts of the skeleton are also locations where currents and waves may collect and dissipate. In this review, the nature of the magnetic skeleton on both global and local scales, over solar cycle time scales, is explained. The behaviour of wave pulses in the vicinity of both nulls and separators is discussed and so too is the formation of current layers and reconnection at the same features. Each of these processes leads to heating of the solar atmosphere, but collectively do they provide enough heat, spread over a wide enough area, to explain the energy losses throughout the solar atmosphere? Here, we consider this question for the three different solar regions: active regions, open-field regions and the quiet Sun. We find that the heating of active regions and open-field regions is highly unlikely to be due to reconnection or wave dissipation at topological features, but it is possible that these may play a role in the heating of the quiet Sun. In active regions, the absence of a complex topology may play an important role in allowing large energies to build up and then, subsequently, be explosively released in the form of a solar flare. Additionally, knowledge of the intricate boundaries of open-field regions (which the magnetic skeleton provides) could be very important in determining the main acceleration mechanism(s) of the solar wind.

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Section: (A) Behaviour Of Wave Pulses At Topological Featuresmentioning

confidence: 99%

Is magnetic topology important for heating the solar atmosphere?

Parnell

Stevenson

Threlfall

et al. 2015

Phil. Trans. R. Soc. A.

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“…Such cylindrical current concentrations are thought to form in the vicinity of null points due to generic, externally originating MHD waves, which collect near nulls and assume the cylindrical profile of the Alfv en speed isosurfaces due to refraction. [27][28][29] Against the background field B 0 , this perturbation causes the separatrices of the field to be no longer perpendicular, but instead within r 1 assume the angle a ¼ cos À1 ðj 0 =2Þ. Outside of this region, they asymptotically tend towards their unperturbed positions.…”

Section: à2mentioning

confidence: 99%

Resistively-limited current sheet implosions in planar anti-parallel (1D) and null-point containing (2D) magnetic field geometries

2018

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Implosive formation of current sheets is a fundamental plasma process. Previous studies focused on the early time evolution, while here our primary aim is to explore the longer-term evolution, which may be critical for determining the efficiency of energy release. To address this problem we investigate two closely-related problems, namely: (i) 1D, pinched anti-parallel magnetic fields and (ii) 2D, null point containing fields which are locally imbalanced ('null-collapse' or 'X-point collapse'). Within the framework of resistive MHD, we simulate the full nonlinear evolution through three distinct phases: the initial implosion, its eventual halting mechanism, and subsequent evolution post-halting. In a parameter study, we find the scaling with resistivity of current sheet properties at the halting time is in good agreement -in both geometries -with that inferred from a known 1D similarity solution. We find that the halting of the implosions occurs rapidly after reaching the diffusion scale by sudden Ohmic heating of the dense plasma within the current sheet, which provides a pressure gradient sufficient to oppose further collapse and decelerate the converging flow. This back-pressure grows to exceed that required for force balance and so the post-implosion evolution is characterised by the consequences of the current sheet 'bouncing' outwards. These are: (i) the launching of propagating fast MHD waves (shocks) outwards and (ii) the width-wise expansion of the current sheet itself. The expansion is only observed to stall in the 2D case, where the pressurisation is relieved by outflow in the reconnection jets. In the 2D case, we quantify the maximum amount of current sheet expansion as it scales with resistivity, and analyse the structure of the reconnection region which forms post-expansion, replete with Petschek-type slow shocks and fast termination shocks.This accepted paper has been published open access in Physics of Plasmas, 25, 072105 (2018).

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“…It is still a mystery why the solar corona is so hot compared to the other layers of the atmosphere. There are many theories to explain coronal heating such as magnetic reconnection models and wave heating models (Priest & Forbes 2000;Heyvaerts & Priest 1983;Thurgood & McLaughlin 2013).…”

Section: Temperature Evolutionsmentioning

confidence: 99%

Plasmoids and Resulting Blobs due to the Interaction of Magnetoacoustic Waves with a 2.5D Magnetic Null Point

Sabri

Ebadi

Poedts

2020

ApJ

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We performed a numerical study for interpreting observations of plasma blobs occurring in the solar corona. Considering all of the previous studies and the presence of magnetic null points together with propagating MHD waves in the solar corona, we guessed that the interaction of fast magnetoacoustic waves with null points could give rise to blobs under coronal conditions. The outcome of these interactions contributes to coronal jets and flares which directly affects us on Earth. The propagation of magnetoacoustic waves in the vicinity of a magnetic null point contributes to the high current density accumulation at the small scale around the magnetic null point which has significant magnetic gradients. When nonlinearity gets dominant, the variation of current density could result in instabilities and thus anomalous resistivity. Moreover, it is demonstrated that plasmoids with eruption events take place in the solar corona without considering the transition region. In our numerical simulation results, it is interesting that plasma blobs manifest themselves in many parameters including current density, temperature, plasma density, flows and magnetic fields simultaneously, and consistent with the generation of plasmoids. In this work, it is found that plasmoid instability is the reason of the plasma blobs and tiny blobs are produced by the tearing instability occurring in thin current sheets.

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3D Alfvén wave behaviour about proper and improper magnetic null points

Cited by 14 publications

References 46 publications

Is magnetic topology important for heating the solar atmosphere?

Is magnetic topology important for heating the solar atmosphere?

Resistively-limited current sheet implosions in planar anti-parallel (1D) and null-point containing (2D) magnetic field geometries

Plasmoids and Resulting Blobs due to the Interaction of Magnetoacoustic Waves with a 2.5D Magnetic Null Point

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