Nonlinear Alfvén wave dynamics at a 2D magnetic null point: ponderomotive force

Thurgood, Jonathan; McLaughlin, James

doi:10.1051/0004-6361/201321338

Cited by 13 publications

(23 citation statements)

References 32 publications

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“…This was previously reported for Alfvén waves at 2D nulls (Thurgood & McLaughlin 2013b). There are two possible explanations:…”

Section: Proper Null =supporting

confidence: 78%

“…Nonlinearly, we also find that the theory of Alfvén waves at 2D magnetic null points (Thurgood & McLaughlin 2013b) carries over to the 3D case. Namely, in the manifestation of the daughter disturbances and the excitation of fast waves only during the driving phase.…”

Section: Resultsmentioning

confidence: 54%

“…4.2 of Thurgood & McLaughlin (2013b) for a comprehensive discussion of possible explanations outlined above. Finally, we do not clearly observe any cospatial disturbances manifest inĈ (transverse daughter disturbances).…”

Section: Proper Null =mentioning

confidence: 99%

“…ponderomotive force see, e.g., Nakariakov et al 1997;Verwichte et al 1999;Botha et al 2000;Tsiklauri et al 2001;Thurgood & McLaughlin 2013a). Thurgood & McLaughlin (2013b) found that at 2D nulls such mode excitation only occurred during driving at boundaries, and subsequently no further excitation occurred despite the inhomogeneous field. Overall, they determined that the effect did not significantly impact upon the dynamics of the main Alfvén wave.…”

Section: Introductionmentioning

confidence: 99%

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

Thurgood¹,

McLaughlin²

2013

A&A

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Context. Magnetohydrodynamic (MHD) waves and magnetic null points are both prevalent in many astrophysical plasmas, including the solar atmosphere. Interaction between waves and null points has been implicated as a possible mechanism for localised heating events. Aims. Here we investigate the transient behaviour of the Alfvén wave about fully 3D proper and improper magnetic null points. Methods. We introduce an Alfvén wave into the vicinity of both proper and improper null points by numerically solving the ideal, β = 0 MHD equations using the LARE3D code. A magnetic fieldline and flux-based coordinate system permits the isolation of resulting wave modes and the analysis of their interaction. Results. We find that the Alfvén wave propagates throughout the region and accumulates near the fan-plane, causing current build up. For different values of null point eccentricity, the qualitative behaviour changes only by the imposition of anisotropic pulse dilation, owing to the differing rates at which fieldlines diverge from the spine. For all eccentricities, we find that the fast and Alfvén waves are linearly decoupled. During the driving phase, an independently propagating fast wave is nonlinearly generated owing to the ponderomotive force. Subsequently, no further excitation of fast waves occurs. Conclusions. We find that the key aspects of the theory of Alfvén waves about 2D null points extends intuitively to the fully 3D case; i.e. the wave propagates along fieldlines and thus accumulates at predictable parts of the topology. We also highlight that unlike in the 2D case, in 3D Alfvén-wave pulses are always toroidal, and thus any aspects of 2D Alfvén-wave-null models that are pulse-geometry specific must be reconsidered in 3D.

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“…This was previously reported for Alfvén waves at 2D nulls (Thurgood & McLaughlin 2013b). There are two possible explanations:…”

Section: Proper Null =supporting

confidence: 78%

Section: Resultsmentioning

confidence: 54%

Section: Proper Null =mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Thurgood¹,

McLaughlin²

2013

A&A

Self Cite

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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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