3D WKB solution for fast magnetoacoustic wave behaviour within a separatrix dome containing a coronal null point

McLaughlin, James; Thurgood, Jonathan; Botha, G. J. J.; Wiggs, Joshua A

doi:10.1093/mnras/stz085

Cited by 6 publications

(5 citation statements)

References 38 publications

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“…Next, we try to find the effect of the nonlinear perturbation on the temperature profile. In previous studies, it was shown that the propagation of the fast magnetoacoustic pulse around the null point results in the excitation of the current sheet around the null point (McLaughlin et al 2019;Sabri et al 2019. Moreover, it was illustrated that the magnetic null point collapsed to form a current sheet oscillating between ±∼45°.…”

Section: Numerical Results and Discussionmentioning

confidence: 96%

How Nonlinearity Changes Different Parameters in the Solar Corona

Sabri

Poedts

Ebadi

2023

ApJ

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We consider different velocity amplitudes of incident waves to study nonlinearity effects on the plasma parameters around a magnetic null point in the solar corona. This could query the seismological methods used to observe and interpret damping profiles of oscillations of magnetic structures, based on linear theory. To this end, initially symmetric fast magnetoacoustic waves with three different amplitudes are applied to the system to pursue the effect of nonlinearity on the resulting plasma heating and flows. The dynamic evolution is investigated by solving the resistive MHD equations in a Cartesian domain by the PLUTO code. The considered magnetic null point is surrounded by an initially constant density and temperature plasma. Pursuing the partition of different energy components can shed light on our understanding of the energy release mechanisms. It is found that nonlinear behavior could be the reason for the occurring magnetic reconnection and the related excitation of coronal jets. Furthermore, the fully nonlinear simulation run results in a high temperature and a high current density accumulation and less twisting along the wave accumulation direction, which is even higher than the heating at the magnetic null point itself. Moreover, it is found that there is no significant amplification in the velocity profile. This could be related to the fact that there are not any clear correlations between jets and flares. Furthermore, it is illustrated that the period of the oscillations depends on the amplitude of the initial perturbation, obtaining a shorter period for the fully nonlinear case.

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Section: Numerical Results and Discussionmentioning

confidence: 96%

How Nonlinearity Changes Different Parameters in the Solar Corona

Sabri

Poedts

Ebadi

2023

ApJ

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“…Another further step into the 3D realm has already been taken by McLaughlin et al (2019), who performed a 3D WKB study of fast wave refraction in a 3D dome topology. They could not address mode conversion due to their cold plasma approximation, by they did determine that the ability of a null to directly capture wave energy decreases as the null height increases above the photosphere.…”

Section: Discussionmentioning

confidence: 99%

The Formation and Dissipation of Current Sheets and Shocks due to Compressive Waves in a Stratified Atmosphere Containing a Magnetic Null

Tarr

Linton

2019

ApJ

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We study the propagation and dissipation of magnetohydrodynamic waves in a set of numerical models that each include a solar-like stratified atmosphere and a magnetic field with a null point. All simulations have the same magnetic field configuration but different transition region heights. Compressive wave packets introduced in the photospheric portion of the simulations refract towards the null and collapse it into a current sheet, which then undergoes reconnection. The collapsed null forms a current sheet due to a strong magnetic pressure gradient caused by the inability of magnetic perturbations to cross the null. Although the null current sheet undergoes multiple reconnection episodes due to repeated reflections off the lower boundary, we find no evidence of oscillatory reconnection arising from the dynamics of the null itself. Wave mode conversion around the null generates a series of slow mode shocks localized near each separatrix. The shock strength is asymmetric across each separatrix, and subsequent shock damping therefore creates a tangential discontinuity across each separatrix, with long-lived current densities. A parameter study of the injected wave energy to reach the null confirms our previous WKB estimates. Finally, using current estimates of the photospheric acoustic power, we estimate that the shock and Ohmic heating we describe may account for ≈ 1 − 10% of the radiative losses from coronal bright points with similar topologies, and are similarly insufficient to account for losses from larger structures such as ephemeral regions. At the same time, the dynamics are comparable to proposed mechanisms for generating type-II spicules.

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“…These new results have drawn renewed interest in wave-heating mechanisms, both observationally and theoretically. Combinations of MHD wave aspects, vortices, and null point ingredients have only been studied to a certain extent (McLaughlin et al 2011(McLaughlin et al , 2019Thurgood & McLaughlin 2013;Shelyag et al 2013;Mumford et al 2015;Tarr et al 2017;Tarr & Linton 2019;Liu et al 2019;Tziotziou et al 2020;Battaglia et al 2021). Because vortex flows, resulting torsional Alfvén waves, and localized null points are so common, their co-occurrence is quite likely, opening up new challenges in the study of wave and energy propagation.…”

Section: Introductionmentioning

confidence: 99%

3D MHD wave propagation near a coronal null point: New wave mode decomposition approach

Yadav

Keppens

Braileanu

2022

A&A

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Context. Ubiquitous vortex flows at the solar surface excite magnetohydrodynamic (MHD) waves that propagate to higher layers of the solar atmosphere. In the solar corona, these waves frequently encounter magnetic null points. The interaction of MHD waves with a coronal magnetic null in realistic 3D setups requires an appropriate wave identification method. Aims. We present a new MHD wave decomposition method that overcomes the limitations of existing wave identification methods. Our method allows for an investigation of the energy fluxes in different MHD modes at different locations of the solar atmosphere as waves generated by vortex flows travel through the solar atmosphere and pass near the magnetic null. Methods. We used the open-source MPI-AMRVAC code to simulate wave dynamics through a coronal null configuration. We applied a rotational wave driver at our bottom photospheric boundary to mimic vortex flows at the solar surface. To identify the wave energy fluxes associated with different MHD wave modes, we employed a wave decomposition method that is able to uniquely distinguish different MHD modes. Our proposed method utilizes the geometry of an individual magnetic field-line in the 3D space to separate the velocity perturbations associated with the three fundamental MHD waves. We compared our method with an existing wave decomposition method that uses magnetic flux surfaces instead. Over the selected flux surfaces, we calculated and analyzed the temporally averaged wave energy fluxes, as well as the acoustic and magnetic energy fluxes. Our wave decomposition method allowed us to estimate the relative strengths of individual MHD wave energy fluxes. Results. Our method for wave identification is consistent with previous flux-surface-based methods and provides the expected results in terms of the wave energy fluxes at various locations of the null configuration. We show that ubiquitous vortex flows excite MHD waves that contribute significantly to the Poynting flux in the solar corona. Alfvén wave energy flux accumulates on the fan surface and fast wave energy flux accumulates near the null point. There is a strong current density buildup at the spine and fan surface. Conclusions. The proposed method has advantages over previously utilized wave decomposition methods, since it may be employed in realistic simulations or magnetic extrapolations, as well as in real solar observations whenever the 3D fieldline shape is known. The essential characteristics of MHD wave propagation near a null – such as wave energy flux accumulation and current buildup at specific locations – translate to the more realistic setup presented here. The enhancement in energy flux associated with magneto-acoustic waves near nulls may have important implications in the formation of jets and impulsive plasma flows.

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3D WKB solution for fast magnetoacoustic wave behaviour within a separatrix dome containing a coronal null point

Cited by 6 publications

References 38 publications

How Nonlinearity Changes Different Parameters in the Solar Corona

How Nonlinearity Changes Different Parameters in the Solar Corona

The Formation and Dissipation of Current Sheets and Shocks due to Compressive Waves in a Stratified Atmosphere Containing a Magnetic Null

3D MHD wave propagation near a coronal null point: New wave mode decomposition approach

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