Linear and nonlinear MHD mode coupling of the fast magnetoacoustic wave about a 3D magnetic null point
Linear and nonlinear MHD mode coupling of the fast magnetoacoustic wave about a 3D magnetic null point
复制标题
3D 磁零点附近快速磁声波的线性和非线性 MHD 模式耦合
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
James McLaughlin
中科院分区：
文献类型：
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作者：
J. Thurgood;James McLaughlin
内容：
在二维模型中，日冕磁零点被认为是局部加热事件的可能位置。我们调查这种可能性完全三维零点。
目的：
我们调查的性质的快速磁声波关于一个完整的三维磁零点，在其传播的具体利益，我们寻找证据的MHD模式耦合和/或转换到阿尔芬模式。
研究方法：
构造了一种特殊的场线和磁通坐标系，允许在适当和不适当的三维零点附近引入纯快磁声波。本文考虑了理想β = 0的MHD方程，用LARE 3D数值程序求解。利用特殊坐标系，分离并识别了合成波的各组成模式
系统数值结果得到了支持的分析工作来自微扰理论和线性实施的WKB方法。
结果如下：
一个最初的纯快波被发现是永久解耦的Alfven模式线性和非线性的适当和不适当的三维零点。纯快模式还产生并维持沿平衡磁场沿着排列的非线性扰动。由此产生的纯快速磁声脉冲具有瞬态行为，这被发现是由（平衡）阿尔芬速度分布，和折射效应集中所有的波能量朝向零点。
结论：
因此，从以前的2D工作的主要结果确实结转到全3D磁零点，所以我们得出结论，3D零点是由3D快磁声波在日冕中优先加热的位置
Context:
Coronal magnetic null points have been implicated as possible locations for localised heating events in 2D models. We investigate this possibility about fully 3D null points.
Aims:
We investigate the nature of the fast magnetoacoustic wave about a fully 3D magnetic null point, with a specific interest in its propagation, and we look for evidence of MHD mode coupling and/or conversion to the Alfven mode.
Methods:
A special fieldline and flux-based coordinate system was constructed to permit the introduction of a pure fast magnetoacoustic wave in the vicinity of proper and improper 3D null points. We considered the ideal, β = 0, MHD equations, which are solved using the LARE3D numerical code. The constituent modes of the resulting wave were isolated and identified using the special coordinate
system. Numerical results were supported by analytical work derived from perturbation theory and a linear implementation of the WKB method.
Results:
An initially pure fast wave is found to be permanently decoupled from the Alfven mode both linearly and nonlinearly for both proper and improper 3D null points. The pure fast mode also generates and sustains a nonlinear disturbance aligned along the equilibrium magnetic field. The resulting pure fast magnetoacoustic pulse has transient behaviour, which is found to be governed by the (equilibrium) Alfven-speed profile, and a refraction effect focuses all the wave energy towards the null point.
Conclusions:
Thus, the main results from previous 2D work do indeed carry over to the fully 3D magnetic null points and so we conclude that 3D null points are locations for preferential heating in the corona by 3D fast magnetoacoustic waves