NONLINEAR THREE-DIMENSIONAL MAGNETOCONVECTION AROUND MAGNETIC FLUX TUBES
NONLINEAR THREE-DIMENSIONAL MAGNETOCONVECTION AROUND MAGNETIC FLUX TUBES
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DOI：
10.1088/0004-637x/731/2/108
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发表时间：
2011-04
期刊：
影响因子：
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通讯作者：
G. Botha;A. Rucklidge;N. Hurlburt
中科院分区：
文献类型：
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作者：
G. Botha;A. Rucklidge;N. Hurlburt
太阳光球层中的磁通量形成从小尺度（例如通量元素）到大尺度（例如太阳黑子）的浓度。本文介绍了超颗粒尺度上大型磁通量管（例如太阳黑子）的衰变过程的研究。三维非线性电阻磁流体动力学数值模拟在圆柱域中进行，用轴对称解初始化，该解由明确定义的中心通量管和围绕它的环形对流单元组成。随着非线性对流的发展，环形单元在方位角方向上分裂成许多单元，使得磁通量在单元之间滑离中心通量管（湍流侵蚀）。这降低了中心管中的磁压，并且管内的对流增强，可能变得足够强以将管推开。中心通量管的残余物持续存在由其周围的对流引起的非对称扰动。远离中心管的对流单元之间形成二次通量集中。管的衰减取决于管周围的对流。随着时间相关的流出，管内形成的对流单元将消除磁通量。 （这对于小管来说最为明显。）当周围对流中捕获的通量被推向管时，通量就会添加到管中。当管内的对流被剩余磁场充分抑制时，管就会持续存在。所有持久管的例子都具有相同的有效磁场强度，这与孔隙和太阳黑子本影都具有大致相同的磁场强度的观察结果一致。
Magnetic flux in the solar photosphere forms concentrations from small scales, such as flux elements, to large scales, such as sunspots. This paper presents a study of the decay process of large magnetic flux tubes, such as sunspots, on a supergranular scale. Three-dimensional nonlinear resistive magnetohydrodynamic numerical simulations are performed in a cylindrical domain, initialized with axisymmetric solutions that consist of a well-defined central flux tube and an annular convection cell surrounding it. As the nonlinear convection evolves, the annular cell breaks up into many cells in the azimuthal direction, allowing magnetic flux to slip between cells away from the central flux tube (turbulent erosion). This lowers magnetic pressure in the central tube, and convection grows inside the tube, possibly becoming strong enough to push the tube apart. A remnant of the central flux tube persists with nonsymmetric perturbations caused by the convection surrounding it. Secondary flux concentrations form between convection cells away from the central tube. Tube decay is dependent on the convection around the tube. Convection cells forming inside the tube as time-dependent outflows will remove magnetic flux. (This is most pronounced for small tubes.) Flux is added to the tube when flux caught in the surrounding convection is pushed toward it. The tube persists when convection inside the tube is sufficiently suppressed by the remaining magnetic field. All examples of persistent tubes have the same effective magnetic field strength, consistent with the observation that pores and sunspot umbrae all have roughly the same magnetic field strength.