光球涡管表面动力学过程分析的新方法
New approach for analysing dynamical processes on the surface of photospheric vortex tubes
摘要：
大多数关于多尺度涡旋运动的研究采用二维几何学，使用各种观测和数值资料。这种方法限制了对涡旋动力学物理过程本质的理解。在这里，我们开发了一种新的方法来从涡流管的边界面提取重要信息。利用三维高分辨率磁对流MURaM数值资料分析了光球粒间速度涡。基于流体元素的平流，采用拉格朗日平均涡度偏差（LAVD）技术确定涡结构的中心及其边界面。这些表面被映射到一个构造的包络网格，允许研究的关键等离子体参数的空间和时间的函数。有助于理解等离子体动力学的参数，例如洛伦兹力、压力、等离子体- $β$也被确定。我们的研究结果表明，虽然密度和压力具有相当全球性的行为，但其他物理量会发生局部变化，其大小和方向在空间和时间中发生变化。在表面处，水平方向上的混合效率不高，导致出现具有较高/较低温度的局部区域。此外，分析的MHD坡印廷通量证实，大部分的能量是在水平方向上。我们的研究结果还表明，压力和磁力，驱动等离子体的动态涡旋表面是不平衡的，因此，旋涡不旋转作为一个刚体。
英文摘要：
The majority of studies on multi-scale vortex motions employ a two-dimensional geometry by using a variety of observational and numerical data. This approach limits the understanding the nature of physical processes responsible for vortex dynamics. Here we develop a new methodology to extract essential information from the boundary surface of vortex tubes. 3D high-resolution magnetoconvection MURaM numerical data has been used to analyse photospheric intergranular velocity vortices. The Lagrangian Averaged Vorticity Deviation (LAVD) technique was applied to define the centers of vortex structures and their boundary surfaces based on the advection of fluid elements. These surfaces were mapped onto a constructed envelope grid that allows the study of the key plasma parameters as functions of space and time. Quantities that help in understanding the dynamics of the plasma, e.g. Lorentz force, pressure force, plasma-$β$ were also determined. Our results suggest that, while density and pressure have a rather global behaviour, the other physical quantities undergo local changes, with their magnitude and orientation changing in space and time. At the surface, the mixing in the horizontal direction is not efficient, leading to appearance of localized regions with higher/colder temperatures. In addition, the analysis of the MHD Poynting flux confirms that the majority of the energy is directed in the horizontal direction. Our findings also indicate that the pressure and magnetic forces that drive the dynamics of the plasma on vortex surfaces are unbalanced and therefore the vortices do not rotate as a rigid body.
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