LIGHT BRIDGE IN A DEVELOPING ACTIVE REGION. II. NUMERICAL SIMULATION OF FLUX EMERGENCE AND LIGHT BRIDGE FORMATION
LIGHT BRIDGE IN A DEVELOPING ACTIVE REGION. II. NUMERICAL SIMULATION OF FLUX EMERGENCE AND LIGHT BRIDGE FORMATION
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DOI：
10.1088/0004-637x/811/2/138
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发表时间：
2015-09
期刊：
影响因子：
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通讯作者：
S. Toriumi;M. Cheung;Y. Katsukawa
中科院分区：
文献类型：
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作者：
S. Toriumi;M. Cheung;Y. Katsukawa
光桥是划分黑子区本影的明亮结构，它显示了各种活动事件。在第一篇论文中，我们报道了在一个发展中的活动区（AR）的光桥的多波长观测的分析，并得出结论，活动事件是由磁对流演化驱动的磁重联引起的。第二篇论文的目的是研究详细的磁场和速度结构以及光桥的形成机制。为此，我们分析了一个新兴的AR的辐射磁流体动力学模型的数值模拟数据。我们发现，弱磁化的等离子体在对流区的近表面层的上升流夹带在新兴的磁束，出现在太阳表面的孔隙。这种对流上升流不断地将水平场输送到表层，并形成轻桥结构。由于桥的水平场与周围孔隙的垂直场之间的磁剪切，在桥上方形成细长的尖形电流层，这可能有利于磁重联。论文Ⅰ的观测结果与本文的数值计算结果之间的惊人的一致性提供了一个一致的光桥物理图象。动力活动现象的发生是桥的形成及其对流性质的自然结果，这与本影点和半影丝有许多共同之处。
Light bridges, the bright structure dividing umbrae in sunspot regions, show various activity events. In Paper I, we reported on an analysis of multi-wavelength observations of a light bridge in a developing active region (AR) and concluded that the activity events are caused by magnetic reconnection driven by magnetconvective evolution. The aim of this second paper is to investigate the detailed magnetic and velocity structures and the formation mechanism of light bridges. For this purpose, we analyze numerical simulation data from a radiative magnetohydrodynamics model of an emerging AR. We find that a weakly magnetized plasma upflow in the near-surface layers of the convection zone is entrained between the emerging magnetic bundles that appear as pores at the solar surface. This convective upflow continuously transports horizontal fields to the surface layer and creates a light bridge structure. Due to the magnetic shear between the horizontal fields of the bridge and the vertical fields of the ambient pores, an elongated cusp-shaped current layer is formed above the bridge, which may be favorable for magnetic reconnection. The striking correspondence between the observational results of Paper I and the numerical results of this paper provides a consistent physical picture of light bridges. The dynamic activity phenomena occur as a natural result of the bridge formation and its convective nature, which has much in common with those of umbral dots and penumbral filaments.