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arXiv 1209.4378astro-ph.SR
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用SDO/HMI观测太阳活动区的裸露出现

The naked emergence of solar active regions observed with SDO/HMI

Rebecca Centeno

摘要:

我们利用HMI/SDO仪器研究了太阳表面磁场第一个印记中活动区的裸露出现。为此,我们跟踪了两个相当孤立的AR生命的前24小时,它们在即将穿越中央子午线时出现在表面上。我们分析了多普勒速度和矢量磁场方向之间的相关性,一致地发现,连接主极性的水平场被相对较强的上升流拖到表面,并与细长的颗粒相关联,平均而言,比周围环境更亮。另一方面,主要的磁足点由垂直场和向下流动的等离子体主导。一旦AR达到一定大小,在主要足迹之间出现移动偶极特征(MDF)(与AR的极性相反)是相当常见的现象。能量场的浮力不足以将整个磁拱升起。取而代之的是,由于它所携带的等离子体的重量,场被固定在光球层的几个主要支点之间的地方,给了MDF生命,并使下行的等离子体通道成为可能。两极倾向于彼此漂移,合并和消失。这可能是下降场线中重连过程的特征,这减轻了一些重量,允许磁弧最终上升到HMI谱线的检测层之外。

英文摘要:

We take advantage of the HMI/SDO instrument to study the naked emergence of active regions from the first imprints of the magnetic field on the solar surface. To this end, we followed the first 24 hours in the life of two rather isolated ARs that appeared on the surface when they were about to cross the central meridian. We analyze the correlations between Doppler velocities and the orientation of the vector magnetic field finding, consistently, that the horizontal fields connecting the main polarities are dragged to the surface by relatively-strong upflows and are associated to elongated granulation that is, on average, brighter than its surroundings. The main magnetic footpoints, on the other hand, are dominated by vertical fields and downflowing plasma. The appearance of moving dipolar features, MDFs, (of opposite polarity to that of the AR) in between the main footpoints, is a rather common occurrence once the AR reaches a certain size. The buoyancy of the fields is insufficient to lift up the magnetic arcade as a whole. Instead, weighted by the plasma that it carries, the field is pinned down to the photosphere at several places in between the main footpoints, giving life to the MDFs and enabling channels of downflowing plasma. MDF poles tend to drift towards each other, merge and disappear. This is likely to be the signature of a reconnection process in the dipped field lines, which relieves some of the weight allowing the magnetic arcade to finally rise beyond the detection layer of the HMI spectral line.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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