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arXiv 0705.2507astro-ph
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太阳黑子周围移动磁特征对的速度结构:对U环模型的支持

The velocity structure of moving magnetic feature pairs around sunspots: support for the U-loop model

Jun Zhang, S. K. Solanki, J. Woch, Jingxiu Wang

摘要:

利用太阳和日光层天文台(SOHO)的迈克尔逊多普勒成像仪(MDI)记录的资料,追踪了NOAA ARs 8375、0330和9575三个活动区的123对相反磁极性的移动磁特征(MMFs)。在观察时,AR 8375是年轻的,AR 0330成熟,AR 9575腐烂。垂直速度表明,与黑子极性相反的MMF对的元素支持约50-100米秒$^{-1}$的下降流。在AR 8375中,MMF对的负元素和正元素之间的平均多普勒频移差约为150 m s $^{-1}$,在AR 0330中约为100 m s $^{-1}$,在AR 9575中约为20 m s $^{-1}$。这些观测结果与模型一致,即MMF对是从太阳黑子的磁冠发出的U环的一部分。根据这个模型,下降流是由埃弗谢德流返回太阳表面以下引起的。对于AR 8375,MMF的水平速度范围从0.1 km s $^{-1}$到0.7 km s $^{-1}$,平均而言,随着距离MMF诞生地的距离增加,MMF对的速度显著降低(从0.6 km s $^{-1}$到0.35 km s $^{-1}$)。这一结果表明,在MMF流速的变化并不反映护城河流的径向结构,而是内在的MMF对的演变。这一结果也与磁动势对的U环模型一致。我们还发现,MMF对的属性,最引人注目的寿命,取决于父黑子的演化阶段。AR 9575和0330中MMF对的平均寿命分别为0.7小时和1.6小时,这大大短于先前发现的AR 8375的4小时寿命。

英文摘要:

Using data recorded by the Michelson Doppler Imager (MDI) instrument on the Solar and Heliospheric Observatory (SOHO), we have traced 123 pairs of opposite magnetic polarity moving magnetic features (MMFs) in three active regions NOAA ARs 8375, 0330 and 9575. At the time of observation, AR 8375 was young, AR 0330 mature, and AR 9575 decaying. The vertical velocity indicates that the elements of MMF pairs with polarity opposite to that of the sunspot support a downflow of around 50-100 m s$^{-1}$. The average Doppler shift difference between negative and positive elements of an MMF pair is about 150 m s$^{-1}$ in AR 8375, 100 m s$^{-1}$ in AR 0330, and 20 m s$^{-1}$ in AR 9575. These observational results are in agreement with the model that MMF pairs are part of a U-loop emanating from the sunspot's magnetic canopy. According to this model the downflow is caused by the Evershed flow returning below the solar surface. For AR 8375, the horizontal velocity of MMFs ranges from 0.1 km s$^{-1}$ to 0.7 km s$^{-1}$, and on average, the velocity of an MMF pair decreases significantly (from 0.6 km s$^{-1}$ to 0.35 km s$^{-1}$) with increasing distance from the MMF's birth place. This result suggests that the change in MMF flow speed does not reflect the radial structure of the moat flow, but rather is intrinsic to the evolution of the MMF pairs. This result is also in agreement with the U-loop model of MMF pairs. We also find that properties of MMF pairs, most strikingly the lifetime, depend on the evolution stages of the parent sunspot. The mean lifetimes of MMF pairs in ARs 9575 and 0330 are 0.7 hours and 1.6 hours, respectively, which is considerably shorter than the 4 hours lifetime previously found for AR 8375.

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