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arXiv 1209.5286astro-ph.SRphysics.space-ph
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在日冕中用HINODE/EIS观测到的持续多普勒频移振荡:阿尔文波和循环上升流的光谱特征

Persistent Doppler shift oscillations observed with HINODE/EIS in the solar corona: spectroscopic signatures of Alfvenic waves and recurring upflows

Hui Tian, Scott W. McIntosh, Tongjiang Wang, Leon Ofman, Bart De Pontieu, Davina E. Innes, Hardi Peter

摘要:

利用太阳日冕仪上的极紫外成像光谱仪(EIS)获得的数据,我们对日冕中明显的、持续的(无明显阻尼的)多普勒频移振荡进行了观测。2007年2月至4月,我们主要发现了两种类型的振荡。一种是在循环足点区域发现的,主要周期约为10分钟。它们的特征是所有谱线参数(谱线强度、多普勒频移、谱线宽度和谱线不对称性)的相干行为、表观的蓝移和几乎贯穿整个持续时间的向蓝不对称性。这种振荡很可能是准周期性上升流(小尺度喷流或II型针状体的日冕对应物)的特征,这可能在向热日冕提供质量和能量方面发挥重要作用。另一种类型的振荡通常与回路的上部有关。它们在日冕线的多普勒频移中看得最清楚,形成温度在100万到200万度之间。这些振荡的全球子波通常在3-6分钟范围内的周期附近急剧达到峰值。没有发现明显的轮廓不对称性,并且线宽的变化通常非常小。强度变化通常小于2%。这些振荡更可能是扭结/阿尔芬波的签名,而不是流动。在少数情况下,在强度和多普勒频移振荡之间似乎存在π/2相移,这可能表明根据波动理论存在慢模式驻波。然而,我们证明,这样的相移也可以产生的循环移动到一个空间像素的阿尔文振荡的结果。在这种情况下,与阿尔文波相关的强度振荡是由环位移而不是密度变化引起的。

英文摘要:

Using data obtained by the EUV Imaging Spectrometer (EIS) onboard Hinode, we have per- formed a survey of obvious and persistent (without significant damping) Doppler shift oscillations in the corona. We have found mainly two types of oscillations from February to April in 2007. One type is found at loop footpoint regions, with a dominant period around 10 minutes. They are characterized by coherent behavior of all line parameters (line intensity, Doppler shift, line width and profile asymmetry), apparent blue shift and blueward asymmetry throughout almost the en- tire duration. Such oscillations are likely to be signatures of quasi-periodic upflows (small-scale jets, or coronal counterpart of type-II spicules), which may play an important role in the supply of mass and energy to the hot corona. The other type of oscillation is usually associated with the upper part of loops. They are most clearly seen in the Doppler shift of coronal lines with forma- tion temperatures between one and two million degrees. The global wavelets of these oscillations usually peak sharply around a period in the range of 3-6 minutes. No obvious profile asymmetry is found and the variation of the line width is typically very small. The intensity variation is often less than 2%. These oscillations are more likely to be signatures of kink/Alfven waves rather than flows. In a few cases there seems to be a pi/2 phase shift between the intensity and Doppler shift oscillations, which may suggest the presence of slow mode standing waves according to wave theories. However, we demonstrate that such a phase shift could also be produced by loops moving into and out of a spatial pixel as a result of Alfvenic oscillations. In this scenario, the intensity oscillations associated with Alfvenic waves are caused by loop displacement rather than density change.

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