太阳爆发日珥内双向喷流事件的紫外光谱研究（英文）

SOHO/SUMER Observations of Transition Region Explosive Events in Prominence

太阳双向喷流事件是过渡区重要的小尺度现象之一。双向喷流事件的光谱特征是强的展宽和非高斯形状。当双向喷流事件发生时,光谱像的红、蓝两翼分别或者同时明显增强,其相应的多普勒速度可达100 km·s^(-1)以上。双向喷流事件的平均尺度约1 800 km,寿命约60 s。双向喷流事件出现在磁对消区附近,且其速度与当地的阿尔芬速度相当,普遍认为其产生机制为小尺度快速磁重联。对其系统、全面地研究始于SOHO时代。SOHO/SUMER具有高时空和谱分辨率、宽的谱线覆盖,其观测的光谱数据为探究双向喷流事件提供了有力的光谱学诊断工具。双向喷流事件及其他过渡区小尺度现象的相互联系已被广泛研究,但双向喷流事件与日珥及其精细结构的关系研究还很少。文章通过SOHO/SUMER的SiⅢ谱线的定点观测,再现了爆发日珥演化的强度、多普勒速度和宽度演化图。通过SiⅢ谱线分析,找出宽度大于三个标准偏差的SiⅢ谱线,然后进行视像筛选出双向喷流事件,最终在爆发日珥中诊断出多个双向喷流事件,且大多数的双向喷流事件以准周期20 min重复出现在爆发日珥的中心区域。通过讨论,认为日珥中心磁流管之间的磁重联导致了双向喷流事件的重复出现,双向喷流事件产生的高速等离子体流可能是日面物质抛射的一部分,或是跟随日面物质抛射的太阳风的一部分。

Explosive events（EEs） are small-scale dynamic phenomena often observed in the solar transition region（TR）.EEs are characterized by non-Gaussian and broad profiles with enhancements in the blue/red wings with an average line-of-sight Doppler velocities of ～100 km · s^-1.They have a small spatial scale of about1 800 km and a short lifetime of about 60 s on average.EEs are often found to be associated with magnetic cancellation and reveal bi-directional flows with high velocities comparable to the local Alfven velocity;they are generally regarded as the consequence of small-scale fast magnetic reconnections.Since the launch of SOHO spacecraft,the SUMER（solar ultraviolet measurements of emitted radiation） spectrograph has been widely used to study EEs.With high spatial and spectral resolution,and wide spectral coverage,SUMER was a powerful tool of ultraviolet spectroscopy and it has greatly increased our knowledge of EEs.Relationship between EEs and other small-scale events observed in the transition region,such as blinkers and EUV spicules have also been investigated during the SOHO era.However,the association between EEs and large-scale events such as prominence remains unclear.A sit-and-stare mode observation made by SUMER is selected for the study.We investigate the properties of EEs in a prominence.EEs are identified with analysis of the width of Si Ⅲ line（111.3 nm）.The Si Ⅲ lines with a width greater than three standard deviations（3σ） were singled out for further visual inspection to finally determine the occurrence of EEs.It is found that the vast majority of explosive events concentrate in the bright knots of the prominence.EEs in the core of the prominence occur repetitively with a period of about 20 mins.It is proposed that the explosive events caused by small-scale fast magnetic reconnections are triggered by magnetic flux loops in the core of prominence.The blue shift of the explosive events is significant and possibly related to the initiation of a CME.