Despite extensive research on various global waves in solar eruptions, debate continues on the intrinsic nature of them. In this work, we performed numerical experiments of the coronal mass ejection with emphases on the associated large-scale MHD waves. A fast-mode shock forms in front of the flux rope during the eruption with a dimming region following it, and the development of a three-component structure of the ejecta is observed. At the flank of the flux rope, the slow-mode shock and the velocity vortices are also invoked. The dependence of the eruption energetics on the strength of the background field and the coronal plasma density distribution is apparent: the stronger the background field is, and/or the lower the coronal plasma density is, the more energetic the eruption is. In the lower Alfve′n speed environment, the slow mode shock and the large scale velocity vortices may be the source of the EIT wave. In the high Alfve′n speed environment, on the other hand, the echo due to the reflection of the fast shock on the bottom boundary could be so strong that its interaction with the slow mode shock and the velocity vortices produces the second echo propagating downward and causing the secondary disturbance to the boundary surface. We suggest that this second echo, together with the slow shock and the velocity vortices, could constitute a possible candidate of the source for the EIT wave.
区域生长法是一种基于区域分割的算法,其关键在于种子点的准确提取和生长准则的定义。用区域生长法对云南天文台澄江1 m红外太阳塔望远镜(New Vacuum Solar Telescope,NVST)在TiO(705.8nm)波段的观测资料进行分析识别,采用拉普拉斯算子提取种子点,然后用图像灰度阈值作为生长准则对种子点进行生长,最后剔除误识别的米粒,从而完成对磁亮点的识别工作。然后又对Hinode的观测资料进行了识别并与Utz等人的结果进行对比。
During the total solar eclipse of July 22, 2009, we carried out a white-light observation in Anji, Zhejiang, China. The aim wasto observe the polar plumes (PPs) with high spatial and temporal resolutions in white-light. With the observational data, weinvestigate the properties and evolution of the PPs and compare them with those of the low-latitude plumes (LPs). We find thatboth the PPs and the LPs have comparable lengths and widths, and the mean length and width are 300 Mm and 16 Mm, re-spectively. The average inclination angle (13 degree) of the PPs is smaller than that (32 degree) of the LPs. Generally, theplumes which are closer to the coronal hole center are more vertical. We trace the PPs and the LPs in the sequence of imagesand find that none of them disappears and no new one is created. Additionally, neither plasma outflow nor transverse oscilla-tion is observed. These imply that the evolution process of plumes is much longer than the timescale of eclipse.
It is well known that some coronal jets exhibit helical structures and untwisting.We attempt to inspect the origin of twist in a blowout jet.By means of multiwavelength and multi-angle observations from Solar Dynamics Observatory (SDO) and Solar Terrestrial Relations Observatory-Ahead (STEREO-A),we firstly report a polar untwisting jet that is a blowout jet which leads to a jet-like coronal mass ejection.From the viewpoint of SDO,the jet shows clear untwisting behavior and two jet-spires.However,from the viewpoint of STEREO-A the jet actually comes from the whiplike prominence eruption and is followed by a white-light jet.Our observations indicate that twist in blowout jets may result from the erupting mini-prominences/minifilaments in the jet base.
Jun-Chao HongYun-Chun JiangJia-Yan YangRui-Sheng ZhengYi BiHai-Dong LiBo YangDan Yang
Using the multi-wavelength data from the Atmospheric Imaging Assembly (AIA)onboard the Solar Dynamics Observatory(SDO)spacecraft,we study a jet occurring in a coronal hole near the northern pole of the Sun.The jet presented distinct upward helical motion during ejection.By tracking six identified moving features (MFs)in the jet,we found that the plasma moved at an approximately constant speed along the jet's axis.Meanwhile,the MFs made a circular motion in the plane transverse to the axis.Inferred from linear and trigonometric fittings to the axial and transverse heights of the six tracks,the mean values of the axial velocities,transverse velocities,angular speeds,rotation periods,and rotation radii of the jet are 114 km s-1, 136 km s-1,0.81-s-1,452 s and 9.8×103 km respectively.As the MFs rose,the jet width at the corresponding height increased.For the first time,we derived the height variation of the longitudinal magnetic field strength in the jet from the assumption of magnetic flux conservation.Our results indicate that at heights of 1×104～7× 104 km from the base of the jet,the flux density in the jet decreases from about 15 to 3 G as a function of B=0.5(R/R⊙-1)-0.84(G).A comparison was made with other results in previous studies.
