【作者】 刘丽娟；

【导师】 汪毓明； M.Temmer；

【作者基本信息】 中国科学技术大学 ， 空间物理学， 2017， 博士

【摘要】 日冕物质抛射(CME)是太阳大气中最剧烈的爆发现象,也是灾害性空间天气的主要驱动源。其主要源区是太阳活动区(AR):超过60%CME产生自活动区。但是活动区的爆发能力也各不相同,有的活动区难以产生CME,有的能够在短时间内产生很多CME。什么样的活动区能够产生CME?为什么有的活动区能够频繁的产生CME?我们的工作试图回答这两个问题。针对第一个问题,我们将一个频繁产生耀斑但几乎没有CME爆发的活动区NOAA 12192同其他4个活动区进行了比较,其中两个活动区生产了很多耀斑和CME,另外两个活动区几乎没有产生CME。通过对比SDO/HMI的光球矢量磁场参数,我们发现三个能产生很多耀斑的活动区相对另外两个惰性活动区,有较大的磁通、电流和磁自由能,即它们的面积都比较大,都包含着强的电流系统以及磁自由能。因为充足的磁自由能是驱动耀斑的必要条件,因此这个结论是可以理解的,也和以往的研究相一致。进一步,我们发现将平均电流螺度,总的无符号电流螺度两个参数组合起来可以区分它们的CME爆发能力。产生了较多CME的活动区的平均电流螺度(|Hc|)较大,而只产生了很多耀斑的活动区NOAA 12192以及另外两个几乎没有爆发产生的活动区NOAA 11157和11428的数值很小。考虑无符号电流螺度(Hctotal),活动区NOAA 12192的数值同NOAA 11158、11429两个CME频发的活动区一样大,也就意味着活动区NOAA 12192中存在着手性相反、但对应总量相当的电流螺度。此外,通过分析爆发前的电流螺度分布情况我们发现:产生了很多CME的两个活动区的主爆发中性线两侧有强电流螺度集中,说明这两个活动区中存在磁绳;通过计算外推日冕磁场中的衰减因数发现:它们的日冕束缚场也衰减地较快,束缚较弱;与之对应的,没有爆发产生或者只产生耀斑的三个活动区中没有这种沿着中性线两侧集中分布的强电流螺度。研究结果表明,活动区是否产生CME与两个因素有关:(1)在爆发的位置要有作为CME前身结构的强剪切结构或者磁绳存在;(2)活动区上方的束缚较弱。针对第二个问题,我们首先研究了产生自第23太阳活动周的28个超级活动区的281个准同源CME(产生自同一个活动区的CME)的等待时间(CME及其之前的CME被日冕仪首次观测到的时间间隔)分布。我们发现该等待时间分布由两部分组成,两个分量在18小时处被隔开。第一部分是一个类高斯分布,其峰值在7小时左右,从统计的角度落在这个分量中的CME之间存在着物理关联。峰值等待时间有可能是准同源CME涉及的物理过程发展的时间尺度。我们在样本中加入了第24太阳活动周的两个超级活动区:NOAA 11158和11429,发现其等待时间依然呈现二分量分布,其中188个准同源CME的等待时间小于18小时,呈现类高斯分布,在7.5小时处达到峰值。我们进一步精确定位了 142个等待时间小于18小时的准同源CME的磁源区:定义同一条中性线的同一位置为同一个磁源区,而同一中性线的不同位置或者不同的中性线为不同磁源区;对于一个CME,如果它和它之前的CME产生自同一个磁源区,则该CME被定义为S型,产生自不同磁源区则被归类为D型。最终得到90个(63%)S-型准同源CME,和52个(37%)D型准同源CME。我们进一步在两种准同源CME中各选取了一个案例:S-型准同源CME及其之前的CME都产生于四极场NOAA 11158的一个偶极系统,D型准同源事件中的两个CME起源于ARNOAA 11429中两个不同的磁通量系统。通过对两个案例的详细分析,包括对衰减指数n,挤压因子Q以及螺绕数目Tw的研究,我们发现:在S型准同源CME中,其磁绳在爆发中经历了部分爆发过程:磁绳的一部分爆发为第一个CME,而另一部分存留下来并在稍后爆发形成第二个CME,这个过程可以看做自由能的多阶段释放过程;在整个爆发过程中,活动区一直通过剪切和通量浮现补充磁自由能,即磁自由能的持续补充可能是一系列S-型CME爆发的主要原因。在D型CME的爆发中,一条中性线上的一个磁绳部分爆发,形成了第一个CME,并影响了第二个CME的源区,使得其上方的双支磁绳的上支伴随着第一个CME 一起爆发。由于该上支磁绳同下支磁绳的手性相反,本来对下支磁绳施加向下的束缚力,在其爆发之后,这种束缚力消失,允许下支磁绳膨胀、上升,并通过重联获得更强的螺绕性,最终作为第二个CME的内核磁绳爆发出去,形成了第二个CME。这两类CME可能涉及到了不同的物理过程:S-型CME和它之前的CME处在磁自由能的重复释放过程中;D-型CME更可能是由其之前的CME扰动所引起的。其等待时间的不同峰值可能是这两类不同物理过程涉及到的特征时间。更多还原

【Abstract】 Coronal mass ejections(CMEs)are the major driving sources of hazardous space weather,while solar active regions(ARs)are the major sources of the CMEs.More than 60%CMEs originate from the ARs.So what are needed for an AR to produce CMEs,and how does a CME-rich AR produce CMEs successively?The thesis try to answer these questions.To answer the first one,we compared the recent super flare-rich but CME-poor AR 12192,with other four ARs;two were productive in both flares and CMEs and the other two were inert to produce any M-class or intenser flares or CMEs.By investigating the photospheric parameters based on the SDO/HMI vector magnetogram,we find the three productive ARs have larger magnetic flux,current and free magnetic energy than the inert ARs,which means that those ARs have larger sizes,and contain strong current system and free energy.Because enough magnetic free energy is a necessory condition for an AR to power a flare,thus,this conclusion is reasonable.Furthermore,we find that the combination of mean current helicity density and total unsigned current helicity can be used to distinguish the ARs’ CME productivity.ARs producing more CMEs have larger mean current helicity(|Hc|),but the ARs only producing flares or pro-ducing no eruptions has smaller mean current helicity.Considering the total unsigned current helicity(Hctotai),NOAA 12192 has as large value as the CME-productive AR,NOAA 11158 and 11429,which means ARNOAA 12192 contains current helicity with opposite handedness but equivalent amount.Furthermore,the two ARs productive in both flares and CMEs contain strong cur-rent helicity concentrating along both sides of the flaring neutral lines,indicating the presence of a seed flux rope;they also have higher decay index in the low corona,showing weak constraint.The results suggest that whether an AR is able to power a CME is seemingly related to(1)if there is significant twisted core field at the erupt-ing position serving as the seed of the CME flux rope and(2)if the constraint of the overlying arcades is weak enough.To answer the second question,we firstly do a statistical investigation of the wait-ing times(time difference between a CME and its proceeding one)of 281 quasi-homologous CMEs(i.e.,QH-CMEs,the CMEs successively originating from the same ARs)from 28 super ARs in solar cycle 23.The waiting time distribution consists of two compo-nents with a separation at about 18 hours.The first component looks like a Gaussian distribution and peaks at 7 hours.The peak waiting time probably characterize the time scale of the gradual release of the free energy or the growth of instabilities triggered by the preceding CMEs.The QH-CMEs in the first component are more likely to be phys-ically related.We further add two super ARs,NOAA 11158 and 11429 in solar cycle 24 into our sample,and analyze waiting time distribution of all the CMEs.We found that the distribution still consists of two component,in which 188 ones has waiting time less than 18 hours,showing a Gussian-like distribution with a peak at 7.5 hours.We define the same location of one PIL as the same magnetic source location,the different parts of one PIL or different PILs as different magnetic source locations,and further identified the precise magnetic source locations(i.e.,CME-related flux systems)of 142 QH-CMEs with waiting times less than 18 hours to check their possible mech-anisms.Among those CMEs,90 ones(63%)originate from the same location as their preceding ones,which are defined as S type CMEs;while 52(37%)ones originate from the different locations compared with their preceding ones,which are defined as D type CMEs.Waiting time distributions of the two types of QH CMEs have different peaks,7.5 hours for S-types while 1.5 hours for D-types.We furtherly selected two cases:the S-type QH CME and its predecessor are from the same bipolar system in AR NOAA 11158,the D type QH CME and its predessor originate from the different flux systems in AR NOAA 11429.Detailed analysis,in-cluding the decay index n,squashing factor Q and twist number Tw,of two CMEs of each type indicates:during the S-type eruption,the seed flux rope experienced a partial eruption process,part of the flux rope erupted,forming the first CME,the other part survived and erupted later;the whole process could be desribed as a multiple-stage energy release scenario,during which the free energy of the AR was refilled by contin-uous shear motion and flux emergence.During the D-type CME,a flux rope along one PIL erupted as the first CME,influenced the magnetic source of the second CME,made the upper flux rope along the second PIL erupted.The upper flux rope along the second PIL had the opposite handedness as the lower flux rope along the same PIL,exerting a downward force to the lower flux rope.After the eruption of the upper flux rope,the lower one lost its constraing force,started to expand,rise and finally erupted out as the second CME.In conclusion,the S type CME and its preceding one may experience a process of recurring release of free magnetic energy;the D type CME is more likely to be promoted by a sequence of disturbances caused by its preceding one.Different peaks of the two types of QH CMEs may represent the charasteristic time scales of the two physicla process.更多还原