活动区日冕物质抛射的形成条件及产生规律

发布时间：2018-08-26 15:53

【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。
[Abstract]:Coronal mass ejection (CME) is the most violent eruption phenomenon in the solar atmosphere and the main driving force of disastrous space weather. Its main source area is the solar active region (AR): more than 60% of CME is generated from the active region. But the explosive capacity of the active region is also different, some of the active regions are difficult to produce CME, and some can produce a lot of CME in a short time. E. What kind of active areas can produce CME? Why can some active areas produce CME frequently? Our work attempts to answer these two questions. To answer the first question, we compared NOAA 12192, an active area with frequent flares but few CME outbreaks, with four other active areas, two of which were produced. Many flares and CMEs, and few CMEs are produced in the other two active regions. By comparing the parameters of the photospherical vector magnetic field of SDO/HMI, we find that the three active regions which can produce many flares have larger flux, current and magnetic free energy than the other two inert active regions, i.e. they have larger area and contain a strong current system. Because sufficient magnetic free energy is a necessary condition for driving flares, this conclusion is understandable and consistent with previous studies. Further, we find that the CME bursting ability of the flares can be distinguished by combining the average current helicity and the total unsigned current helicity. The average current helicity (| Hc |) in the active region is large, but the values of NOAA 12192 and the other two active regions NOAA 11157 and 11428, which only produce many flares, are small. Considering the unsigned current helicity (Hctotal), the values of NOAA 12192 in the active region are the same as those of NOAA 11158, 11429 CME. In addition, by analyzing the current helicity distribution before the outbreak, we find that there is a concentration of strong current helicity on both sides of the main neutral line of the two active areas of CME, indicating that there is a magnetic rope in the two active areas. The decay factor of extrapolated coronal magnetic field shows that their coronal binding field also decays faster and weaker, and correspondingly, there is no such strong current helicity along both sides of the neutral line in the three active regions where there is no explosion or only flare. For the second problem, we first studied the waiting time of 281 quasi-homologous CMEs (CMEs from the same active region) from 28 superactive regions of the 23rd solar cycle. The first part is a Gaussian-like distribution with a peak value of about 7 hours. Statistically, there is a physical correlation between the CMEs falling in this component. The peak waiting time may be a time scale for the development of physical processes involved in quasi-homologous CMEs. We add two super-active regions of solar cycle 24: NOAA 11158 and 11429 to the sample and find that the waiting time still presents a two-component distribution. Among them, 188 quasi-homologous CMEs have a waiting time of less than 18 hours, showing a Gaussian-like score. We further pinpointed 142 quasi-homologous CMEs with waiting times of less than 18 hours: defined the same position of the same neutral line as the same magnetic source area, and different positions or neutrals of the same neutral line as different magnetic source areas; for a CME, if it is before it Finally, 90 (63%) S-type quasi-homologous CMEs and 52 (37%) D-type quasi-homologous CMEs were obtained. We further selected one case in each of the two quasi-homologous CMEs: the S-type quasi-homologous CME and its predecessor CME were all produced in the quadrupole field NOAA. A dipole system in 11158, two CMEs in the D-type quasi-homologous event originate from two different magnetic flux systems in ARNOAA 11429. Through detailed analysis of two cases, including attenuation exponent n, extrusion factor Q and the number of coils Tw, we find that in the S-type quasi-homologous CME, the magnetic rope undergoes a partial explosion. PROCESS: One part of the magnetic rope explodes into the first CME, while the other part remains and then explodes to form the second CME. This process can be regarded as a multi-stage release process of free energy. The main cause of a series of S-type CME bursts. In the D-type CME bursts, a magnetic rope on a neutral line partially explodes, forming the first CME and affecting the source region of the second CME, causing the upper branch of the two magnetic ropes above to erupt with the first CME. Since the upper branch of the magnetic rope is chirally opposite to the lower branch, it is originally paired down. The downward binding force exerted by the supporting magnetic rope disappears after its explosion, allowing the lower magnetic rope to expand, rise, and obtain greater spiral coiling through reconnection. Finally, the core magnetic rope of the second CME explodes, forming a second CME. These two types of CMEs may involve different physical processes: the S-type CME and the CME before it. In the process of repeated release of magnetic free energy, the D-type CME is more likely to be caused by the CME perturbation before it. The different peak values of the waiting time may be the characteristic time involved in the two different physical processes.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P182.62

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