【作者】 丁留贯；

【导师】 蒋勇； 李刚；

【作者基本信息】 南京信息工程大学 ， 空间天气学， 2013， 博士

【摘要】 太阳高能粒子(Solar Energetic Particle, SEP)事件与日冕物质抛射(Coronal Mass Ejection, CME)之间的关系是空间天气研究领域的一个重要内容,这一问题的解决有助于建立基于CME爆发的SEP预报模式以及提高现有预报模式的准确率。本文将"twin-CME"模型引入到SEP事件的研究中,采用典型事例分析和统计分析方法,给出由同一活动区相继爆发的"twin-CME"(主CME和先行CME)触发SEP事件的观测依据,并统计分析SEP事件与"twin-CME"爆发之间的关联,给出"twin-CME"比单个快速CME更利于触发SEP事件的依据。本文主要研究内容如下：首先,本文利用SOHO/LASCO、STEREO/SECCHI的CME观测结合磁通量管模型(Gradual Cylindral Shell,GCS)分析第24太阳活动周以来的强度较大的两个SEP事件和GLE事件的典型事例,发现这两个事例都能找到来自同一活动区的"twin-CME"爆发,且这两个CME的传播区域之间有一定程度的重叠。文中结合Ⅱ型射电暴、SDO/AIA图像、SDO/HMI磁图及非线性无力场外推(NLFFF)等综合分析了某些CME的爆发过程,进一步确定这些观测到的"twin-CME"为两个独立的CME构成而不是单个快速CME ("single-CME")爆发过程中不同阶段的两个形态。本文给出了触发SEP事件的对应"twin-CME"爆发的观测依据。其次,在个例分析的基础上,本文对第23太阳活动周的源区在日面西半球的126个快速CME和59个大型SEP事件进行统计分析,结果显示由"twin-CME"爆发产生的SEP事件的通量峰值与对应关联CME的速度、伴随耀斑的等级和1天前的低能粒子水平等三个参数之间无明显的相关性,而由单个快速CME爆发产生的SEP事件的通量峰值与这三个参数之间呈现明显的正相关。这一结论说明如果快速CME(主CME)之前有先行CME爆发,则主CME不一定需要很快的速度和很强的耀斑伴随,也不需要提前有很高的种子粒子水平,就可能产生很强的SEP事件。本文统计结果显示"twin-CME"会比单个快速CME更容易产生SEP事件(61%VS29%)。最后,本文讨论了与SEP事件相关的几个问题：一、通过分析先行CME选择标准中的时间间隔变化对"twin-CME"类SEP事件在SEP事件总数中的比例、单个快速CME不产生SEP事件的比例等的影响,本文给出了判断先行CME的时间阈值参考值,约12小时。二、估算高能粒子(>10MeV)的起始逃逸高度大约在15个太阳半径以下高度。相比单个CME而言,"twin-CME"可以在这一高度范围内产生更有效的粒子加速过程。因为先行CME产生的强烈扰动可以将预加速的日冕物质或耀斑物质长时间保持在这-高度,为激波加速提供需要的种子粒子。三、Ⅱ型射电暴的分析表明,在有无SEP两种情况下,Ⅱ射电暴爆发时的CME高度分布无明显的区别；统计结果显示有SEP事件发生的CME中Ⅱ型射电暴伴随比例较大。四、分析SEP事件时间通量廓线的变化快慢与源区相对磁足点的经度变化关系,结果显示相对磁足点东边的源区爆发的SEP事件的通量增长时间较长,而其增长速度相对较慢,即源区越在磁足点东边,其可能产生的SEP事件的通量峰值也就越小。这与较大强度的SEP事件通常发生在日面西半球的观测事实是一致的。综上所述,本文从观测角度研究SEP和CME的因果关联,结果表明由同一源区相继爆发的"twin-CME"比单个快速CME更易产生大SEP事件,文中给出了触发SEP事件的"twin-CME"爆发的观测依据。分析亦表明,在"twin-CME"产生的SEP事件中,快速CME的速度、伴随耀斑的强度等因素对SEP事件的强度决定作用较弱。本文给出了识别先行CME的时间阈值参考值为12小时。更多还原

【Abstract】 The relationsip between Solar Energetic Particle (SEP) events and Coronal Mass Ejection (CME) is an important problem in space weather study. The answer of this question is of help to establishing the prediction model of SEP events according to CME eruption and/or improving the accuracy of current SEP prediction model. This dissertation extanded the "twin CME" model to large SEP events, and used comprehensive analyses of representive SEP events and statistics of a large number of events, to present some observable evidances of the large SEP events triggered by "twin-CME" erupting from the same source region. We also analyzed the relationship between large SEP events and "twin-CME" eruptions, and gave some evidances of more effective particle acceleration process of the "twin-CME" than the "single-CME". The contents of this dissertation are summarized as the following:First, this dissertation analyzed extreme large SEP event and the first Ground Level Enhancement events (GLE) in Solar Cycle24with the help of Gradual Cylindral Shell (GCS) model, using CME observations by coronagraph instruments on board SOHO(LASCO) and Stereo-A/B(SECCHI) spacecrafts. The results showed that "twin-CME" erupting from the same source region were found in all these events. Furthermore, these two CMEs overlapped partially with each other in their propagating path, which were consistent with "twin-CME" scenario. In these events, we also checked the process of CMEs erupting from their source region in low corona, such as the association of type II radio bursts, the associated AIA multi-waveband images on board SDO apacecraft, HMI magnetogram and the magnetic field from the extrapolated Non-Linear Force Free Field (NLFFF) model, and confirmed that these preceding CMEs were not the early phase of the main CME in "twin-CME" observations.Second, we examined126fast CMEs having western hemisphere source regions in Salor Cycle23, which included59CMEs that led to large SEP events. The statistical results indicate that the peak flux intensities of these SEP events associated with "twin-CME" eruptions did not seem to be correlated with the speed of the associated fast CMEs, the class of associated flares, and the daily (24hr) average seed population prior to SEPs onset time. However, for single-CME events, the peak flux intensity of the SEPs and these three parameters had distinct positive correlations. This can be understood naturely within "twin-CME" scenario:the presence of preceding CMEs can previde enough seed population for the main fast CME shock acceleration, so there is no need to have a high CME speed and/or intense flare and/or the seed particles prior to event. The results also indicate that there is a strong correlation between "twin-CME" and the large SEP events, and suggest that the probability of a "twin-CME" event leading to large SEP events (such as the events with peak flux>10pfu at10MeV channel) is significantly higher than "single-CME" events.Third, we tried to answer several questions about SEP events:1). The choice of the time interval threshold between preceding CME and main CME, we decide this parameter by examining the tendency of the percentage of the SEP events caused by "twin-CME" eruptions among all SEP events by varying this time interval, and by examining how the probability of single fast CMEs failing to generate large SEP events as a function of this time interval. We chose the time threshhold between1hr to24hr with a bin of1hr. The time of-12hr turns out to be a best choice.2). Using the Velocity Dissipation Analysis (VDA) method, we found that the starting release heights of solar energetic particles from low corona is less than15Rsun. In these heights, the preceding CME can provide seed population more effectively for the main CME than a preceding flare, because the turbulence stimulated by the preceding CME shock can held more seed particles for a longer time ahead of the main fast CME.3). Our findings about type II radio bursts in this paper were shown that there is no indicative difference between SEP events and no SEP events, but the proportion of type II radio bursts associating CME with large SEP events is higher than that of the CMEs with no SEP events.4). We discussed the longitudinal dependence of time delay and enhancement slope of SEP flux profiles for different relative longtitudes comparing to the earth-well-connected footpoint. The more eastern relative longitudes comparing to the footpoints, the longer time delay of SEP onset from background to peak and the slower enhancement slope of SEP flux. This implies that the SEP events with eastern source region usually have weaker intensity and lower peak flux than western events.In conclusion, we analyzed the causal association between SEP events and CME eruptions through a comprehensive set of observations. We find that the "twin-CME" erupting consecutively from the same region usually leads to a large SEP events more effectively than a single fast CME. In the "twin-CME" scenario, the traditional variables (such as speed of associated fast CME, or associated flare class et al.) are not deciding factors for the resulting SEP intensity, but the presence of a preceding CME is. We also suggest that the reference value of "twin-CME" time interval between main CME and preceding CME can be set to12hr.更多还原