多方向μ介子通量一致性特征研究

Study of Multi-directional Muon Flux in Geomagnetic Storm Prediction

通过地面μ介子望远镜可以探测不同方向到达的宇宙线通量,得到从外空间入射的宇宙线受到不均匀结构的调制情况,判断CME的特征.通过分析,发现大地磁暴前Nagoya台站东向和南向的探测数据存在固定的2h时间差,认为这是由两个入射方向的宇宙线粒子先后穿越CME结构引起的.分别计算了两个方向相同时间和南向相位后移2h后通量探测数据的相关系数,以及两种情形下通量差的变化幅度,定量描述了CME接近地球过程中两个方向通量的相关特征.通过比较发现,CME接近地球过程中,经过相位变换的两个方向的相关系数明显高于未经变换的情况,经过相位变换的两个方向的通量差幅度明显小于未经变换的情况;CME到达地球后,两种情形的相关系数和通量差幅度则趋于相同.对2003-2005年Kp=9的地磁暴事件的分析均发现了这种现象.对2006年12月14日大地磁暴前的μ介子通量特征进行了分析,也完全符合上述特征.

By analyzing the characteristics of cosmic ray flux evolution, the approaching of CMEs could be identified, and the geomagnetic disturbance could be forecasted. The modulation of cosmic by CMEs could be derived by comparing the fluxes from different directions, and the parameters, such as Interplanetary Magnetic Field （IMF） and direction, could be derived. In this paper, data obtained by Nagoya muon telescope are used, and southward and eastward flux are chosen for investigation in detail. The results show that the evolutions of muon fluxes from the two directions share similarpattern before the strong geomagnetic storm, while there is a 2-hour phase delay between them. It is analyzed that the cosmic rays corresponding to the two directions went into and out the CME successively and the time difference is about 2 hours. The correlation coefficient and flux difference of the fluxes in eastern and southern, concluding the phase of the southern flux is moved backward two hours or not, are calculated respectively. As CMEs approaching, the correlation coefficient with southward phase change is significantly higher than that without phase change, and the flux difference with the southward phase change is much lower than that without phase change. However, the coefficient and the flux difference began to get close to each other when CMEs arrive at the Earth. And the above parameters of phase changed disparity amplitude even exceeded the unchanged one. The characteristics are also found in the geomagnetic storms with Kp = 9 from 2003 to 2005. The muon flux before the great geomagnetic storm on December 14, 2006 is analyzed, and the study found that it is coincident with the above characteristics. Therefore, directional muon detection possesses a unique ability to remote sensing CMEs propagation through the difference of the flux evolution from different directions.