特大地磁暴的一种行星际源:多重磁云

2001年3月31日观测到的大的多重磁云(Multi MC)事件造成了第23周太阳峰年(2000～2001)最大的地磁暴(Dst=-387nT). 通过分析ACE飞船的观测数据, 描述了这个多重磁云在1AU处的磁场和等离子体特征. 并且根据SOHO和GOES卫星的观测资料, 认证了它的太阳源. 在这次事件中, 由于多重磁云内部异常增强的南向磁场, 使之地磁效应变得更强, 它大大的延长了地磁暴的持续时间. 观测结果与理论分析表明, 多重磁云中子磁云的相互挤压使磁云内的磁场强度及其南向分量增强数倍, 从而加强了地磁效应. 因此, 研究认为多重磁云中子磁云之间的相互压缩是造成特大地磁暴的一种机制. 此外, 研究发现形成多重磁云的日冕物质抛射(CMEs)并不一定要来自同一太阳活动区.

An interplanetary origin of great geomagnetic storms: Multiple magnetic clouds

An event of multiple magnetic cloud (Multi MC) in interplanetary space on March 31, 2001 caused the largest geomagnetic storm with Dst=-387 nT during the 23th solar maximum (2000～2001). By analyzing the data from the ACE spacecraft, we describe the characteristics of the magnetic fields and plasma within this Multi MC at 1 AU. We also identify its solar sources, namely coronal mass ejections (CMEs). by utilizing the observations from the Solar and Heliospheric Observatory (SOHO) and the GOES satellite. In this instance, the Multi MC became more effective with the extraordinary enhanced southward magnetic fields, and largely extended the duration of the Dst storm. The observations and the theoretical analysis reveal that the strength of the magnetic fields including the southward component increased several times due to the compression between the sub clouds in the Multi MC, and therefore intensified the corresponding effectiveness of geomagnetism. Thus, we suggest that the compression between the sub clouds of Multi MC should be a mechanism in causing great geomagnetic storms. In addition, we find that the CMEs, which formed the Multi MC, seemed not to originate from the same solar region.