2001年1月26日高纬磁层顶通量管事件的观测研究

2001年1月26日11:10～11:40UT， ClusterⅡ卫星簇位于午后高纬磁鞘边界层和磁鞘区，此 时行星际磁场Bz为南向. 本文对在此期间观测到的多次磁通量管事件作了详细的研究 ，获得一系列的新发现：（1）高纬磁鞘边界层磁通量管的出现具有准周期性，周期约为78s ，比目前已知的磁层顶向阳面FTE的平均周期（8～11min）小得多. （2）这些通量管都具有 强的核心磁场；其主轴多数在磁场最小变化方向，少数在中间变化方向，有些无法用PAA判 定其方向（需要用电流管PAA确定），这与卫星穿越通量管的相对路径有关. （3）每个事件 都存在很好的HT参考系，在HT参考系中这些通量管是准定常态结构；所有通量管都沿磁层顶 表面运动，速度方向大体相同，都来自晨侧下方. 通量管的径向尺度为1～2RE, 与通 常的FTE通量管相当. （4）起源于磁层的强能离子大体上沿着管轴方向由磁层向磁鞘运动； 起源于太阳风的热等离子体沿管轴向磁层传输. 通量管为太阳风等离子体向磁层输运和磁层 粒子向行星际空间逃逸提供了通道. （5）每个通量管事件都伴随有晨昏电场的反转，该电 场为对流电场.

MULTIPLE FLUX ROPE EVENTS AT THE HIGH-LATITUDE MAGNETOPAUSE:CLUSTER/RAPID OBSERVATIONS ON JANUARY 26, 2001

From 11:10 to 11:40UT on January 26, 2001 four Cluster-II spacecrafts were located in the dusk- side high latitude regions of the magnetosheath and the magnetosheath boundary layer. During this time interval the interplanetary magnetic field (IMF) had a negative B z component. A detailed study on the multiple flux ropes (MFRs) observed in this time period is conducted in this paper. It is found that the MFRs in the high latitude magnetosheath boundary appeared quasi-periodically with a repeated time period of about 78s, which is much shorter than the averaged occurrence period (about 8-11 minutes) of the flux transfer events (FTEs) at the dayside magnetopause. All the flux ropes observed in this event had a strong core magnetic field. The principal axis of the most flux ropes are found to lie in the direction of the minimum magnetic field variation. A few flux ropes had their axes lying in the direction of the middle magnetic field variation; while for the remainders their principle axes could not be determined by the method of Principal Axis Analysis (PAA). The reason that causes this complexity relays on the different trajectories of the spacecraft passing through the flux ropes. Each flux rope had a good corresponding HT frame of reference in which it was in a quasi-steady state. All flux ropes moved along the surface of the magnetopause in a similar direction indicating that these flux ropes were coming from the dawnside low latitude. Their radial scale is found to be 1-2R E, comparable to the normal diameter of FTEs. The energetic ions originated from the magnetosphere were flowing out to the magnetosheath on the whole, while the solar wind plasma was seen to flow into the magnetosphere along the axis of the flux ropes. The flux ropes offered channels for the transport of the solar wind plasma into the magnetosphere and the escape of the magnetospheric plasma into the interplanetary space. Each event was accompanied by an enhanced reversal of the dusk-dawn electric field, which could be identified to be the convective electric field in nature.