2004年3月18日高纬磁层顶多重通量管事件分析

A further study of multiple flux rope events at the magnetopause observed by TC-1 on 18 March 2004

2004—03—18 23：10-23：50UT期间，“双星（Double Star）”探测一号卫星（TC-1）在向阳面磁层顶高纬晨侧由内向外穿越磁层顶，其时TC-1的GSM坐标为（7．5RE，-5．5RE，-5．4RE），RE为地球半径．穿越过程中TC-1观测到了8个通量管和1个磁通量传输事件（FTEs）．在此期间Cluster星簇位于向阳面太阳风内，其GSM坐标为（18．0RE，-3．1RE，-6．2RE），其4颗卫星监测到行星际磁场（IMF）的易分量持续南向，毋有较大的负值．本文的研究表明：TC-1观测到的前7个通量管具有准周期重现性，周期大约是1—4min，明显小于以前所观测到的FTEs的平均周期（8-11min）；所有的通量管都具有较强的核心场．本文分别使用最小方差分析法（MVA）和Grad-Shafranov反演方法（GSR）对通量管的轴向进行了分析和对比，发现所有的通量管主轴基本沿晨昏向，结果显示GSR方法在轴向分析上比MVA优越．本文使用GSR方法对通量管的磁场结构进行了分析，恢复出了通量管的磁场在卫星穿越面的结构图；此外，本文还对这次多重通量管事件进行了deHoffmann-Teller（HT）分析，结果表明，所有通量管大致朝南极方向运动，均来源于向日面低纬区域．这说明它们可能起源于向日面低纬区，由该区的磁场分量重联产生．

From 23：10 to 23：50 UT on 18 March 2004, the Double Star TC-1 spacecraft detected nine flux ropes at the outbound crossing of the southern dawnside magnetopause. During this time period the Cluster constellation was staying in the magnetosheath. The four spacecraft observed that the interplanetary magnetic field （IMF） has a dominant negative By component together with a southward Bz. Notable guide field was found to exist inside all eight magnetic flux ropes detected by TC-1. The precedent seven ropes observed from 23：14- 23：27 UT that appeared quasi-periodically with a repeated period being approximately 1 -4 minutes, which is much shorter than the averaged occurrence period （about 8- 11 minutes） of the flux transfer events （FTEs） at the dayside magnetopause. The Minimum Variation Analysis （MVA） and the Grad-Shafronov Reconstruction （GSR） technique are applied in the present study of this multiple flux rope events. By is large, all the principal axes of this flux ropes are found to be along the dawn-dusk direction. The deHoffmann-Teller （HT） analysis shows that the HT velocities （VHT） of these flux ropes were all directed dawnward and poleward, indicating that they came from the duskward and equatorward side of the spacecraft location and were produced via component magnetic reconnection in the subsolar region at the magnetopause.