利用Cluster Ⅱ数据分析等离子体片区磁结构运动特性

利用Cluster Ⅱ 卫星上搭载的磁通门磁强计的观测数据，可以计算磁结构的运动速度.本文在GSM（Geocentric Solar Magnetospheric System，地心太阳磁层系）坐标系下处理了磁暴期间（2002年8月1日到2日）和磁场宁静期（2002年8月6日到7日）的等离子体片区的观测数据.通过分析磁结构速度的统计特性和频谱特性，得到以下结论：（1）磁结构运动速度呈现出不规则的摆动结构.（2）Vz的方差与Vy的方差近似相等，而远大于Vx的方差.这可能是由于“风袋效应”.（3）在黎明侧的等离子体片区, Vx和Vz的平均值约为0，但Vy的平均值的量级为-10 km/s.这可能是在等离子体片区Pc5压缩波造成的.（4）Vx, Vy, Vz的频谱在0033 min-1和0035 min-1之间都有一个峰值.

Movement of the magnetic structure in the plasma sheet observed by Cluster Ⅱ

Using the data of the FGM instrument onboard of Cluster Ⅱ, we can calculate the velocity of the magnetic structure. Data observed by Cluster Ⅱ in the plasma sheet were analyzed during the storm (1 and 2 August 2002) and the geomagnetism quiet (6 and 7 August 2002) in GSM coordinates. Analysis of statistical characteristics and spectral characters of the velocity shows that the variation of the velocity is an irregular oscillation. The width of the distribution of Vz is nearly equal to that of Vy and they are both larger than that of Vx. This may be caused by the windsock mechanism. On the dawn side of the plasma sheet, the average of Vx and Vz are nearly equal to 0，but the average of Vy is in the order of －10 km/s. It may be caused by the compressed Pc5 wave which moves in the plasma sheet. All the spectra of Vx, Vy, Vz have their own peaks between 0033 min-1 and 0035 min-1