行星际磁场对极尖区位形变化的统计研究

利用Cluster卫星数据，选取2001—2010年期间的616个极尖区穿越事件，研究了行星际磁场（IMF）的大小和方向对极尖区位形的影响.结果表明：当B_z为北向时，随着B_x负向的增大，极尖区的磁不变纬度向高纬方向（极区）移动；当B_z为南向时，随着B_x负向增大，极尖区的磁不变纬度略微向低纬度方向（赤道）移动.B_x正向增大时，极尖区并没有明显移动.B_x对极尖区影响在南半球较为显著，在北半球没有明显规律性变化.此外，随着行星际磁场锥角的增大（>90°），极尖区也随之向高纬移动.当B_z南向时，随着B_y的负向增大，极尖区在北半球向晨侧移动，在南半球向昏侧移动.而当B_z南向增加时，南北半球两个极尖区的磁不变纬度都朝赤道方向移动；但北向B_z时几乎没有移动.

Cusp location dependence on IMF: Cluster statistical study

The 616 mid and high altitude cusp crossings, collected from Cluster observation for the time interval from 1st February 2001 to 31st December 2010, are used to study IMF effect on cusp locations. Our results show that with the increasing of the negative B_x, the invariant latitude of the cusp moves to poleward for northward IMF, while it slightly shifts equatorward for southward IMF. For the increasing positive B_x, the invariant latitude of the cusp doesn't change too much. This phenomenon is observed obviously for the southern hemisphere, but no apparent phenomenon occurs on the northern hemisphere. When cone angle is greater than 90°, the southern cusp has a polarward movement with increasing cone angle. Moreover, when the negative B_y is enhanced, the magnetic local time of cusp turns dawnward (duskward) for northern (southern) hemisphere under southward IMF. Consistent with previous study, we also find that with the increasing of southward B_z, the invariant latitude of the cusp moves equatorward for both northern and southern hemisphere, while it keeps almost unchanged for northward B_z.