中文摘要：

利用Cluster卫星的磁场探测数据及ACE卫星的行星际磁场（IMF）探测数据,研究了IMF B_y分量（IMF｜B_y｜〈10nT）对磁尾等离子体片边界层（PSBL）区场向电流发生率和密度的影响.研究显示：与IMF B_y分量为负时进行比较,IMF B_y分量为正时场向电流的发生率更高,约55.6%;当IMF｜B_y｜〉4nT时场向电流发生率占总发生率的77.4%;场向电流发生率随IMF｜B_y｜的增大而增大,且具有很好的线性相关关系,当IMF B_y分量为正时,相关性更好;场向电流密度也随IMF｜B_y｜的增大而增大,同样具有很好的线性相关关系,当IMF B_y分量为正时,相关性更好.以上结果表明,IMF B_y分量对磁尾场向电流的产生和变化具有很强的控制作用,并且昏向IMF变化与场向电流变化的关系更加密切.

英文摘要：

Using the magnetic field data from Cluster spacecraft and the Interplanetary Magnetic Field（IMF） data from ACE spacecraft,the effect of IMF B_y component（IMF ｜B_y｜ 10nT） on the Field-Aligned Current（FAC） occurrence rate and density at the Plasma Sheet Boundary Layer（PSBL） in the magnetotail is investigated.1657 FAC cases from July to October in 2001 and 2004 were selected for analysis.We present that the IMF B_y component plays a very important role in controlling the occurrence rate and density of the FAC in the PSBL in the magnetotail.The FAC occurrence is higher（about 55.6%） when the IMF B_y is positive compared with that when the IMF B_y is negative.When the IMF ｜B_y｜ is more than 4nT,the occurrence rate of FAC is about 77.4%.The FAC occurrence in the magnetotail has an obvious positive correlation with the IMF ｜B_y｜,and when the IMF B_y is positive,this correlation is better.The FAC density also has an obvious positive correlation with the IMF ｜B_y｜,and when the IMF B_y is positive,this correlation is better.The above results show that the IMF B_y component has strong control on the occurrence and density of the FAC cases in the magnetotail,and that the change of FAC is closely associated with the duskward IMF（the IMF B_y is positive）.