中文摘要：

利用EISCAT VHF和EISCAT Svalbard（ESR）雷达观测数据，对2003年2月12日IMF Bz分量4次快速方向转换期间，极区电离层，尤其是极尖／极隙区的响应特征进行了分析研究．随着IMF Bz方向的多次快速变化，地面雷达观测到极尖／极隙区所在位置随着开放-闭合磁力线边界在纬度方向上来回移动．在此期间，极区电离层等离子体水平对流多次反向，表现出与IMF Bz分量强的负相关性．进一步分析表明：极区磁层-电离层系统在日侧对IMF极性变化的平均响应时间约为3min．

英文摘要：

Abstract With the observations from EISCAT/ESR radar on Feb. 12 2003, the responses of polar ionosphere, especially those of the cusp/cleft region to the 4-times rapid turnings of IMF Bz component are investigated in this paper. During this event, latitudinal location of the cusp/cleft region was found moving back and forth, likely resulted from the variations of the reconnection sites at the magnetopause which are widely accepted to be ruled by the IMF polarity. Meanwhile, polar ionospheric plasma convection reversed several times, exhibiting strong correlation with the signs of the IMF B~ component. Correlative and timing analysis suggest that the dayside magnetosphere-ionosphere system seems to need an average reconfiguration time of approximate 3 minutes in response to the variations of the IMF polarity in polar region.