A great geomagnetic storm occurred around 1640 UT on April 6, 2000,with a value of -317 nT in Dst index. The responses of the ionosphereat Wuhan during the first stage of this storm were reported in thispaper. Soon after the sudden storm commencement (SSC) at 1640 UT, themain phase of the geomagnetic storm appeared, and the storm stepped intoits recovery phase at the beginning of the next day. A rapid and largeincrease in the ionospheric heights at Wuhan occurred at the beginningof the main phase, and the lifts in h′F and hmF2 lasted for about 2hours. The value of f0F2 decreased about 1.6 MHz at the beginningof the main phase, and the maximum value of f0F2 on the next day wasless than that on April 5 more than 3 MHz at Wuhan. Thealmost simultaneous increase in h′F was also observed at Chungli, Taiwan.The near simultaneity of the h′F disturbances at the two stationssuggested that an E B plasma drift due to an east-westelectric field of storm origin was the cause of the rapid and largelifts in the nighttime ionospheric heights after the SSC.%2000年4月6---7日的大磁暴(Dst最小值达到-317 nT),急始(SSC)在6日1640 UT左右出现,随后磁暴主相开始,约在7日0013 UT进入恢复相.磁暴主相前期武汉地区F区电离层出现突然抬高现象,在2 h内h′F和hmF2分别较暴前日增加约200 km.此期间台湾中沥也几乎同时出现了F区电离层突增现象.磁暴主相前期f0F2较暴前日下降1.6 MHz,其变化幅度在f0F2逐日变化起伏范围内,但7日f0F2最大值明显低于4---6日暴前水平,并伴随着波动特征.认为此次磁暴主相前期武汉地区F区电离层突增现象,可能和夜间磁暴常出现的扰动东向电场有关.
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