全球电离层对2000年4月6-7日磁暴事件的响应

利用分布于全球的电离层台站的测高仪观测数据，对扰动期间，foF2值与其宁静期间参考值进行比较，研究了2000年4月6—7日磁暴期间全球不同区域电离层的响应形态，并通过对比磁扰期间NmF2的变化与由MSISR90经验模式估算的中性大气浓度比(no／nN2)的变化，探讨了本次事件期间的电离层暴扰动机制．结果表明，在磁暴主相和恢复相早期，出现了全球性的电离层F2层负相暴效应．最大负相暴效应出现在磁暴恢复相早期，即电离层暴恢复相开始时间滞后于磁暴恢复相开始时间．在磁暴恢复相后期，一些台站出现正相扰动．研究结果表明，本次事件期间的电离层暴主要是由磁暴活动而诱发的热层暴环流引起的．

Global Ionospheric Response to the Geomagnetic Storm Event of April 6-7, 2000

A great geomagnetic storm occurred during April 6-7, 2000, with the Dst index reaching a minimum value of about-320 nT. Using the ionosonde and digisonde data from about 25 stations distributed globally, the morphology of the ionospheric response to this geomagnetic storm event is studied by comparing the storm-time disturbed value of f0F2 with its quiet time reference value. To identify the mechanism responsible for the ionospheric disturbances during this event, a comparison is made between the ratio of disturbed to undisturbed values of NmF2 and of the neutral composition concentration ratio (no/nN2). The results of data analysis showed that during the main and early recovery phases of the geomagnetic storm, a negative ionospheric F2 layer storm occurred globally. The maximum negative deviation of f0F2 from its quiet time reference value occurred during the early recovery phase of the geomagnetic storm. During the late recovery phase of the geomagnetic storm, positive ionospheric disturbances occurred in some stations, particularly in those high latitude stations. It is showed that the main characteristics of the ionospheric disturbances during this geomagnetic storm event are consistent with that expected from the storm effects resulted from storm-induced thermospheric circulation system.