Abstract—

Based on an analysis of the F2-layer critical frequency (foF2) at Irkutsk station during the extreme storm of March 13–15, 1989, it is found that geomagnetic activity index aa is a more adequate indicator than ap for foF2 during the maximum of an extreme storm. This is related to the existence of the upper limit of changes in ap (ap = 400) and this fact imposes some limitations on using the ap index for extreme events. In the initial period of the recovery phase of the considered storm, a rapid decrease of geomagnetic activity occurred. A strong deviation of the experimental values of foF2 from the values calculated by the semi-empirical model, which considers the dependences of the thermospheric temperature and composition on geomagnetic activity by the NRLMSISE-00 atmospheric model, was observed during that period. It is assumed that this could be related to the effect of disturbance of thermospheric wind velocity due to the rapid decrease of geomagnetic activity. This assumption is rather qualitative and requires a special study.

中文翻译：

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极端风暴期间电离层的性质

摘要-

根据对1989年3月13日至15日极端风暴期间伊尔库茨克站F 2层临界频率（foF 2）的分析，发现地磁活动指数aa比ap对foF 2更适合极端风暴的最大值。这与ap（ap = 400）的变化上限的存在有关，并且这一事实对极端事件使用ap索引施加了一些限制。在考虑的风暴恢复阶段的最初阶段，地磁活动迅速下降。foF实验值有很大偏差从半经验模型计算的值中可以看出，在此期间观测到了NRLMSISE-00大气模型对热层温度和成分对地磁活动的依赖性的半经验模型。假定这可能与由于地磁活动迅速下降而引起的热层风速扰动有关。这种假设是定性的，需要进行特殊研究。