The ionosonde at the Sodankylä Geophysical Observatory (SOD; 67^∘ N, 27^∘ E; Finland) routinely performs vertical sounding once per minute which enables the study of fast ionospheric variations at a frequency of the long-period geomagnetic pulsations Pc5–6/Pi3 (1–5 mHz). Using the ionosonde data from April 2014–December 2015 and colocated geomagnetic measurements, we have investigated a correspondence between the magnetic field pulsations and variations of the critical frequency of radio waves reflected from the ionospheric F2 layer (foF2). For this study, we have developed a technique for automated retrieval of the critical frequency of the F2 layer from ionograms. As a rule, the Pc5–6/Pi3 frequency band fluctuations in foF2 were observed at daytime during quiet or moderately disturbed space weather conditions. In most cases (about 80 %), the coherence between the foF2 variations and geomagnetic pulsations was low. However in some cases (specified as “coherent”) the coherence was as large as γ²≥0.5. The following conditions are favorable for the occurrence of coherent cases: enhanced auroral activity (6 h maximal auroral electrojet (AE) ≥800 nT), high solar wind speed (V>600 km/s), fluctuating solar wind pressure and northward interplanetary magnetic field. In the cases when the coherence was higher at shorter periods of oscillations, the magnetic pulsations demonstrated features typical for the Alfvén field line resonance.

中文翻译：

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即使是中等的地磁脉动也会引起极光电离层fo F2频率的波动

Sodankylä 地球物理天文台 (SOD; 67 ^∘  N, 27 ^∘  E; 芬兰) 的电离探空仪通常每分钟进行一次垂直探测，这使得能够以长周期地磁脉动 Pc5-6/Pi3 的频率研究快速电离层变化（1–5 兆赫兹）。从2014年4月，2015年12月和同一位置地磁测量使用电离层探测仪的数据，我们已经调查了磁场脉动和从电离层F2层（反射的无线电波的临界频率的变化之间的对应关系FO F2）。在这项研究中，我们开发了一种从电离图中自动检索 F2 层临界频率的技术。通常，Pc5-6/Pi3 频带波动在foF2 是在白天安静或中度扰动的太空天气条件下观察到的。在大多数情况下（大约80  %），fo F2 变化和地磁脉动之间的相干性很低。然而，在某些情况下（指定为“相干”），相干性与γ ² ≥0.5一样大。以下条件有利于相干情况的发生：极光活动增强（6 h最大极 光电射流（AE） ≥800 nT），太阳风速高（V >600 km/s)、波动的太阳风压和向北的行星际磁场。在较短振荡周期内相干性较高的情况下，磁脉动表现出阿尔文场线共振的典型特征。