Geomagnetically induced currents (GICs) are driven by the geoelectric field induced by fluctuations of Earth's magnetic field. Drivers of intense GICs are often associated with large impulsive events such as coronal mass ejections. To a lesser extent fluctuations from regular oscillations of the geomagnetic field, or geomagnetic pulsations, have also been identified as possible drivers of GICs. In this work we show that these low‐frequency pulsations are directly observed in measured GIC data from power networks. Due to the low‐pass nature of GICs, Pc5 and lower‐frequency pulsations drive significant GICs for an extended duration even at midlatitudes. Longer‐period Ps6‐type disturbances apparently not typical of midlatitudes are seen with GIC amplitudes comparable to the peak GIC at storm sudden commencement. The quasi‐ac (alternating current) nature of the sustained pulsation driving affects the power system response and cannot be properly modeled using only direct current (dc) models. A further consideration is that the often used dB/dt GIC proxy is biased to the sampling rate of the geomagnetic field measurements used. The dB/dt metric does not adequately characterize GIC activity at frequencies in the low ultralow‐frequency (ULF) range, and a frequency‐weighted proxy akin to geoelectric field should be used instead.

中文翻译：

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地磁脉动驱动地磁感应电流

地磁感应电流（GIC）由地球磁场波动感应的地电场驱动。强烈的GIC的驱动程序通常与大的冲动事件相关联，例如日冕物质抛射。在较小程度上，地磁场的规则振荡或地磁脉动引起的波动也被确定为GIC的可能驱动因素。在这项工作中，我们表明，这些低频脉动可以直接在来自电网的GIC数据中观察到。由于GIC的低通特性，即使在中纬度地区，Pc5和低频脉动也会在较长时间内驱动重要的GIC。在风暴突然开始时，GIC振幅可与峰值GIC相媲美，这在中纬度地区似乎不常见更长时期的Ps6型干扰。持续脉动驱动的准交流（交流）特性会影响电源系统的响应，因此无法仅使用直流（dc）模型进行正确建模。进一步的考虑是，经常使用d B / d t GIC代理偏向使用的地磁场测量的采样率。所述d乙/ d吨度量在低超低频率（ULF）的频率范围内，和频率加权代理类似于地电场，而应使用没有充分表征GIC活性。