In the United Kingdom, geomagnetically induced currents (GICs) are calculated from thin‐sheet electrical conductivity models. In the absence of conductivity models, time derivatives of magnetic fields are sometimes used as proxies for GIC‐related electric fields. An alternative approach, favored in the United States, is to calculate storm time electric fields from time‐independent impedance tensors computed from an array of magnetotelluric (MT) sites and storm time magnetic fields recorded at geomagnetic observatories or assumed from line current models. A paucity of direct measurements of storm time electric fields has restricted validation of these different techniques for nowcasting electric fields and GICs. Here, we present unique storm time electric field data from seven MT sites in Scotland that recorded before, during, and after the September 2017 magnetic storm. By Fourier transforming electric field spectra computed using different techniques back to the time domain, we are able to make direct comparisons with these measured storm time electric field time series. This enables us to test the validity of different approaches to nowcasting electric fields. Our preferred technique involves frequency domain multiplication of magnetic field spectra from a regional site with a local impedance tensor that has been corrected for horizontal magnetic field gradients present between the local site and the regional site using perturbation tensors derived from geomagnetic depth sounding (GDS). Scatter plots of scaling factors between measured and nowcasted electric fields demonstrate the importance of coupling between the polarization of the storm time magnetic source field and Earth's direction‐dependent deep electrical conductivity structure.

中文翻译：

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使用大地电磁数据临近预报和验证地球电场对极端空间天气事件的响应：应用于2017年9月的地磁风暴以及与苏格兰观测和模拟场的比较

在英国，地磁感应电流（GIC）是根据薄板电导率模型计算得出的。在没有电导率模型的情况下，有时将磁场的时间导数用作GIC相关电场的代理。在美国最受欢迎的另一种方法是，根据与时间无关的阻抗张量来计算风暴时间电场，该时间张量是由大地电磁（MT）站点的阵列计算出来的，以及在地磁观测站记录的或由线电流模型假定的风暴时间磁场。由于缺乏直接测量风暴时间电场的能力，因此限制了这些用于临近电场和GIC的不同技术的验证。在这里，我们展示了来自苏格兰七个MT站点的独特风暴时间电场数据，这些数据是在 在2017年9月的磁暴之后。通过对使用不同技术计算出的电场谱进行傅立叶变换回到时域，我们能够与这些测得的风暴时间电场时间序列进行直接比较。这使我们能够测试临近电场的不同方法的有效性。我们的首选技术涉及使用局部阻抗张量对区域站点的磁场频谱进行频域乘法，该局部阻抗张量已使用源自地磁深度探测（GDS）的扰动张量针对存在于局部站点和区域站点之间的水平磁场梯度进行了校正。