Changes in the Earth's geomagnetic field induce geoelectric fields in the solid Earth. These electric fields drive Geomagnetically Induced Currents (GICs) in grounded, conducting infrastructure. These GICs can damage or degrade equipment if they are sufficiently intense—understanding and forecasting them is of critical importance. One of the key magnetospheric phenomena are Sudden Commencements (SCs). To examine the potential impact of SCs we evaluate the correlation between the measured maximum GICs and rate of change of the magnetic field (H′) in 75 power grid transformers across New Zealand between 2001 and 2020. The maximum observed H′ and GIC correlate well, with correlation coefficients (r²) around 0.7. We investigate the gradient of the relationship between H′ and GIC, finding a hot spot close to Dunedin: where a given H′ will drive the largest relative current (0.5 A nT⁻¹ min). We observe strong intralocation variability, with the gradients varying by a factor of two or more at adjacent transformers. We find that GICs are (on average) greater if they are related to: (a) Storm Sudden Commencements (SSCs; 27% larger than Sudden Impulses, SIs); (b) SCs while New Zealand is on the dayside of the Earth (27% larger than the nightside); and (c) SCs with a predominantly East-West magnetic field change (14% larger than North-South equivalents). These results are attributed to the geology of New Zealand and the geometry of the power network. We extrapolate to find that transformers near Dunedin would see 2000 A or more during a theoretical extreme SC (H′ = 4000 nT min⁻¹).

中文翻译：

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新西兰的突然开始和地磁感应电流：相关性和依赖性

地球地磁场的变化在固体地球中感应出地电场。这些电场在接地导电基础设施中驱动地磁感应电流 (GIC)。如果这些 GIC 足够强烈，它们可能会损坏或降低设备性能 - 理解和预测它们至关重要。关键的磁层现象之一是突然开始（SC）。为了检查 SC 的潜在影响，我们评估了2001 年至 2020 年间新西兰 75 个电网变压器中测得的最大 GIC 与磁场变化率 ( H ' ) 之间的相关性。观测到的最大H ' 和 GIC 具有良好的相关性，相关系数 ( r ² ) 约为 0.7。我们研究了H ' 和 GIC之间关系的梯度，找到了达尼丁附近的一个热点：给定的H ' 将驱动最大的相对电流（0.5 A nT ^-1 分钟）。我们观察到强烈的位置内变异性，相邻变压器处的梯度变化为两倍或更多倍。我们发现，如果 GIC 与以下方面相关，则它们（平均）会更大： (a) 风暴突然开始 (SSC；比突然冲动，SI 大 27%)；(b) 新西兰位于地球的昼面时的 SC（比黑面大 27%）；(c) SC 的磁场变化主要为东西向变化（比南北向磁场变化大 14%）。这些结果归因于新西兰的地质和电网的几何形状。我们推断发现达尼丁附近的变压器在理论上的极端 SC ( H ′ = 4000 nT min ⁻¹ ) 期间会出现 2000 A 或更多。