We examine how Sudden Commencements (SCs) and Storm Sudden Commencements (SSCs) influence the occurrence of high rates of change of the magnetic field (R) as a function of geomagnetic latitude. These rapid, high amplitude variations in the ground-level geomagnetic field pose a significant risk to ground infrastructure, such as power networks, as the drivers of geomagnetically induced currents. We find that rates of change of ∼30 nT min⁻¹ at near-equatorial stations are up to 700 times more likely in an SC than in any random interval. This factor decreases with geomagnetic latitude such that rates of change around 30 nT min⁻¹ are only up to 10 times more likely by 65°. At equatorial latitudes we find that 25% of all R in excess of 50 nT min⁻¹ occurs during SCs. This percentage also decreases with geomagnetic latitude, reaching ≤1% by 55°. However, the time period from the SC to 3 days afterward accounts for ≥90% of geomagnetic field fluctuations over 50 nT min⁻¹, up to ∼60° latitude. Above 60°, other phenomena such as isolated substorms account for the majority of large R. Furthermore, the elevated rates of change observed during and after SCs are solely due to those classified as SSCs. These results show that SSCs are the predominant risk events for large R at mid and low latitudes, but that the risk from the SC itself decreases with latitude.

中文翻译：

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突然开始对地面磁场变化的影响：直接和延迟后果

我们研究了突然开始 (SC) 和风暴突然开始 (SSC) 如何影响作为地磁纬度函数的磁场( R )高变化率的发生。地面地磁场的这些快速、高振幅变化对作为地磁感应电流的驱动器的地面基础设施（例如电力网络）构成了重大风险。我们发现，在近赤道站，大约30 nT min ^-1的变化率在 SC 中比在任何随机间隔中的可能性高 700 倍。该因素随着地磁纬度而降低，使得大约 30 nT min ^-1的变化率在65° 时仅增加 10 倍。在赤道纬度，我们发现所有R 的25%超过 50 nT min ^-1发生在 SCs 期间。这个百分比也随着地磁纬度而降低，55°时达到≤1%。然而，从 SC 到 3 天之后的时间段占了 50 nT min ^-1上地磁场波动的 90% 以上，直到纬度约 60°。在 60° 以上，其他现象（例如孤立的亚暴）占大R的大部分。此外，在 SCs 期间和之后观察到的变化率升高完全是由于那些被归类为 SSCs。这些结果表明，SSCs 是中低纬度地区大 R 的主要风险事件，但来自 SC 本身的风险随纬度降低。