Investigating the Drivers of Geomagnetically Induced Currents

地球磁场位于多变、动态的太阳风环境中。这两个机制的相互作用推动了地球磁场的快速重新配置，从而诱导电流在地面上的导体中流动。这些地磁感应电流(GIC)可达10s至100s安培，可导致电网中的变压器发热和更高的谐波、金属管道退化，以及铁路系统的信号故障。Lloyd‘s of London 2013 Space Weather报告的结论是，一场百年一遇的事件“将对交通、食品供应、应急和医院服务等造成重大干扰……缺乏这些基本服务可能会导致重大而广泛的社会动荡、骚乱和盗窃，对保险业和整个社会产生影响”。据估计，这类事件对英国造成的损失约为9亿至159亿GB，虽然这样的大事件很少见，但规模较小的破坏性事件是经常被观察到的。预测GIC的位置和强度的关键是了解从太阳到地球表面的因果链，并在关键位置配备仪器来进行预测所需的测量。已经确定了驱动强大GIC的典型太阳风结构，并可以为地球系统中的极端动力学提供一些早期预警。链的另一端，由于可变磁场而在地面导体中感应电流，可以通过应用法拉第定律来解决，给定局部地层的电导率，以及导体的电导率、长度和取向。通常情况下，这项研究是由专注于本国关键基础设施运营风险的单个国家资助的，因此对全球情况的了解较少。准确的GIC预测所需的缺失环节是链的核心部分的物理学：了解高动态电离层电流系统如何产生地磁扰动，驱动在基础设施中测量的GIC，从而使现有的太阳风/磁层模型与地面电导率图相结合。我们将使用分布在每个大陆的地面磁力仪(200个站)的数据，来确定八年(2010-2017)期间所有地磁扰动的位置、时间和强度。这些特征将与它们的电离层驱动器有关，该星座由66颗低地球轨道卫星组成，提供这段时间内系统中储存的磁能的连续2分钟快照，并准确地描述电离层电流系统的位置、方向和大小。这种方法的创新之处在于首次将这两个数据集结合在一起，以实现对整个太阳活动高峰期的全球统计分析。我们将主要关注观测到最强烈GIC的高纬度地区(包括北欧、加拿大和美国北部)。我们的工作与空间气象服务提供商(如英国气象局)、能源和铁路行业、监测关键基础设施风险的政府以及未来基础设施规划相关。我们还将研究赤道和中纬度扰动，因为这些扰动有可能扰乱支持主要人口中心的基础设施，而赤道和高纬度事件的结合可能对大陆规模的基础设施(如南美洲)造成极大破坏。这项工作将是利用现有卫星网络和太阳风监测仪相结合，对GIC进行即时预测甚至预测的可行性的探索者。

The Earth's magnetic field sits within the changeable, dynamic environment of the solar wind. The interaction of the two regimes drives rapid reconfigurations of the Earth's field, which induce currents to flow in conductors on the ground. These Geomagnetically Induced Currents (GICs) can be 10s to 100s of Amps, and can cause transformer heating and higher harmonics in power grids, degradation to metal pipelines, and signalling malfunctions on railway systems. The Lloyd's of London 2013 Space Weather report concluded that a once-in-a-Century event 'would cause major disruption to transport, food supplies, emergency and hospital services amongst other things...The absence of such fundamental services could lead to major and widespread social unrest, riots and theft with ramifications for the insurance industry and society in general'. The cost of such an event to the UK has been estimated at £0.9-15.9 billion, and while such huge events are rare, smaller, damaging, events are routinely observed.The key to predicting the location and magnitude of GICs is understanding the chain of causality from the Sun to the Earth's surface, and having instrumentation in key locations to make the measurements required for forecasting. Typical solar wind structures that drive powerful GICs have been identified, and can provide some early warning of extreme dynamics in the Earth's system. The other end of the chain, inducing currents in conductors on the ground due to a variable magnetic field, may be addressed through the application of Faraday's Law, given the conductivity of the local regolith, and the conductivity, length and orientation of the conductor. Typically, this research is funded by individual nations focussing on operational risk to their own critical infrastructure, and therefore the global picture is less well understood. The missing link required for accurate GIC forecasting is the physics of the central part of the chain: understanding how the highly dynamic ionospheric current systems generate the geomagnetic disturbances that drive GICs measured in infrastructure, thus enabling the coupling of existing solar wind/magnetosphere models with ground-based conductivity maps.We will use data from ground-based magnetometers (>200 stations) spread across every continent, to determine the location, timing and intensity of all geomagnetic disturbances over an eight-year period (2010-2017). These signatures will be related to their ionospheric drivers using a constellation of 66 satellites in low-Earth orbit which provide continual 2-minute snapshots of the magnetic energy stored in the system during this time period, and accurately characterise the location, direction and magnitude of the ionospheric current systems. The novelty of this approach is combining these two data sets for the first time to allow a global, statistical analysis over an entire solar maximum period.We will largely focus on high latitude regions (including northern Europe, Canada and the northern United States) where the most intense GICs are observed. Our work is relevant to space weather service providers (such as the UK Met Office), the energy and rail industries, and governments who monitor risk to critical infrastructure, as well as for future infrastructure planning. We will also study equatorial and mid-latitude disturbances, as these have the potential to disrupt infrastructure supporting major population centres, and the combination of equatorial and higher-latitude events could be highly damaging to infrastructure on a continental scale (such as in South America). This work will be a pathfinder for the feasibility of nowcasting, and perhaps even forecasting, of GICs, using acombination of existing satellite networks and solar wind monitors.