Modelling the impact of geomagnetically induced currents on UK railways

空间天气包括一系列最终由太阳活动驱动的环境现象。直接向地球发射的太阳能和物质会在地球表面产生电磁干扰。在正常的太阳活动水平下，空间天气的影响微乎其微。然而，太阳活动的自然变化可能会导致严重(通常是十年一次)和极端(几百年一次)的空间天气，在此期间，这些现象的强度可能会增加许多个数量级。在空间天气风暴期间，快速、高幅度的地磁变化在地球的导电地下产生地电场。不同区域之间地电场的不平衡导致地磁感应电流(GIC)在接地的导体结构中流动。因此，空间天气对支撑我们社会和经济的一些关键硬件、基础设施和服务构成了环境风险。空间天气的风险被列入英国民用应急国家风险登记册。铁路是首批受到空间天气影响的现代基础设施之一，因为它们依赖电报技术来发送信号。1871年出版的《自然》杂志报道，由于地磁风暴的干扰，埃克塞特的火车延误了，天文学家沃尔特·蒙德报告说，在1882年11月的地磁风暴期间，铁路信号设备受到了干扰。1921年5月的风暴对纽约州的铁路运营产生了如此广泛的影响，以至于被称为“纽约铁路风暴”。现代信令已经脱离了基于电报的系统，但当代技术也不能幸免于GIC。轨道电路是用于检测某段铁路线上的列车并防止其他列车进入该段的主要系统之一。它们依赖于一种电路，在这种电路中，列车的车轴关闭了铁轨之间的电流回路，但容易受到铁轨中感应的杂散电流的干扰。最近有证据表明，这类信号系统中的异常情况与瑞典和俄罗斯铁路运营中发生的地磁风暴条件不谋而合。信号系统报告在没有列车的扇区出现假阻塞(右侧故障)，对异常数据的统计分析表明，这些异常的发生和持续时间在强地磁风暴期间发生的可能性高出5-7倍。这些影响可能不仅限于高纬度的基础设施。事实上，通过平行研究了解对输电网构成的风险，人们越来越意识到GIC风险是对中低纬地区的威胁，因为严重和极端的空间天气事件将地磁扰动推向赤道。然而，铁路系统面临的风险仍不确定。例如，目前尚不清楚GIC在这类系统中导致错误侧(即安全关键)故障的可能性有多大，我们也尚未经历合理的最坏情况对现代铁路系统的影响，例如1859年被称为“卡林顿事件”的超级风暴。在这个项目中，我们将进行实验和建模工作，首次全面探讨空间天气对铁路信号的风险。这将包括使我们能够评估在任何观测到的地磁条件下施加在英国地面上的地电场的测量。我们还将建立英国最先进的铁路网计算机模型，使我们能够评估(I)地磁环境因素和(Ii)与信号误操作有关的网络特征。这一结果将对其他空间气象研究人员、铁路运营商和政策制定者具有重要意义。

Space weather encompasses a range of environmental phenomena, ultimately driven by solar activity. The emission of solar energy and material directed towards Earth can drive electromagnetic disturbances at the planet's surface. Under normal levels of solar activity, the impact of space weather is minimal. However, natural variations in solar activity can drive periods of severe (typically on decadal timescales) and extreme (once every few hundred years) space weather during which the intensity of these phenomena can increase by many orders of magnitude. Rapid, high-amplitude geomagnetic variations during space weather storms induce geoelectric fields in the electrically conductive subsurface of the Earth. The imbalance in the geoelectric field between different regions causes Geomagnetically Induced Currents (GIC) to flow in conducting structures grounded to the Earth. Space weather thus presents an environmental risk to some of the critical hardware, infrastructure and services underpinning our society and economy. The risk of space weather is recognised by its inclusion in the UK National Risk Register for Civil Emergencies.Railways were among the first modern infrastructure to be impacted by space weather due their reliance on telegraph technology for signalling purposes. It was reported in an 1871 issue of Nature that the interference due to a geomagnetic storm delayed trains in Exeter, and the astronomer Walter Maunder, reported interference with railway signalling equipment during the geomagnetic storm of November 1882. The storm of May 1921 had such an extensive impact on the operation on railway operations in New York State that it has been dubbed the "New York Railroad storm". Modern signalling has moved away from telegraph-based systems, but contemporary technologies are not immune from GIC. Track circuits are one of the main systems used to detect trains along a section of railway line and prevent other train from entering that section. They rely upon an electrical circuit in which the train's axles close a current loop between the rails but are vulnerable to interference from stray currents induced in the rails. There is recent evidence of anomalies in such signalling systems that coincided with the occurrence of geomagnetic-storm conditions in Swedish and Russian rail operations. Signalling systems reported false blockages (right-side failure) in sectors where no trains were present and statistical analyses of anomaly data indicate that the occurrence and duration of these anomalies showed a 5-7 times higher probability of occurrence during strong geomagnetic storms. These impacts may not be limited to infrastructure at high latitudes. Indeed, there is an increasing awareness from parallel research to understand the risks posed to electricity transmission grids that the GIC risk is a threat to mid- and low-latitude regions since severe and extreme space weather events push geomagnetic disturbance equatorwards. However, the risks to rail systems remain uncertain. For example, it is unclear how likely GIC are to induce wrong-side (i.e. safety critical) failures in such systems and we have yet to experience the impact of a reasonable worst-case scenario, such as the 1859 superstorm known as the "Carrington Event", on modern rail systems.In this project, we shall undertake experimental and modelling work to comprehensively explore the space weather risk to rail signalling for the first time. This will include measurements that will enable us to assess the geoelectric field imposed upon the ground in the UK under any observed geomagnetic conditions. We will also build a state-of-the-art computer model of the rail network in the UK that will enable us to evaluate (i) the geomagnetic environmental factors and (ii) the characteristics of the network relevant to signalling misoperations. The results will be important for other space weather researchers, rail operators and policy makers.