A High-Order Model of the Earth's External and Induced Magnetic Field

几个世纪以来，人们一直使用磁罗盘来指引他们的道路和探索新的领域。这使得科学家们开始了他们自己关于地磁的发现之旅，并发现了作为现代技术——电话、电视、电脑等——核心的电磁学。现在，在全球定位系统的时代，你可能会认为指南针已经过时了，但地球磁场的引导对于勘探地下石油和矿产（全球定位系统无法到达的地方）以及作为飞机的安全备份等仍然至关重要。而且，具有讽刺意味的是，GPS受到地球磁场引起的自然灾害的影响。因此，对地磁的科学研究在很多方面仍然很重要，以至于2012年欧洲航天局（European Space Agency）将发射一项名为Swarm的任务，其中三颗卫星将围绕地球运行，以前所未有的细节调查地球磁场。这些测量结果将用于改进地磁场的数学模型，为各种应用提供标准参考。一个目标领域是更好地理解和描述由上层大气和空间中流动的电流引起的相对快速和复杂的磁波动，这种波动最终是由太阳上发生的扰动所驱动的，这种扰动以11年的太阳周期为周期。这种所谓的外磁场还会诱导洋流在海洋和地球表面下流动，从而产生额外的磁场波动。外部磁场和感应磁场共同限制了地磁场模型的准确性，因此，在磁场波动较大的地点和时间，例如在极地地区和可能每月发生一次并持续数天的所谓磁暴期间，这些模型对测量和导航毫无帮助。EIMF还对大型导电系统造成自然危害，如电网停电、输油管道腐蚀，甚至铁路信号幻象。在这个项目中，我们将使用在世界各地300多个不同地点进行的太阳周期测量值来研究EIMF，这些测量值最近首次由一个名为SuperMAG的国际项目收集。我们的想法是借用气象学家通常用于研究天气和气候的数学技术来确定EIMF的自然周期和模式。结合Swarm任务，由此产生的对EIMF“天气”和“气候”的新描述和理解应该有助于改进下一代地球磁场的计算机模型。它也可以作为评估和预测英国国家电网因EIMF的极端波动而导致停电风险的依据。

For centuries people have used magnetic compasses to guide them on their way and explore new territories. This has led scientists to embark on their own journeys of discovery about Earth's magnetism, and to the discovery of electromagnetism that is at the heart of modern technology - phones, TVs, computers, etc. Now, in the age of GPS, you might think that compasses are obsolete, but guidance by the Earth's magnetic field is still vital to explore for oil and minerals below ground (where GPS can't reach) and as a safety backup for planes, etc. And, ironically, GPS is affected by natural hazards caused by the Earth's magnetic field.So the scientific study of Earth's magnetism continues to be important in many ways, so much so that in 2012 the European Space Agency will launch a mission called Swarm in which three satellites will orbit the Earth to survey its magnetic field in unprecedented detail. These measurements will be used to improve mathematical models of the geomagnetic field that provide a standard reference for various applications. One target area is a better understanding and description of the relatively rapid and complex magnetic fluctuations caused by electrical currents flowing in the upper atmosphere and in Space, ultimately driven by disturbances happening on the Sun that wax and wane with an 11-year solar cycle. This so-called external magnetic field also induces currents to flow in oceans and under the Earth's surface which in turn creates additional magnetic fluctuations.Together, the external and induced magnetic field (EIMF) limits the accuracy of geomagnetic field models such that they aren't useful for surveys and navigation at places and times when the EIMF fluctuations are large, such as in the polar regions and during so-called magnetic storms that may happen once a month and last several days. The EIMF also creates a natural hazard for large-scale electrically conducting systems such as power outages in electricity grids, corrosion in oil pipelines, and even phantom railway signals.In this project we will study the EIMF using a solar cycle's worth of measurements made at over 300 different locations around the world, recently collected together for the first time by an international project called SuperMAG. Our idea is to borrow mathematical techniques usually used by meteorologists for studying the weather and climate to identify the natural cycles and patterns of the EIMF. In conjunction with the Swarm mission, the resulting new descriptions and understanding of the EIMF "weather" and "climate" should help to improve the next generation of computer models of Earth's magnetic field. It can also be used to as a basis to assess and predict the risk of power outages in UK's National Grid caused by extreme EIMF fluctuations.