Unveiling the timescales and intensities of solar-terrestrial interactions using novel datasets and techniques

我的研究将量化地球对太阳风的反应，太阳风是一种来自太阳并携带磁场的连续粒子流。包含地球自身磁场的空间区域被称为磁层，而太阳风中的磁场和粒子与磁层的边缘相互作用，这被称为磁层顶。发生在磁层顶的相互作用通过沿地球磁场流动的电流传递到地球大气层的电离层（海拔100千米以上），这种电流被称为伯克兰电流。这些电流在磁层顶和磁层内的触发下流动，反过来在地球表面造成潜在的危险地磁效应，如损坏卫星或破坏电力和电信基础设施。有两种类型的事件会导致电流增强，从而可能造成潜在的危险影响，它们是地磁风暴和亚风暴。地磁风暴是持续数天的事件，当太阳风驱动磁层顶的大量活动时发生，这反过来又导致大电流在几天内流经系统。亚暴是发生在地球磁层的以小时为时间尺度的事件，它在较短的时间内在地球磁层的特定区域驱动大电流。这两件事之间的对应关系尚不清楚。此外，我们不知道亚暴是从远离地球的地方开始的，并导致向地球移动的影响，还是从离地球很近的地方开始的，并导致远离地球的影响。我将通过使用最初用来观察星系中心的技术来找出这些事情中的哪一个正在发生。了解这些事件，以及了解最大的电流何时流动，对于了解太阳如何扰乱和破坏地球上的基础设施至关重要。另一个重要的研究途径是了解对这些事件的反应有多有效。我们需要知道电离层在不同情况下传导电流的能力，以及电流在北半球和南半球的流动有何不同。在我读博士期间，我发现了伯克兰电流的半球不对称，我将回答的一个问题是（通过检查许多其他数据集以及建模结果）这种半球不对称是从哪里来的。这意味着我可以推断出，在地球表面不同的条件和地点，可以流动的电流是如何不同的，这反过来又能让我们更好地了解这些电流是如何给我们带来问题的。我的研究计划将回答我们对上述主题的关键问题，并将大大提高我们对伯克兰洋流的认识。我将使用来自铱星星座的66个航天器星座来研究洋流，这些航天器在地球表面上方780公里处绕地球轨道运行。用磁力计来测量这些航天器上的磁场，然后用物理方程从这些测量结果中推导出伯克兰电流。我是使用这个数据集的最重要的国际研究人员之一，这个数据集被称为AMPERE，所以我非常适合使用这些数据来回答我们关于伯克兰洋流的问题。

My research will quantify the Earth's reaction to the solar wind, a continuous stream of particles which comes from the Sun and carries magnetic fields with it. The region of space containing Earth's own magnetic field is known as the magnetosphere, and the magnetic fields and particles in the solar wind interact with the edge of the magnetosphere, which is called the magnetopause. The interactions which occur at the magnetopause are communicated to a region of Earth's atmosphere called the ionosphere (at an altitude of just above 100 km) by electrical currents which flow along Earth's magnetic field, called Birkeland currents. These currents flow in reaction to triggers from the magnetopause and within the magnetosphere, in turn causing potentially dangerous geomagnetic effects on the surface of Earth, like damaging satellites or knocking out power and telecoms infrastructure.Two types of event which cause enhanced current flow and thus can cause potentially dangerous effects are geomagnetic storms and substorms. Geomagnetic storms are multi-day events which occur when the solar wind drives a lot of activity at the magnetopause and this in turn causes large currents to flow through the system over a period of days. Substorms are events on hourly timescales which occur in the Earth's magnetosphere and drive large currents in specific areas of Earth's magnetosphere for a shorter period of time. The correspondence between these two events is not well-understood. Furthermore, we do not know whether substorms start far from Earth and cause effects which move towards it, or whether they start close to Earth and cause effects that move away. I will find out which of these things is happening by using techniques originally developed to look at the centres of galaxies. Understanding these events, as well as understanding when the largest currents flow, is vital to understanding how the Sun can disrupt and destroy our infrastructure on Earth.Another important avenue of research is understanding how efficient the response to these events is. We need to know how well the ionosphere can conduct current in different situations as well as how the currents flow differently in the Northern and Southern Hemisphere. During my PhD, I discovered the hemispheric asymmetry in Birkeland current, and one of the questions I will answer (by examining many other datasets alongside modelled results) is where this hemispheric asymmetry comes from. This means I can deduce how the amount of current that can flow is different in different conditions and places on Earth's surface, which will in turn allow us much better insights into how these currents can lead to problems for us on the surface.My research programme will answer key questions we have about the topics above and will significantly advance our knowledge of the Birkeland currents. I will study the currents using a constellation of 66 spacecraft from the Iridium constellation, which orbit the Earth 780 km above the surface. Magnetometers to measure the magnetic field at these spacecraft, and then physical equations are used to derive the Birkeland current from those measurements. I am one of the foremost international researchers using this dataset, which is called AMPERE, and so I am very well-suited to using this data to answer questions we have about the Birkeland currents.