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

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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.