Relativistic particle dynamics in the Van Allen Radiation Belts: understanding the science behind Space Weather

As an astrophysical object, the Earth’s magnetosphere would seem to be a rather quiescent body which is in general dominated by relatively slow dynamical processes and small magnetic fields. However, within this environment exists the Van Allen Radiation Belts - torus-shaped regions of relativistic plasma whose origins and behaviour are subjects of fierce scientific debate. Modern society is increasingly reliant on the space-based infrastructure that inhabit this Radiation Belt region to support a wide range of critical services such as Earth observation, defence, telecommunications, GPS navigation, and electronic banking As a result, understanding the existence and variability of this relativistic particle population is of critical importance.

The amount and energy of the plasma in the Radiation Belts is governed by a complex interplay between acceleration, transport and loss processes throughout near-Earth space. Relativistic electron loss is the big unknown in radiation belt physics. Major losses from the system are difficult to quantify, and can occur in a variety of ways, including via interaction with electromagnetic waves, and through large-scale topological changes in the boundary between Earth’s magnetic environment and the solar wind. Under strong solar wind driving this magnetopause boundary can be pushed well inside the geostationary orbit, causing electrons to be lost to the solar wind. At the same time, energetic particles can be scattered into the upper atmosphere where the gas densities are large enough to support collisions. This energetic particle precipitation is also not constant and can vary wildly during active geomagnetic periods, such geomagnetic storms driven by Coronal Mass Ejections. This project will quantify acceleration and losses due to wave-particle interactions and large-scale magnetospheric changes and validate the bedrock of our theoretical understanding of the radiation belts. This project will primarily involve the study of energetic particle data from international satellite missions such as the NASA Van Allen Probes, Mangetospheric MultiScale and THEMIS missions as well as the ESA Cluster mission and NASA SAMPEX missions, and ground-based data from a worldwide network of ionospheric instrumentation and use these results to inform state-of-the-art radiation belt modelling efforts.