Determining the processes behind near-steady radiation belt losses

Plasma particles (ions and electrons) trapped on closed field-lines in Earth's magnetosphere can be energised to MeV energies by a range of wave-particle interactions. These particles make up the Van Allen Radiation Belts - two taurus-like regions of high energy particles encircling the Earth from approximately geosynchronous orbit inwards. The number of high energy particles in the radiation belts is a balance between particles being accelerated to high energies, e.g. by diffusion or interactions with whistler-mode waves, and particles being lost from the region, e.g. by outward diffusion, loss through the magnetopause and loss to the atmosphere. Recent studies of the number of particles in the radiation belts have shown that the proportional change in the number of particles in this region with time is almost constant during periods of low geomagnetic activity, and as such the radiation belts are constantly leaking particles. Understanding these loss processes is important in order to understand the physics that underpins the radiation belts, which is crucial in order to correctly model this and predict the impact of space weather, and also to provide information as to the rates of precipitation into the upper atmosphere, where energetic charged particles can alter high-altitude atmospheric chemistry.

In this project, the student will examine where this loss is most dominant and how this relates to some initial conditions within the radiation belts, whether existing wave-particle interaction theory can explain these loss rates, and whether these loss rates also hold during times when the radiation belts are being enhanced. This project will primarily involve using data from the NASA Van Allen Probes, although further data sources include the LANL and GOES geosynchronous satellites, the low-Earth orbiting SAMPEX and POES spacecraft and ground-based STP data.