Sarah Bentley - How do modelling choices affect radial diffusion in Earth's radiation belts?

Speaker: Sarah Bentley (University of Northumbria)
Abstract:
Earth’s radiation belts contain high energy, geomagnetically trapped charged particles that are responsible for several space weather hazards. Using conserved quantities associated with the motion of these particles, the radiation belts can be modelled through a basic diffusion equation. On longer timescales, this can be approximated as simply a 1d diffusion equation, representing the changing drift orbit of the electrons as they interact with electromagnetic fields.
Ensemble modelling - running a model many times to represent variations in the underlying physics - is increasingly being adopted by the space physics community to capture the uncertainty, which can be inherent to the system or due to observations or models. But before we can interpret the physics from an ensemble, we must understand what variation arises solely from the modelling method. We investigate the role of fundamental model choices to the evolution of the system, including the details of an initial enhancement, the location of the plasmapause and the outer boundary size and condition.
Our first key result suggests that because the amount of diffusion changes depending on where you are in the modelling domain, the size of the domain affects the way the system evolves. Both the location of the outer boundary, and the numerical condition used there, change the way in which the system evolves, raising questions about operational choices today. The second result we will highlight allows us to quantify how model components contribute to the evolution of the system. Surprisingly, we find that the gradient of the phase space density (PSD) contributes more to the evolution of the system than the diffusion coefficient DLL​. This contradicts our current understanding and has consequences whether correct or incorrect.