Browsing by Author "Takala, Saara"

Ultra-low frequency (ULF) waves in the Pc4-Pc5, 2 – 25 mHz range have been observed to accelerate trapped 1 – 10 MeV electrons in the Earth’s radiation belts. This acceleration can lead to particle losses and injections that occur on timescales comparable to the particle drift periods. Current models rely on diffusion equations written in terms of Fokker-Planck equations and are not suitable for describing fast temporal variations in the distribution function. This thesis is a study of fast transport of equatorially trapped electrons in the radiation belts. We look at solutions for the time evolution of the linear part of the perturbed distribution function using both analytical and numerical methods. Based on this work we build a simple model of fast transport in the radiation belts using a spectral PDE framework called Dedalus. The resulting program is a computationally inexpensive, simple approach to modelling drift-periodic signatures on fast timescales. In this study we investigate the behavior of the distribution function in three systems: a simple system without a wave term, and systems with a single non-resonant and resonant ULF wave. The wave solutions are evaluated with magnetic field perturbations of different magnitudes. The Earth’s magnetic field is modelled with the Mead field. The numerical solution of the perturbed differential equation is studied for relativistic equatorially trapped electrons. Phase-mixing is found to happen regardless of field fluctuations or resonance. The non-resonant wave solution shows time-delayed, spatially localized structures in the equatorial plane forming in the presence of large magnetic field fluctuations. These transients are also seen in the analytical solution and provide a new theoretical explanation for the ubiquitous observation of drift echoes in the inner and outer radiation belts of the Earth (Li et al., 2024).