Kinetic energy variations within drift orbits: a study in UBK space

Three dimensional radiation belt models like the BAS radiation belt model and the VERB code assume that trapped electrons within the model space remain at a fixed kinetic energy in the absence of wave-particle interactions. However, it is also accepted that at lower energies convection due to the electric field can significantly alter the trajectories and kinetic energy of trapped electrons. Using coordinates of electric potential, magnetic field strength, and the modified second invariant (UBK), we present a mathematically simple approach to describing the full phase space of possible particle trajectories within given magnetic and electric field models. We further demonstrate that it can be used to determine the change in kinetic energy around any particle orbit, and that changing trajectories and kinetic energies can have a significant effect on satellite measurements of energy spectra.