Abstract
Magnetospheric chorus waves play a dominant role in accelerating high energy electrons and in precipitating energetic electrons in the radiation belts. Numerous simulation techniques have been employed to investigate chorus wave propagation, among which ray tracing theory has been the most commonly utilized method.
In a smooth magnetosphere, ray tracing theory predicts a linear increase in wave normal angle with latitude for chorus waves generated at the equator. However, in the presence of magnetospheric ducts observations show the wave normal angles are lower on average at high latitudes, and the waves exhibit parallel propagation. Magnetospheric ducts can effectively guide whistler-mode waves to high latitudes and enforce parallel propagation. In this study, we implement a finite difference time domain (FDTD) model for a more realistic representation of wave propagation, alongside a ray tracing model for qualitative insights, to simulate whistler-mode wave propagation in both homogeneous and inhomogeneous cold plasma within a realistic dipole geomagnetic field.
Both the FDTD and ray tracing model produce the linear increase in wave normal angle with latitude for non-ducted wave propagation in a smooth magnetosphere. However, when ducts are introduced, the waves show a combination of guiding and refraction in the full wave model that is considerably more complex. The ducts also enforce strong spatial modulation, guiding of waves inside the duct region and creating a shadow region due to geomagnetic curvature. These phenomena are consistent with observation from the Van Allen Probes spacecraft.