Estimating and Validating Diffusion Coefficients with Particle Data

Abstract:

Most radiation belt simulations today require diffusion coefficients, either for pitch angle, energy, or radial diffusion. These coefficients are primarily derived from observations of plasma and magnetohydrodynamic waves. Multiple studies have shown success reproducing local and global topography and dynamics of the radiation belts based on such coefficients. However, due to substantial differences in the choices of physical mechanisms to include in such studies, it remains unclear which physical mechanisms are actually necessary or dominant. Some of this uncertainty arises from uncertainty in the diffusion coefficients. We present recent studies in which we have used in situ particle data to derive or infer the diffusion coefficients. These approaches provide a check on the wave-derived coefficients. We describe eigenmode analysis, spatial quadrature, and drift phase structure analysis as different methods of deriving and constraining the diffusion coefficients.