TESTING TRANSPORT THEORIES WITH SOLAR ENERGETIC PARTICLES

The detailed modeling of solar particle events offers the possibility of deriving coefficients describing the propagation of energetic particles in the inner heliosphere such as scattering mean free paths and thus to test the validity of different theories for the interaction of the particles with magnetic field fluctuations. In addition, information about the three-dimensional structure and the dynamical properties of the fluctuations can be obtained and compared with results from direct magnetic field observations. We apply different methods to numerically solve the focused transport equation for pitch angle diffusion coefficients calculated from standard and dynamical quasi-linear theory, and investigate the resulting pitch angle distributions for 100 keV electrons and for MeV protons. We find that pitch angle distributions predicted for electrons from a model comprising dynamical quasi-linear theory and the assumption that the fluctuations are composed of a 20% slab and an 80% two-dimensional component differ significantly from those predicted for protons. A comparison with particle observations from the solar event of 2000 February 18 reveals that these predictions are also in strong disagreement with the observed electron pitch angle distributions. Our findings indicate that the above model, inspite of its recent success in making quantitatively correct predictions for the particle's scattering mean free path parallel to the average magnetic field from observations of solar wind turbulence, is still not complete.