Cosmic Ray Modulation: Improving the Agreement Between Modelling and Observations

We compare the effects of two different models for perpendicular diffusion on the modulation of galactic cosmic ray protons in the heliosphere during solar minimum conditions. These two models correspond to the newly developed non-linear guiding center (NLGC) theory [Matthaeus et al., 2003] and the theory of Bieber and Matthaeus [1997] (known as BAM in several of our earlier publications). A steady-state two-dimensional numerical modulation model is used in this ab initio study, which incorporates a state-of-the-art turbulence model. Factors relevant to an improvement in the agreement between the ab initio modulation model and cosmic ray observations are discussed.