Improving Predictions of Solar Energetic Particle Access at Medium Earth Orbit

Solar energetic particle (SEP) access at medium-Earth orbit is controlled by the structure of the magnetosphere and the rigidity of the particles. Different approaches are taken to describe and predict particle access, from data-derived parameterized models through to test particle simulations in fields from global magnetosphere models. Heuristics for deriving cutoffs from data are convenient, but have generally been derived from low-altitude data. We illustrate cutoff predictions derived using energetic particle data from the Global Positioning System constellation. We then increase the complexity and estimate both the SEP flux spectrum and cutoff rigidities using test particle simulations in different model magnetic field configurations - using both semi-empirical and coupled-physics models. Using the models of varying complexity, with varying targets (flux or cutoff rigidity) we discuss the benefits inherent in each approach and how data and model can be combined to improve both prediction and understanding.