Modeling the 2012 May 17 Solar Energetic Particle Event Using the AWSoM and iPATH Models

We model the 2012 May 17 solar energetic particle event by combining the AWSoM and iPATH codes. Using this combined approach, we investigate particle acceleration when the parent coronal mass ejection (CME) is still close to the Sun. We have obtained reasonable agreements between our simulation and observations made by multiple spacecraft. We follow the three-dimensional CME and the CME-driven shock from their initiation using the AWSoM code for a period of 3 hours when the shock is below similar to 20 R ( s ). Above 20 R ( s ), iPATH2D is used to follow the CME-driven shock. The plasma properties from the AWSoM code are fed into the iPATH model, where particle acceleration at the shock front is modelled and the instantaneous energetic particle spectra are obtained. The subsequent transport of these energetic particles in the solar wind is followed using the iPATH model. We obtain both the instantaneous particle spectra and particle fluence at 1 au, and we then compare them with observations. To account for uncertainties of magnetic field connectivity from 1 au to the shock, as well as uncertainties of the shock profiles, our model's results are obtained as an ensemble average where, instead of considering Earth as a single point location, we consider multiple locations within 10 degrees in longitude and latitude from Earth. The effect of this model uncertainty mimics that of the field line meandering, as suggested by Bian & Li, but is of different origin. We suggest that a trustworthy solar energetic particle forecast should be made in an ensemble average approach.