Identifying the effect of coronal shocks on the longitudinal extent of >25 MeV proton events.

Recent studies with stereoscopic observations by STEREO and SOHO have indicated that coronal shocks are sufficiently strong and broad to accelerate high energetic particles in a wide longitudinal range in the heliosphere. Here, we evaluate the role of coronal shocks on the longitudinal extent of >25 MeV proton events. To that end, we predict whether an in-situ observer at 1 AU will detect (or not detect) a significant increase in the intensity of protons, solely using imaging observations of coronal shocks obtained from the COR2s on STEREOs and C2/C3 on SOHO. Our prediction scheme allows us to determine if coronal shocks play a major or minor role in accelerating high energy particles. We have selected 157 events where the CMEs and shock waves responsible for the proton events are identified, from the Richardson et al. (2014) list. We use the ellipsoid model to estimate the three-dimensional direction and angular extent of shocks observed from multiple viewing perspectives. A nominal Parker spiral field line is used for the magnetic connection between the Sun and each in-situ observer (STEREO-A, -B, and SOHO). We assume the scatter-free condition; namely, particles are strictly propagating along magnetic field lines. The prediction is made for each in-situ observer by determining whether the shock is wide enough to intercept the given nominal Parker spiral field line. The predictions made solely by the shock angular extent are in good agreement with actual energetic particle observations for both associated and not associated with proton events. The accuracy rates for the predictions of detection and non-detection of the proton intensity increase are 74% and 83%, respectively, with the accuracy rate of 80% for all cases. Based on the accuracy rates, we conclude that the coronal shocks play a major role in accelerating high energy protons among others.