Multi-Spacecraft Observations of Unexpectedly Wide SEP Spreads in Solar Cycle 24

Abstract:

Since the launch of the STEREO mission in 2006 the two spacecraft build an unprecedented observational platform to investigate solar energetic particle (SEP) events at 1AU. The growing longitudinal separation of the spacecraft improved the ability to investigate the longitudinal distribution of SEP events and to unambiguously detect wide-spread events. Several of those events showing longitudinal SEP distributions of up to all around the Sun have been observed. The strongly varying characteristics of those events suggest that there must be various mechanisms which contribute to the wide angular particle spreads. On the one hand strong perpendicular diffusion is favored to explain those wide SEP spreads. In this scenario we expect isotropic fluxes at far separated observers. However, other events show significant anisotropies over broad longitudinal ranges which requires extended injection regions close to the Sun. Several processes are under discussion which would provide those exteded injections, e.g. coronal and interplanetary shocks, coronal transport processes, and EIT waves. We will discuss case studies as well as statistical investigations of wide-spread SEP observations in terms of the most important drivers of these wide particle distributions.