Coronal Disturbances and the Early Evolution of SEP Events

Many solar energetic particle (SEP) events have been observed at widely separate heliographic longitudes during solar cycle 24, on the basis of data taken around the Sun-Earth line and at twin STEREO spacecraft. Earlier studies of this phenomenon emphasized the possible role of coronal disturbances in the form of EUV waves in the acceleration and transport of the particles in the low corona. However, more recent studies tend to downplay EUV waves because they are first of all not seen to propagate to the footpoints of the magnetic field lines that connect to the observer. It is therefore important to model coronal disturbances in 3D by combining EUV images and coronagraph data, instead of relying only on EUV waves, which are often considered to be the low-altitude manifestations of shock waves driven by coronal mass ejections (CMEs). We note a wide variety of spatial and temporal characteristics of SEP events in their early evolution even though the associated coronal disturbances appear to be similar. In extreme cases, we see no SEPs even from strong eruptions that occur around well-connected longitudes, accompanying type II bursts and EUV waves and resulting in fast CMEs. We give a correlative study of a large number of solar eruptions that produced fast CMEs/type II bursts/EUV waves with or without SEP events and discuss the properties of the eruptions that could influence particle acceleration and transport. We also discuss the caveat of using standard magnetic field extrapolation and field line tracing in the studies of the spatial and temporal behaviors of SEP events.