Coronal Waves and Solar Energetic Particle Events Observed at Widely Separate Locations

Abstract:

During solar cycle 24, thanks largely to the Solar Terrestrial Relations Observatory (STEREO), many solar energetic particle (SEP) events have been observed at widely separate locations in the heliosphere, even including impulsive events that are usually assumed to reflect localized acceleration and injection. It is found that many of these wide SEP events accompany coronal waves that typically appear in extreme-ultraviolet (EUV) images. The EUV wave phenomenon has been observed much more closely than before by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory that continuously produces full-disk EUV images with unprecedentedly fast cadence and high sensitivity in multiple wavelength bands covering a broad temperature range. This is complemented by the EUV Imager on STEREO that traces the wave front into regions inaccessible from Earth. Several authors have attempted to explain wide SEP events in terms of EUV waves, especially comparing the SEP release times with how and when the EUV wave fronts traverse the magnetic footprints of the locations of SEPs. They have come to mixed results. The primary reason for the mixed results may be that they tend to overlook or underestimate the uncertainties inherent in the works. For example, how well do we model magnetic field connection in the corona and heliosphere? Do we adequately take into account the evolving solar wind conditions? Here we study a number of SEP events with various angular spreads in comparison with newly analyzed EUV waves. We discuss the importance of including the above-mentioned uncertainties as well as understanding EUV waves as part of the 3d propagation of CME-driven shock waves into the coronagraph fields of view. Without these approaches, it may remain ambiguous how much of the angular spread of SEP events is attributable to coronal shock waves.