Fast and Wide CMEs without Observed >20 MeV Protons

Abstract

Abstract Statistical studies have found a close association between large solar energetic particle (SEP) events and fast and wide coronal mass ejections (CMEs). However, not all fast and wide CMEs have an associated SEP event. From the Coordinated Data Analysis Web catalog of CMEs observed by the Solar and Heliospheric Observatory (SOHO) between 2009 January 1 and 2014 September 30, we select fast (plane-of-sky speed >1000 km s−1) and wide (plane-of-sky angular width >120°) CMEs and determine whether >20 MeV protons were detected by either SOHO or the Solar TErrestrial RElations Observatory (STEREO-A or STEREO-B). Among the 123 selected CMEs, only 11 did not produce a >20 MeV proton intensity increase at any of the three spacecraft. We use multispacecraft coronagraph observations to reevaluate the speeds and widths of the CMEs. The 11 CMEs without observed >20 MeV protons tend to be in the narrow and slow end of the distribution of the selected CMEs. We consider several factors that might play a role in the nonobservation of high-energy particles in these events, including (1) the ambiguous determination of the CME parameters, (2) the inefficiency of the particle sources to produce >20 MeV protons, (3) the lack of magnetic connection between particle sources and any spacecraft, and (4) the lack of particles accelerated and released during the parent solar eruptions. Whereas the extent of the high Mach number regions formed in front of the CME is limited, the characteristic that seems to distinguish those fast and wide CMEs that lack observed >20 MeV protons is a deficit in the release of particles during the solar eruptions.