LESIA - Observatoire de Paris

History of Research on Solar Energetic Particle Events : The Evolving Paradigm

mercredi 15 juin 2016, par E.W. Cliver (National Solar Observatory, Boulder, CO, USA)

Mercredi 22 juin 2016 à 11h00 , Lieu : Salle de réunion du bâtiment 14

I review the evolution of research on the acceleration of solar energetic particles (SEPs) – beginning with Forbush’s observation of two ground level events in 1942, through the first suggestion of the two-phase (flare and shock) picture of Wild, Smerd, and Weiss (1963), on up to the present day. During my own time working in the field, I have seen SEP studies go from a pre-paradigmatic state to one with a well-defined conceptual framework. Highlights include the linkage of CMEs and shocks to SEP events by Kahler, Cane and others, the seminal paper by Reames, Lin, and von Rosenvinge (1985) that linked 3He-rich events with small electron events, and the recognition of the importance of seed particles and shock geometry by Tylka et al. (2005). The notion that large high-energy (> 25 MeV/nuc) “gradual” SEP events originate primarily at CME-driven shocks was challenged by the observation of large SEP events by ACE in 1997-1998 that had “impulsive” event characteristics and has been questioned again more recently in studies by Dierckxsens et al. (2015), Trottet et al. (2015), and Grechnev et al. (2015). Of these, I focus on the Grechnev et al. study that considered >100 MeV protons. The presence of two particle acceleration mechanisms at the Sun (flare and shock) and the oscillation in emphasis between these mechanisms remain a spur for progress in this field.

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