"Energetic particles from impulsive solar flares,"
ApJS 73, 235 (1990).
Click on the image above for a larger .gif version.
The work of Don Reames has been fundamental in distinguishing "impulsive" solar particle (SEP) events (SPEs) from "gradual" ones, with the latter strongly identified with the coronal and interplanetary shock waves known (e.g., via geomagnetic effects) to be associated with flares and coronal mass ejections. The shock mechanisms, whether the whole story or not, have a well-developed theoretical literature. This does not seem to be the case for the particle acceleration associated with impulsive SEPs, and this cartoon was a pioneering effort to understand the configuration in the low corona. Other configurations (e.g., the Heyvaerts et al. reconnection model), may have more followers now, but the case remains open (as do the pesky and ill-understood flux tubes that guide the particles from the lowest corona into the distant heliosphere).
Here the idea, due originally to Sprangle and Vlahos, is that resonant electron cyclotron waves can couple the flare volume with the open flux tube. To the Archivist's mind, this seems a lot more attractive than an MHD reconnection model, which would involve singular surfaces and not actual volumes - we know observationally that the open flux tubes expand broadly into space, and do not behave like sheets.
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