Impulsive SEP events

Abstract

3He-rich, Fe-rich, and rich in elements with Z > 50, the abundances of solar energetic particles (SEPs) from the small impulsive SEP events stand out as luminaries of our study. Element abundance enhancements increase 1000-fold as the ~3.6 power of the mass-to-charge ratio A/Q from He to Pb, enhanced during acceleration in islands of magnetic reconnection. Their pattern of enhancements suggest a source with C and N fully ionized like He, Ne enhanced more than Mg and Si, and heavy elements following the power-law enhancement versus A/Q with Q at a source temperature of 2.5–3.2 MK. These temperatures are typical of solar active regions from which these impulsive SEPs come. However, in a few events, the element S is greatly enhanced, apparently by the same resonant-wave mechanism that enhances 3He. Which mechanism will dominate? Impulsive SEP events are associated with slow, narrow CMEs, and solar jets where magnetic reconnection on open field lines gives particles direct access to space.