http://arxiv.org/abs/1902.03208
Despite its dominance, hydrogen has been largely ignored in studies of the abundance patterns of the chemical elements in gradual solar energetic-particle (SEP) events; those neglected abundances show a surprising new pattern of behavior. Abundance enhancements of elements with 2 <= Z <= 56, relative to coronal abundances, show power-law dependence, versus their average mass-to-charge ratio A/Q, that varies from event to event and with time during events; the ion charge states Q depend upon the source plasma temperature T. For most gradual SEP events, shock waves have accelerated ambient coronal material with T < 2 MK to produce a decreasing power-laws in A/Q; here the proton abundances agree rather well with the power-law fits extrapolated from elements with Z >= 6 at A/Q > 2 down to hydrogen at A/Q = 1. Thus the abundances of the elements with Z >= 6 fairly accurately predict the observed abundance of H, at a similar velocity, in most SEPs. However, for those gradual SEP events where ion enhancements follow positive powers of A/Q, especially those with T > 2 MK where shock waves have reaccelerated residual suprathermal ions from previous impulsive SEP events, pro-ton abundances commonly exceed the extrapolated expectation, usually by a factor of order 10. This is a new and unexpected pattern of behavior that is unique to the abun-dances of protons. This proton behavior is a signature that can help distinguish the presence or absence of shock acceleration when Fe-rich impulsive material is observed.
D. Reames
Mon, 11 Feb 19
33/51
Comments: 28 pages, 9 figures, submitted to Solar Physics