Evidence for Remnant Flare Suprathermals in the Source Population of Solar Energetic Particles in the 2000 Bastille Day Event

Abstract

The energy spectra of Fe in the very large solar energetic particle (SEP) event of 2000 July 14 are strikingly different from those of lighter species. We show that this difference can be explained by shock acceleration from a two-component source population, comprising solar wind suprathermals and a small (∼5%) admixture of remnant flare particles, as previously proposed to explain enhanced 3 He/ 4 He in some gradual SEP events. Flare remnants can also account for several previously unexplained features of high-energy solar heavy ions as well as important aspects of SEP event-to-event variability. These results offer a new perspective on the enduring controversy over the relative roles of flares and coronal mass ejections (CMEs) in producing SEPs. Flare activity clearly makes a unique and critical contribution to the source population. But the predominate accelerator in large gradual SEP events is the CME-driven shock, and many spectral, compositional, and charge state characteristics of highenergy heavy ions can be understood without invoking other acceleration mechanisms.

Observations of Energetic Storm Particles: An Overview

“…The authors observed more quasiperpendicular shocks than quasi-parallel ones, but found the larger particle increases were associated with quasiparallel shocks. This was consistent with the observations of van Nes et al [1984] for shocks with 30° < θ Bn < 60°a nd suggested that diffusive shock acceleration was more efficient at accelerating 35-56 keV protons than shock-drift acceleration.…”

Acceleration and Enrichment of3He in Impulsive Solar Flares by Electron Firehose Waves

“…This suggests that different mechanisms are responsible for the acceleration of the two species. Gradual flares usually have large energetic proton fluxes and small 4 He/H and do not show large 3 He/ 4 He or Fe/C enhancements in the energetic particles, although approximately 5% admixture of suprathermal remnant particles from impulsive flares has been observed in gradual events by Tylka et al (2001). The standard interpretation for these observations is that the energetic particles in impulsive events originate in the energy release region on the Sun while the energetic particles in gradual events are accelerated via shocks, either coronal or interplanetary (Lin 1987;Luhn et al 1987).…”

Suprathermal Particle Populations in the Solar Wind and Corona

“…One plausible scenario is that suprathermal ions (e.g., 3 He) remnant from impulsive events (at the flare site) may be a source population available for further acceleration by interplanetary shocks that accompany large SEP events, thereby leading to the 3 He enhancements in a significant fraction of large SEP events. There is also evidence of heavier suprathermal ions, e.g., Fe, remnant from flares and present in the source population of LSEP events (Tylka et al, 2001). …”