3He-rich solar flares

Abstract

The formation of the observed solar cosmic ray (SCR) composition remains an open question.It has become particularly acute after the discovery of 3He-rich events. The 3He/4He abundance ratio revealed in such events exceeds substantially (up to four orders of magnitude) that in the solar atmosphere.The data available on the 3He-rich events are discussed and a list of all such events known up to date is presented. Most of the 3He-rich SCR events can be associated with the corresponding optical flares on the Sun, with X-ray and radiobursts.An analysis of the models of 3He enrichement proposed up to now shows that only preferential 3He heating by plasma mechanisms can provide the observed high enrichment levels (3He/4He ~ 1).A model involving preferential heating of 3He by induced scattering on ions of the ion acoustic waves generated by flare associated electrons in the solar atmosphere is considered in detail. This model can account for the major properties of the 3He-rich flares.Observational implications of the 3He-rich solar flare model are analyzed; the predictions of the theory are compared with the experimental data available, and promising avenues of further relevant experimental and theoretical research are considered.

Particle acceleration in solar flares

“…The most dramatic departure of a solar energetic particle abundance from its photospheric value is that of 3He [Garrard, Stone, and Vogt, 1973]. Here very large enhancements are observed in the 3He/4He ratio above its likely photospheric value [see Kocharov and Kocharov, 1984 for review]. These enhancements are probably caused by resonant heating of 3He in the ambient atmosphere which could lead to the preferential accelerations of aHe [Fisk, 1978;Kocharov and Kocharov, 1978].…”

3He-rich Solar Energetic Particles in Helical Jets on the Sun

“…The most striking feature of particle acceleration in solar flares is the enormous enrichment of the rare isotope 3 He by factors up to 10 4 above coronal or solar wind values (Kocharov & Kocharov 1984). This 3 He-rich solar energetic particle (SEP) population is further characterized by enrichments in heavy (Ne-Fe) and ultra-heavy (mass>70) ions by a factor of ∼2-10 and >100, respectively, independent of the amount of 3 He enhancement (Mason et al 1986(Mason et al , 2004Reames et al 1994).…”

Abundances of Heavy and Ultraheavy Ions in3He‐rich Solar Flares

“…In addition, compared to large-SEP events, 3 He-rich events are generally short lasting, are associated with type III electron bursts, and exhibit significantly higher heavy-ion charge states. Many theoretical studies have been undertaken to model these particle events, generally making use of the unique charge-to-mass (Q/M ) ratio of 3 He and the difference between the Q/M ratio of heavier ions and that of oxygen expected at coronal temperatures (e.g., see reviews by Kocharov & Kocharov 1984;Miller 1998;Reames 1999). This research remains quite active, with a number of possible mechanisms still being studied.…”