Solar Physics

Helium-Rich Flares

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Science  26 Jan 2001:
Vol. 291, Issue 5504, pp. 555
DOI: 10.1126/science.291.5504.555e

Solar flares spew hot plasma at Earth, and this plasma interacts with the magnetosphere, ionosphere and atmosphere. Conspicuous manifestations of this interaction are space weather and aurorae.

Mason et al. used the Advanced Composition Explorer spacecraft to measure the composition of some of the lowest energy particles in a flare. They measured extremely high 3He/4He in some flares and slight enrichments of Fe ions in all flares. The helium ratio is much higher than the average solar corona helium ratio, consistent with previous measurements at different energy ranges. The enrichment in 3He in some flares may be related to a special acceleration mechanism that depends on the small charge-to-mass ratio of the helium isotope. These measurements indicate that a 3He-enriched region combines with an iron-rich region and that the mixture is then accelerated in a solar flare in a two-stage formation process. — LR

Astrophys. J.545, L157 (2000).

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