Fifty Years of 3He-rich Events. (arXiv:2110.06251v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Reames_D/0/1/0/all/0/1">Donald V. Reames</a>
The early 1970s saw a new and surprising feature in the composition of solar
energetic particles (SEPs), resonant enhancements up to 10,000-fold in the
ratio 3He/4He that could even make 3He dominant over H in rare events. It was
soon learned that these events also had enhancements in the abundances of
heavier elements, such as a factor of ~10 enhancements in Fe/O, which was later
seen to be part of a smooth increase in enhancements vs. mass-to-charge ratio
A/Q from H to Pb, rising by a factor of ~1000. These events were also
associated with streaming 10 – 100 keV electrons that produce type III radio
bursts. In recent years we have found these “impulsive” SEP events to be
accelerated in islands of magnetic reconnection from plasma temperatures of 2 –
3 MK on open field lines in solar jets. Similar reconnection on closed loops
traps the energy of the particles to produce hot (>10 MK), bright flares.
Sometimes impulsive SEP intensities are boosted by shock waves when the jets
launch fast coronal mass ejections. No single theory yet explains both the
sharp resonance in 3He and the smooth increase up to heavier elements; two
processes seem to occur. Sometimes the efficient acceleration even exhausts the
rare 3He in the source region, limiting its fluence.
The early 1970s saw a new and surprising feature in the composition of solar
energetic particles (SEPs), resonant enhancements up to 10,000-fold in the
ratio 3He/4He that could even make 3He dominant over H in rare events. It was
soon learned that these events also had enhancements in the abundances of
heavier elements, such as a factor of ~10 enhancements in Fe/O, which was later
seen to be part of a smooth increase in enhancements vs. mass-to-charge ratio
A/Q from H to Pb, rising by a factor of ~1000. These events were also
associated with streaming 10 – 100 keV electrons that produce type III radio
bursts. In recent years we have found these “impulsive” SEP events to be
accelerated in islands of magnetic reconnection from plasma temperatures of 2 –
3 MK on open field lines in solar jets. Similar reconnection on closed loops
traps the energy of the particles to produce hot (>10 MK), bright flares.
Sometimes impulsive SEP intensities are boosted by shock waves when the jets
launch fast coronal mass ejections. No single theory yet explains both the
sharp resonance in 3He and the smooth increase up to heavier elements; two
processes seem to occur. Sometimes the efficient acceleration even exhausts the
rare 3He in the source region, limiting its fluence.
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