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Element Abundances of Solar Energetic Particles and the Photosphere, the Corona, and the Solar Wind

Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742–2431, USA
Atoms 2019, 7(4), 104; https://doi.org/10.3390/atoms7040104
Received: 24 September 2019 / Revised: 16 November 2019 / Accepted: 18 November 2019 / Published: 20 November 2019
(This article belongs to the Special Issue Atomic Physics at the Extreme: The Solar Abundance Problem)
From a turbulent history, the study of the abundances of elements in solar energetic particles (SEPs) has grown into an extensive field that probes the solar corona and physical processes of SEP acceleration and transport. Underlying SEPs are the abundances of the solar corona, which differ from photospheric abundances as a function of the first ionization potentials (FIPs) of the elements. The FIP-dependence of SEPs also differs from that of the solar wind; each has a different magnetic environment, where low-FIP ions and high-FIP neutral atoms rise toward the corona. Two major sources generate SEPs: The small “impulsive” SEP events are associated with magnetic reconnection in solar jets that produce 1000-fold enhancements from H to Pb as a function of mass-to-charge ratio A/Q, and also 1000-fold enhancements in 3He/4He that are produced by resonant wave-particle interactions. In large “gradual” events, SEPs are accelerated at shock waves that are driven out from the Sun by wide, fast coronal mass ejections (CMEs). A/Q dependence of ion transport allows us to estimate Q and hence the source plasma temperature T. Weaker shock waves favor the reacceleration of suprathermal ions accumulated from earlier impulsive SEP events, along with protons from the ambient plasma. In strong shocks, the ambient plasma dominates. Ions from impulsive sources have T ≈ 3 MK; those from ambient coronal plasma have T = 1 – 2 MK. These FIP- and A/Q-dependences explore complex new interactions in the corona and in SEP sources. View Full-Text
Keywords: solar energetic particles; element abundances; magnetic reconnection; shock acceleration; solar wind solar energetic particles; element abundances; magnetic reconnection; shock acceleration; solar wind
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Reames, D.V. Element Abundances of Solar Energetic Particles and the Photosphere, the Corona, and the Solar Wind. Atoms 2019, 7, 104.

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