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

TL;DR

This paper reviews the element abundances in solar energetic particles, their relation to solar corona and wind, and how different solar events and shock waves influence SEP composition and acceleration processes.

Contribution

It provides a comprehensive analysis of FIP and A/Q dependencies in SEPs, linking them to solar source conditions and shock wave characteristics, highlighting new insights into SEP acceleration and transport.

Findings

Impulsive SEPs show 1000-fold enhancements in element ratios.

Gradual SEPs are influenced by shock wave strength and source plasma temperature.

FIP and A/Q dependencies reveal complex interactions in the solar corona.

Abstract

From a turbulent history, the study of abundances of elements in solar energetic particles (SEPs) has grown into an extensive field that probes the solar corona and the 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 produced by resonant wave-particle interactions. In large "gradual" events, SEPs are accelerated at shock waves 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 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.