The "FIP Effect" and the Origins of Solar Energetic Particles and of the Solar Wind

TL;DR

This paper investigates how element abundances in solar energetic particles and the solar wind vary with first ionization potential, revealing differences in their origins and the processes that fractionate elements in the solar atmosphere.

Contribution

It provides a detailed analysis of FIP-related abundance patterns in SEPs and solar wind, proposing a model involving Alfvén wave resonance and magnetic structures as the source of these patterns.

Findings

SEP and solar wind abundances reflect the solar corona composition.

FIP crossover points differ between SEPs (~10 eV) and solar wind (~14 eV).

FIP fractionation likely occurs near the top of the chromosphere.

Abstract

We find that the element abundances in solar energetic particles (SEPs) and in the slow solar wind (SSW), relative to those in the photosphere, show different patterns as a function of the first ionization potential (FIP) of the elements. Generally, the SEP and SSW abundances reflect abundance samples of the solar corona, where low-FIP elements, ionized in the chromosphere, are more efficiently conveyed upward to the corona than high-FIP elements that are initially neutral atoms. Abundances of the elements, especially C, P, and S show a crossover from low to high FIP at ~10 eV in the SEPs but ~14 eV for the solar wind. Naively this seems to suggest cooler plasma from sunspots beneath active regions. More likely, if the ponderomotive force of Alfv\'en waves preferentially conveys low-FIP ions into the corona, the source plasma that eventually will be shock-accelerated as SEPs originates in magnetic structures where Alfv\'en waves resonate with the loop length on closed magnetic field lines. This concentrates FIP fractionation near the top of the chromosphere. Meanwhile, the source of the SSW may lie near the base of diverging open-field lines surrounding, but outside of, active regions, where such resonance does not exist, allowing fractionation throughout the chromosphere. We also find that energetic particles accelerated from the solar wind itself by shock waves at corotating interaction regions (CIRs), generally beyond 1 AU, confirm the FIP pattern of the solar wind.