The FIP and Inverse FIP Effects in Solar Flares

TL;DR

This paper explores the mechanisms behind the FIP and Inverse FIP effects in solar flares, focusing on wave refraction and magnetohydrodynamic processes to explain observed elemental abundance variations.

Contribution

It provides a detailed physical model of FIP and Inverse FIP fractionation based on wave refraction and magnetohydrodynamics, aligning well with recent observations.

Findings

Model explains FIP and Inverse FIP effects through wave refraction.

Good agreement with observational data from recent studies.

Highlights the role of wave origin and propagation in elemental fractionation.

Abstract

The Inverse First Ionization Potential (FIP) Effect, the depletion in coronal abundance of elements like Fe, Mg, and Si that are ionized in the solar chromosphere relative to those that are neutral, has been identified in several solar flares. We give a more detailed discussion of the mechanism of fractionation by the ponderomotive force associated with magnetohydrodynamic waves, paying special attention to the conditions in which Inverse FIP fractionation arises in order to better understand its relation to the usual FIP Effect, i.e. the enhancement of coronal abundance of Fe, Mg, Si, etc. The FIP Effect is generated by parallel propagating Alfv\'en waves, with either photospheric, or more likely coronal, origins. The Inverse FIP Effect arises as upward propagating fast mode waves with an origin in the photosphere or below, refract back downwards in the chromosphere where the Alfv\'en speed is increasing with altitude. We give a more physically motivated picture of the FIP fractionation, based on the wave refraction around inhomogeneities in the solar atmosphere, and inspired by previous discussions of analogous phenomena in the optical trapping of particles by laser beams. We apply these insights to modeling the fractionation and find good agreement with the observations of Katsuda et al. (2020; arXiv:2001.10643) and Dennis et al. (2015; arXiv:1503.01602).