The First Ionization Potential Effect from the Ponderomotive Force: On the Polarization and Coronal Origin of the Alfven Waves

TL;DR

This paper explores how the ponderomotive force from Alfven waves originating in the chromosphere and corona influences ion-neutral separation, explaining the First Ionization Potential Effect observed in the solar atmosphere.

Contribution

It models the dependence of FIP fractionation on Alfven wave types and origins, highlighting the significance of coronal-origin waves near resonance for matching observed abundances.

Findings

Shear Alfven waves better reproduce observed fractionations.

Coronal-origin Alfven waves near resonance match observed abundances.

Reflections of Alfven waves cause FIP fractionation via the ponderomotive force.

Abstract

We investigate in more detail the origin of chromospheric Alfven waves that give rise to the separation of ions and neutrals, the First Ionization Potential Effect (FIP), through the action of the ponderomotive force. In open field regions, we model the dependence of fractionation on the plasma upflow velocity through the chromosphere for both shear (or planar) and torsional Alfven waves of photospheric origin. These differ mainly through their parametric coupling to slow mode waves. Shear Alfven waves appear to reproduce observed fractionations for a wider range of model parameters, and present less of a "fine-tuning" problem than do torsional waves. In closed field regions, we study the fractionations produced by Alfven waves with photospheric and coronal origins. Waves with a coronal origin, at or close to resonance with the coronal loop, offer a significantly better match to observed abundances than do photospheric waves, with shear and torsional waves in such a case giving essentially indistinguishable fractionations. Such coronal waves are likely the result of a nanoflare coronal heating mechanism, that as well as heating coronal plasmas releases Alfven waves that can travel down to loop footpoints and cause FIP fractionation through the ponderomotive force as they reflect from the chromosphere back into the corona.