Chromospheric dynamics and turbulence regulate the solar FIP effect

TL;DR

This study combines hydrodynamic simulations with ponderomotive force calculations to explore how chromospheric turbulence and dynamics influence the solar FIP effect, revealing turbulence's role in suppressing element fractionation.

Contribution

It introduces a new open-source code, FIPpy, to model the impact of chromospheric dynamics on elemental fractionation, extending previous static models to dynamic conditions.

Findings

Ponderomotive force model remains valid under dynamic chromospheric conditions.

Turbulence suppresses element fractionation in the solar chromosphere.

Flares with increased turbulence can reduce FIP bias, affecting observed abundances.

Abstract

Elemental abundance variations in the solar corona, commonly characterised by First Ionisation Potential (FIP) bias, provide crucial diagnostics of chromospheric processes. The ponderomotive force model, which attributes fractionation to Alfv\'en wave propagation, has successfully reproduced observed abundance and fractionation patterns in various solar features. However, existing theoretical implementations rely on a static quiet Sun chromosphere, leaving the influence of chromospheric dynamics largely unexplored. We address this limitation by combining hydrodynamic simulations from HYDRAD with ponderomotive force calculations through FIPpy, a new open-source code. Comparing predictions between an initial VAL-C chromosphere and a heated chromosphere following impulsive nanoflare-like events, we show that the ponderomotive force model remains consistent under dynamic chromospheric conditions, while stronger changes in fractionation behaviour arise from variations in acoustic flux and turbulence. Most significantly, when acoustic wave flux drops below $\sim5\times10^6$ erg cm$^{-2}$ s$^{-1}$, mass-dependent thermal velocities dominate the fractionation process, producing counterintuitive patterns where Fe exceeds Ca in FIP bias, while high-FIP Ar shows fractionation. We demonstrate that any source of chromospheric turbulence will act to suppress fractionation. For flares, our results predict that the increased turbulence will suppress FIP bias, potentially explaining the observed abundance variations during flares. These findings suggest that coronal abundances and composition encode a sensitive balance between dominant mechanisms, determined by the ratio of ponderomotive acceleration to turbulent velocity.