Ponderomotive Acceleration in Coronal Loops

TL;DR

This paper demonstrates through numerical simulations that ponderomotive acceleration naturally occurs in solar coronal loops as a byproduct of coronal heating, potentially explaining the FIP effect observed in the solar corona.

Contribution

It provides the first detailed numerical evidence that ponderomotive acceleration occurs in coronal loops due to magnetic reconnection and coronal heating processes.

Findings

Ponderomotive acceleration occurs in coronal loops with realistic magnetic field strengths.

The acceleration is intermittent and linked to magnetic reconnection events.

Simulations show the acceleration's magnitude and direction consistent with FIP effect requirements.

Abstract

Ponderomotive acceleration has been asserted to be a cause of the First Ionization Potential (FIP) effect, the by now well known enhancement in abundance by a factor of 3-4 over photospheric values of elements in the solar corona with FIP less than about 10 eV. It is shown here by means of numerical simulations that ponderomotive acceleration occurs in solar coronal loops, with the appropriate magnitude and direction, as a "byproduct" of coronal heating. The numerical simulations are performed with the HYPERION code, which solves the fully compressible three-dimensional magnetohydrodynamic equations including nonlinear thermal conduction and optically thin radiation. Numerical simulations of a coronal loops with an axial magnetic field from 0.005 Teslas to 0.02 Teslas and lengths from 25000 km to 75000 km are presented. In the simulations the footpoints of the axial loop magnetic field are convected by random, large-scale motions. There is a continuous formation and dissipation of field-aligned current sheets which act to heat the loop. As a consequence of coronal magnetic reconnection, small scale, high speed jets form. The familiar vortex quadrupoles form at reconnection sites. Between the magnetic footpoints and the corona the reconnection flow merges with the boundary flow. It is in this region that the ponderomotive acceleration occurs. Mirroring the character of the coronal reconnection, the ponderomotive acceleration is also found to be intermittent.