Generation of Alfven Waves by Magnetic Reconnection

TL;DR

This study uses 2.5D MHD simulations to analyze how magnetic reconnection generates Alfven and magneto-acoustic waves, quantifying their energy contributions and implications for solar phenomena.

Contribution

It provides the first detailed quantification of energy partitioning between Alfven and magneto-acoustic waves during magnetic reconnection with a guide field.

Findings

Alfven waves carry up to 38.9% of released magnetic energy.

Magneto-acoustic waves can carry up to 75% of the energy depending on the angle.

Energy fluxes of waves show similar time evolution regardless of the guide field angle.

Abstract

In this paper, results of 2.5-dimensional magnetohydrodynamical simulations are reported for the magnetic reconnection of non-perfectly antiparallel magnetic fields. The magnetic field has a component perpendicular to the computational plane, that is, guide field. The angle theta between magnetic field lines in two half regions is a key parameter in our simulations whereas the initial distribution of the plasma is assumed to be simple; density and pressure are uniform except for the current sheet region. Alfven waves are generated at the reconnection point and propagate along the reconnected field line. The energy fluxes of the Alfven waves and magneto-acoustic waves (slow mode and fast mode) generated by the magnetic reconnection are measured. Each flux shows the similar time evolution independent of theta. The percentage of the energies (time integral of energy fluxes) carried by the Alfven waves and magneto-acoustic waves to the released magnetic energy are calculated. The Alfven waves carry 38.9%, 36.0%, and 29.5% of the released magnetic energy at the maximum (theta=80^\circ) in the case of beta=0.1, 1, and 20 respectively, where beta is the plasma beta (the ratio of gas pressure to magnetic pressure). The magneto-acoustic waves carry 16.2% (theta=70^\circ), 25.9% (theta=60^\circ), and 75.0% (theta=180^\circ) of the energy at the maximum. Implications of these results for solar coronal heating and acceleration of high-speed solar wind are discussed.