Numerical simulations of conversion to Alfven waves in solar active regions

TL;DR

This study uses 2.5D numerical simulations to investigate how magneto-acoustic waves convert into Alfvén waves in solar active regions, revealing the dependence on magnetic field inclination and the efficiency of energy transfer.

Contribution

It demonstrates the conditions under which magneto-acoustic waves convert into Alfvén waves, highlighting the role of magnetic field inclination and phase relations in this process.

Findings

Conversion efficiency peaks at 55-65 degrees inclination.

Maximum Alfvén flux is 2-3 times lower than acoustic flux.

Conversion is more effective at lower frequencies.

Abstract

We study the coupling of magneto-acoustic waves to Alven waves using 2.5D numerical simulations. In our experiment, a fast magnetoacoustic wave of a given frequency and wavenumber is generated below the surface. The magnetic field in the domain is assumed homogeneous and inclined. The efficiency of the conversion to Alfven waves near the layer of equal acoustic and Alfven speeds is measured calculating their energy flux. The particular amplitude and phase relations between the oscillations of magnetic field and velocity help us to demonstrate that the waves produced after the transformation and reaching upper atmosphere are indeed Alfven waves. We find that the conversion from fast magneto-acoustic waves to Alfven waves is particularly important for the inclination and azimuth angles of the magnetic field between 55 and 65 degrees, with the maximum shifted to larger inclinations for lower frequency waves. The maximum Alfven flux transmitted to the upper atmosphere is about 2-3 times lower than the corresponding acoustic flux.