Three-dimensional MHD wave propagation near a coronal null point: a new wave mode decomposition approach

TL;DR

This paper introduces a novel 3D MHD wave decomposition method that accurately identifies wave modes in the solar atmosphere, revealing how vortex-driven waves contribute to energy fluxes near coronal null points.

Contribution

The paper presents a new wave decomposition technique based on magnetic field-line geometry, improving wave mode identification in 3D MHD simulations and observations.

Findings

Vortex flows excite significant MHD waves in the solar corona.

Alfvén wave energy accumulates on the fan surface.

Fast wave energy concentrates near the null point.

Abstract

We present a new MHD wave decomposition method that overcomes the limitations of existing wave identification methods. Our method allows to investigate the energy fluxes in different MHD modes at different locations of the solar atmosphere as waves generated by vortex flows travel through the solar atmosphere and pass near the magnetic null. We simulate wave dynamics through a coronal null configuration and apply a rotational wave driver at our bottom photospheric boundary. To identify the wave energy fluxes associated with different MHD wave modes, we employ a wave-decomposition method that is able to uniquely distinguish different MHD modes. Our proposed method utilizes the geometry of an individual magnetic field-line in 3D space to separate out velocity perturbations associated with the three fundamental MHD waves. Our method for wave identification is consistent with previous flux-surface-based methods and gives expected results in terms of wave energy fluxes at various locations of the null configuration. We show that ubiquitous vortex flows excite MHD waves that contribute significantly to the Poynting flux in the solar corona. Alfv\'en wave energy flux accumulates on the fan surface and fast wave energy flux accumulates near the null point. There is a strong current density buildup at the spine and fan surface.The proposed method has advantages over previously utilized wave decomposition methods, since it may be employed in realistic simulations or magnetic extrapolations, as well as in real solar observations, whenever the 3D fieldline shape is known. The enhancement in energy flux associated with magneto-acoustic waves near nulls may have important implications in the formation of jets and impulsive plasma flows.