MHD Mode Conversion around a 2D Magnetic Null Point

TL;DR

This paper investigates the process of magnetohydrodynamic mode conversion near a 2D magnetic null point, combining numerical simulations and analytical methods to understand wave behavior in the solar corona.

Contribution

It provides a detailed analysis of wave mode conversion at a coronal null point using combined numerical and analytical approaches, advancing understanding of wave dynamics in solar physics.

Findings

Mode conversion occurs at the null point where sound and Alfvén speeds are equal.

Numerical simulations show the passage of slow waves and the generation of fast waves.

Analytical WKB analysis successfully tracks wave modes through the domain.

Abstract

Mode conversion occurs when a wave passes through a region where the sound and Alfven speeds are equal. At this point there is a resonance, which allows some of the incident wave to be converted into a different mode. We study this phenomenon in the vicinity of a two-dimensional, coronal null point. As a wave approaches the null it passes from low- to high-beta plasma, allowing conversion to take place. We simulate this numerically by sending in a slow magnetoacoustic wave from the upper boundary; as this passes through the conversion layer a fast wave can clearly be seen propagating ahead. Numerical simulations combined with an analytical WKB investigation allow us to determine and track both the incident and converted waves throughout the domain.