MHD Wave Propagation in the Neighbourhood of Two Null Points

TL;DR

This study investigates how fast magnetoacoustic and Alfvén waves behave near two null points in a low-beta plasma, revealing wave attraction, accumulation, and potential heating sites in the solar corona.

Contribution

It provides new insights into wave behavior around multiple null points in a more complex magnetic configuration than previously studied.

Findings

Fast waves are attracted to null points and split, accumulating energy at each null.

Alfvén waves accumulate along separatrices, indicating specific heating regions.

Wave accumulation occurs at specific topological features, affecting coronal heating understanding.

Abstract

The nature of fast magnetoacoustic and Alfv\'en waves is investigated in a zero $\beta$ plasma in the neighbourhood of a pair of two-dimensional null points. This gives an indication of wave propagation in the low $\beta$ solar corona, for a more complicated magnetic configuration than that looked at by McLaughlin & Hood (2004). It is found that the fast wave is attracted to the null points and that the front of the wave slows down as it approaches the null point pair, with the wave splitting and part of the wave accumulating at one null and the rest at the other. Current density will then accumulate at these points and ohmic dissipation will then extract the energy in the wave at these points. This suggests locations where wave heating will occur in the corona. The Alfv\'en wave behaves in a different manner in that the wave accumulates along the separatrices. Hence, the current density will accumulate at this part of the topology and this is where wave heating will occur. However, the phenomenon of wave accumulation at a specific place is a feature of both wave types, and illustrates the importance of studying the topology of the corona when considering MHD wave propagation.