Description
We study the behaviour of the fast magnetoacoustic wave in a magnetic topology containing an X-type null point and focus on the propagation of these waves in close proximity to the null point. We use the Lare2D numerical code to drive a linear fast magnetoacoustic wave into the topology, and investigate the behaviour, finding that the Alfvén speed profile plays a critical role. We also solve the MHD equations analytically, using the WKB approximation and Charpit’s method, and find strong agreement between the analytical WKB and the numerical simulations.
In this work, we consider the effects of gravitational stratification and find that introducing a stratified density profile shatters the symmetry of the system, altering the Alfvén speed profile, and as such, altering the behaviour of the wave. We investigate a variety of levels of stratification, as well as exploring the new lack of symmetry, and we continue to use the WKB to provide analytical insight. Whilst we continue to see excellent agreement between the analytical WKB and the numerical simulations, we also find and examine behaviours that are not present in the non-stratified case, including some significant unexpected behaviour.
