Analytical models of coronal magnetic structures have been crucial for our understanding of MHD wave behaviour and in the development of the field of coronal seismology. In this talk, an analytical approach is used to derive the dispersion relation governing MHD waves in a 3D magnetic slab of homogeneous plasma enclosed on its two sides by non-magnetic, semi-infinite plasma of different densities and temperatures, thereby generalising the classic magnetic slab model, which is symmetric about the middle line of the slab.

The dispersion relation, unlike that governing the symmetric slab, cannot be factorised into sausage and kink eigenmodes. As the solar atmosphere is highly inhomogeneous, this has implications for traditional mode identification in a range of coronal structures. Varying the ratio of the external densities demonstrates mode convergence between sausage and kink modes in the wide slab limit, causing an unforeseen appearance of avoided crossings.

An analytical expression is derived which gives the ratio of the amplitudes of oscillation on each boundary of the slab as a function of the external density ratio and the parameters of the system. The results highlight the importance of studying MHD waves in non-homogeneous background atmospheres. The extension of this work to more complex systems (e.g. cylindrical loops) could have implications for coronal seismology and allow the further determination of difficult-to-measure parameters of magnetic structures.