II. The effect of axisymmetric and spatially varying equilibria and flow on MHD wave modes: cylindrical geometry

Abstract

Magnetohydrodynamic (MHD) waves are routinely observed in the solar atmosphere. These waves are important in the context of solar physics as it is widely believed they can contribute to the energy budget of the solar atmosphere and are a prime candidate to contribute towards coronal heating. Realistic models of these waves are required representing observed configurations such that plasma properties can be determined more accurately which can not be measured directly. This work utilises a previously developed numerical technique to find permittable eigenvalues under different non-uniform equilibrium conditions in a Cartesian magnetic slab geometry. Here we investigate the properties of magnetoacoustic waves under non-uniform equilibria in a cylindrical geometry. Previously obtained analytical results are retrieved to emphasise the power and applicability of this numerical technique. Further case studies investigate the effect that a radially non-uniform plasma density and non-uniform plasma flow, modelled as a series of Gaussian profiles, has on the properties of different MHD waves. For all cases the dispersion diagrams are obtained and spatial eigenfunctions calculated which display the effects of the equilibrium inhomogeneity. It is shown that as the equilibrium non-uniformity is increased, the radial spatial eigenfunctions are affected and extra nodes introduced, similar to the previous investigation of a magnetic slab. Furthermore, azimuthal perturbations are increased with increasing inhomogeneity introducing vortical motions inside the waveguide. Finally, 2D and 3D representations of the velocity fields are shown which may be useful for observers for wave mode identification under realistic magnetic waveguides with ever increasing instrument resolution.

Modeling of Transverse Oscillations Driven by p-modes in Short Coronal Loops

“…In Figures 4(C) and (D), we plot two snapshots of the cross-section density profile (normalized) at the loop apex, with the horizontal velocity field overplotted. The distributions of the velocity vectors are consistent with the typical characteristics of the m = 1 kink mode, i.e., the "dipole-like" pattern (e.g., see Goossens et al 2014;Guo et al 2020;Skirvin et al 2022). Based on these results, we can conclude that there are dominant transverse kink oscillations excited in the loop.…”

Alfvénic Motions Arising from Asymmetric Acoustic Wave Drivers in Solar Magnetic Structures

“…During the time period corresponding to the first wave front from the driver, it is evident that the parallel vorticity is dominant over the perpendicular vorticity, which is the expected behavior of a transverse wave and may be related to resonant absorption of a standing kink mode (Goossens et al 2011). This is due to the coupling of transverse and azimuthal motions resulting in the amplitude of azimuthal motions increasing throughout the region of the non-uniform plasma (Skirvin et al 2022). However, at a later time, the values of perpendicular vorticity significantly exceed those of the parallel vorticity, hinting that the longitudinal waves dominate the dynamics of the system.…”

Small-scale solar jet formation and their associated waves and instabilities

“…The typical representation of a jet as a uniform magnetic cylinder with a background plasma flow is convenient in the analytic sense; however, in practice comes with many limitations. The lower solar atmosphere, which, as discussed, is replete with small-scale plasma jets, must be modelled with waveguides that have non-uniformity of plasma and background flow (Skirvin et al, 2021(Skirvin et al, , 2022 and a partially ionised plasma in which it is embedded. Furthermore, realistic jet models that vary with altitude/jet height are required as small-scale solar jets frequently propagate between regions of spatially varying plasma-β, which could dramatically affect the resulting wave modes and their properties.…”