Solar Magneto-seismology of a Magnetic Slab in an Asymmetric Magnetic Environment

Abstract

Diagnosing the solar atmospheric plasma remains one of the major challenges in solar physics. In recent years, new methods have been developed to apply the powerful concept of solar magneto-seismology (SMS) to obtain information about plasma parameters in solar structures guiding magnetohydrodynamic (MHD) waves that would otherwise be difficult to measure. This paper uses the Cartesian model of a magnetic slab placed in an asymmetric magnetic environment to generalize recently discovered SMS techniques. Utilizing the fact that the asymmetric environment changes the character of the classical kink and sausage eigenmodes, we describe two spatial seismology methods built upon this mixed character of quasi-sausage and quasi-kink modes. First, we present the amplitude ratio technique, which compares the oscillation amplitudes measured at the two boundaries of the slab, and we provide expressions to estimate the internal Alfvén speed in the thin slab and in the incompressible plasma approximations. The second main technique relies on the changed distribution of wave power throughout the slab under the effect of waveguide asymmetry. This minimum perturbation shift technique is then also utilized to provide Alfvén speed estimates that depend on the plasma and magnetic parameters of the environment, as well as the measured slab width and oscillation frequency. Finally, we perform a brief investigation of how the amplitude ratio and the minimum perturbation shift depend on the different sources of waveguide asymmetry, and illustrate our findings with numerical results.