Resonant Absorption of Axisymmetric Modes in Twisted Magnetic Flux Tubes

Abstract

It has been shown recently that magnetic twist and axisymmetric MHD modes are ubiquitous in the solar atmosphere and therefore, the study of resonant absorption for these modes have become a pressing issue as it can have important consequences for heating magnetic flux tubes in the solar atmosphere and the observed damping. In this investigation, for the first time, we calculate the damping rate for axisymmetric MHD waves in weakly twisted magnetic flux tubes. Our aim is to investigate the impact of resonant damping of these modes for solar atmospheric conditions. This analytical study is based on an idealized configuration of a straight magnetic flux tube with a weak magnetic twist inside as well as outside the tube. By implementing the conservation laws derived by \cite{Sakurai:1991aa} and the analytic solutions for weakly twisted flux tubes obtained recently by \cite{Giagkiozis:2015apj}, we derive a dispersion relation for resonantly damped axisymmetric modes in the spectrum of the Alfvén continuum. We also obtain an insightful analytical expression for the damping rate in the long wavelength limit. Furthermore, it shown that both the longitudinal magnetic field and the density, which are allowed to vary continuously in the inhomogeneous layer, have a significant impact on the damping time. Given the conditions in the solar atmosphere, resonantly damped axisymmetric modes are highly likely to be ubiquitous and play an important role in energy dissipation. We also suggest that given the character of these waves, it is likely that they have already been observed in the guise of Alfvén waves.

References in corpus (3)

• Alfven Waves in the Lower Solar Atmosphere
• Transverse oscillations of flowing prominence threads observed with Hinode
• Axisymmetric Modes in Magnetic Flux Tubes with Internal and External Magnetic Twist

Cited by in corpus (9)

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• Resonant absorption in expanding coronal magnetic flux tubes with uniform density
• Resonant absorption of surface sausage and surface kink modes under photospheric conditions
• Small-scale solar jet formation and their associated waves and instabilities
• The effect of a twisted magnetic field on the phase mixing of the kink magnetohydrodynamic waves in coronal loops
• Resonant absorption of kink oscillations in coronal flux tubes with continuous magnetic twist
• The Effect of Flow and Magnetic Twist on Resonant Absorption of Slow MHD Waves in Magnetic Flux Tubes
• Oblique Quasi-Kink Modes in Solar Coronal Slabs Embedded in an Asymmetric Magnetic Environment: Resonant Damping, Phase and Group Diagrams