Enhanced phase mixing of Alfvén waves propagating in stratified and divergent coronal structures

Abstract

Corrected analytical solutions describing the enhanced phase mixing of Alfven waves propagating in divergent stratified coronal structures are presented. These show that the enhanced phase mixing mechanism can dissipate Alfven waves at heights less than half that is predicted by the previous analytical solutions. The enhanced phase mixing of 0.1 Hz harmonic Alfven waves propagating in strongly divergent, H_b=5 Mm, stratified coronal structures, H_rho=50 Mm, can fulfill 100% of an active region heating requirement, by generating viscous heating fluxes of F_H~2100 J /m^2 /s. The Alfven waves in this configuration are fully dissipated within 20 Mm, which is six times lower than would occur as a result of standard phase mixing in uniform magnetic fields. This results in the heating scale height, s_H, being lowered by a factor of six, to less than half of an active regions density scale height. Using the corrected analytical solutions it was found that, for a given wave frequency, the generation of a heating scale height of s_H<=50 Mm, by enhanced phase mixing in strongly divergent magnetic fields, requires a shear viscosity eight orders of magnitude lower, than required by standard phase mixing in uniform magnetic fields. It was also found that the enhanced phase mixing of observable, 0.01 rads /s Alfven waves, in strongly divergent magnetic fields, H_b=5 Mm, can generate heating scale heights within a density scale height, H_rho=50 Mm, using classical Braginskii viscosity. It is therefore not necessary to invoke anomalous viscosity in corona, if phase mixing takes place in strongly divergent magnetic fields. This study shows that the importance of enhanced phase mixing as a mechanism for dissipating Alfven waves in the solar corona (a stratified and divergent medium), has been seriously underestimated.

arXiv commentAccepted by A&A - 24th September 2007

References in corpus (6)

• Particle-In-Cell simulations of circularly polarised Alfvén wave phase mixing: a new mechanism for electron acceleration in collisionless plasmas
• A Three Dimensional Magnetohydrodynamic Pulse in a Transversely Inhomogeneous Medium
• A Strongly Nonlinear Alfvenic Pulse in a Transversely Inhomogeneous Medium
• Phase mixing of a three dimensional magnetohydrodynamic pulse
• A mechanism for parallel electric field generation in the MHD limit: possible implications for the coronal heating problem in the two stage mechanism
• A minimal model of parallel electric field generation in a transversely inhomogeneous plasma

Cited by in corpus (14)

• Energy transport and heating by torsional Alfvén waves propagating from the photosphere to the corona in the quiet Sun
• Phase Mixing of Nonlinear Visco-resistive Alfvén Waves
• The effect of twisted magnetic field on the resonant absorption of MHD waves in coronal loops
• Transition to turbulence in nonuniform coronal loops driven by torsional Alfven waves
• Enhanced Phase Mixing of Torsional Alfvén Waves in Stratified and Divergent Solar Coronal Structures, Paper II: Nonlinear Simulations
• Torsional Alfven waves in stratified and expanding magnetic flux tubes
• Transition to turbulence in nonuniform coronal loops driven by torsional Alfvén waves. II. Extended analysis and effect of magnetic twist
• Alfvén wave phase-mixing in flows: Why over-dense, solar coronal, open magnetic field structures are cool?
• 3D MHD simulation of linearly polarised Alfven wave dynamics in Arnold-Beltrami-Childress magnetic field
• Mixing of shear Alfven wave packets
• A potential magnetic field calculator for solar physics applications using staggered grids
• Phase mixing of standing Alfven waves with shear flows in solar spicules
• On the role of transition region on the Alfven wave phase mixing in solar spicules
• Enhanced Phase Mixing of Torsional Alfvén Waves in Stratified and Divergent Solar Coronal Structures, Paper I: Linear Solutions