Nonlinear Evolution of Short-wavelength Torsional Alfvén Waves

We analyze nonlinear evolution of torsional Alfvén waves in a straight magnetic flux tube filled in with a low-β plasma, and surrounded with a plasma of lower density. Such magnetic tubes model, in particular, a segment of a coronal loop or a polar plume. The wavelength is taken comparable to the tu...

Full description

Saved in:
Bibliographic Details
Published in:The Astrophysical journal 2017-05, Vol.840 (2), p.64
Main Authors: Shestov, S. V., Nakariakov, V. M., Ulyanov, A. S., Reva, A. A., Kuzin, S. V.
Format: Article
Language:English
Subjects:
ALFVEN WAVES
Amplitudes
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
COHERENT TUBE MODEL
Computational fluid dynamics
Computer simulation
COMPUTERIZED SIMULATION
Coronal loops
DENSITY
Evolution
Flow-density-speed relationships
LOW-BETA PLASMA
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETOACOUSTICS
MAGNETOHYDRODYNAMICS
magnetohydrodynamics (MHD)
Mathematical models
Nonlinear analysis
NONLINEAR PROBLEMS
Nonuniformity
Numerical simulations
Parallel flow
STAR EVOLUTION
STELLAR CORONAE
Stellar evolution
SUN
Sun: corona
Sun: oscillations
TUBES
Wave energy
Wave fronts
Wave power
WAVE PROPAGATION
WAVELENGTHS
waves
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:We analyze nonlinear evolution of torsional Alfvén waves in a straight magnetic flux tube filled in with a low-β plasma, and surrounded with a plasma of lower density. Such magnetic tubes model, in particular, a segment of a coronal loop or a polar plume. The wavelength is taken comparable to the tube radius. We perform a numerical simulation of the wave propagation using ideal magnetohydrodynamics. We find that a torsional wave nonlinearly induces three kinds of compressive flows: the parallel flow at the Alfvén speed, which constitutes a bulk plasma motion along the magnetic field, the tube wave, and also transverse flows in the radial direction, associated with sausage fast magnetoacoustic modes. In addition, the nonlinear torsional wave steepens and its propagation speed increases. The latter effect leads to the progressive distortion of the torsional wave front, i.e., nonlinear phase mixing. Because of the intrinsic non-uniformity of the torsional wave amplitude across the tube radius, the nonlinear effects are more pronounced in regions with higher wave amplitudes. They are always absent at the axes of the flux tube. In the case of a linear radial profile of the wave amplitude, the nonlinear effects are localized in an annulus region near the tube boundary. Thus, the parallel compressive flows driven by torsional Alfvén waves in the solar and stellar coronae, are essentially non-uniform in the perpendicular direction. The presence of additional sinks for the wave energy reduces the efficiency of the nonlinear parallel cascade in torsional Alfvén waves.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aa6c65