Nonlinear reflection process of linearly-polarized, broadband Alfvén waves in the fast solar wind

Abstract

Using one-dimensional numerical simulations, we study the elementary process of Alfvén wave reflection in a uniform medium, including nonlinear effects. In the linear regime, Alfvén wave reflection is triggered only by the inhomogeneity of the medium, whereas in the nonlinear regime, it can occur via nonlinear wave-wave interactions. Such nonlinear reflection (backscattering) is typified by decay instability. In most studies of decay instabilities, the initial condition has been a circularly polarized Alfvén wave. In this study we consider a linearly polarized Alfvén wave, which drives density fluctuations by its magnetic pressure force. For generality, we also assume a broadband wave with a red-noise spectrum. In the data analysis, we decompose the fluctuations into characteristic variables using local eigenvectors, thus revealing the behaviors of the individual modes. Different from circular-polarization case, we find that the wave steepening produces a new energy channel from the parent Alfvén wave to the backscattered one. Such nonlinear reflection explains the observed increasing energy ratio of the sunward to the anti-sunward Alfvénic fluctuations in the solar wind with distance against the dynamical alignment effect.

31 pages, 12 figures, accepted by The Astrophysical Journal

References in corpus (4)

• Athena: A New Code for Astrophysical MHD
• Self-consistent Coronal Heating and Solar Wind Acceleration from Anisotropic Magnetohydrodynamic Turbulence
• The Turbulent Heating Rate in Strong MHD Turbulence with Nonzero Cross Helicity
• Time-Dependent Turbulent Heating of Open Flux Tubes in the Chromosphere, Corona, and Solar Wind

Cited by in corpus (8)

• MHD Waves in open coronal structures
• A self-consistent model of the coronal heating and solar wind acceleration including compressible and incompressible heating processes
• Frequency-dependent Alfvén-wave propagation in the solar wind: Onset and suppression of parametric decay instability
• Stellar Winds and Coronae of Low-mass Pop. II/III Stars
• Anisotropic magnetohydrodynamic turbulence driven by parametric decay instability: the onset of phase mixing and Alfvén wave turbulence
• Evidence for Parameteric Decay Instability in the Lower Solar Atmosphere
• Flux-tube-dependent propagation of Alfvén waves in the solar corona
• Exploring Complexity Measures for Analysis of Solar Wind Structures and Streams