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Nonlinear damping of surface Alfvén waves and transition to (uni)turbulence: statistical analysis

Presentation #105.12 in the session Ambient Solar Atmosphere Posters.

Published onSep 18, 2023
Nonlinear damping of surface Alfvén waves and transition to (uni)turbulence: statistical analysis

This comprehensive investigation dives deep into the complex dynamics of magnetohydrodynamic (MHD) uniturbulence, focusing on the unidirectional propagation of surface Alfvén waves under a Cartesian equilibrium model with a constant magnetic field and piece-wise constant density. In this study, we examine uniturbulence’s intricacies using both analytical methods and 3D ideal MHD simulations, analyzing statistical relationships between length scales and the mechanisms for transferring turbulent energy. The discontinuous equilibrium density changes are the source of surface Alfvén waves, which, due to density variation across the magnetic field, generate uniturbulence. The damping of these surface Alfvén waves, determined through the Elsässer formulation, is intricately analyzed, providing expressions for the wave energy density, energy cascade, and damping time.

Applying state-of-the-art statistical methodologies, including power spectrum analysis, radially averaged Fourier transform, and kurtosis, we reveal the kinetic and magnetic energy spatiotemporal distributions in uniturbulent flows. Our findings show that the inertial range of the perpendicular kinetic energy and magnetic energy along the direction of wave propagation exhibit a progressive change in slope values, ultimately approaching the widely-recognized values of -5/3 and -3/2, respectively. This key insight underscores the complex interaction between MHD turbulence and the magnetic field as they propagate in the flow direction. Furthermore, we expose the critical role of density contrast and Yaglom’s law in energy transfer mechanisms. The non-Gaussian behavior of the flow field over time and different length scales offers a novel perspective on uniturbulence dynamics, highlighting the intricate interplay between varying scales.

Our study provides an enhanced understanding of uniturbulence, establishing a solid ground for future investigations. The analytical and simulation results demonstrate that the damping time is inversely proportional to the amplitude of surface Alfvén waves and the density contrast, providing valuable insights into the heating mechanisms of coronal plasma. These findings not only contribute to the understanding of uniturbulence in the context of surface Alfvén waves but also offer a springboard for exploring more complex wave systems such as kink waves in cylinders.

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