Nonlinear Interactions in Spherically Polarized Alfv\'{e}nic Turbulence
Abstract
Turbulent magnetic field fluctuations observed in the solar wind often maintain a constant magnitude condition accompanied by spherically polarized velocity fluctuations; these signatures are characteristic of large-amplitude Alfv\'{e}n waves. Nonlinear energy transfer in Alfv\'{e}nic turbulence is typically considered in the small-amplitude limit where the constant magnitude condition may be neglected; in contrast, nonlinear energy transfer in the large-amplitude limit remains relatively unstudied. We develop a method to analyze finite-amplitude turbulence through studying fluctuations as constant magnitude rotations in the stationary wave (de Hoffmann-Teller) frame, which reveals that signatures of finite-amplitude effects exist deep into the MHD range. While the dominant fluctuations are consistent with spherically-polarized large-amplitude Alfv\'{e}n waves, the subdominant mode is relatively compressible. Signatures of nonlinear interaction between the finite-amplitude spherically polarized mode with the subdominant population reveal highly aligned transverse components. In theoretical models of Alfv\'{e}nic turbulence, alignment is thought to reduce nonlinearity; our observations require that alignment is sufficient to either reduce shear nonlinearity such that non-Alfv\'{e}nic interactions may be responsible for energy transfer in spherically polarized states, or that counter-propagating fluctuations maintain anomalous coherence, which is a predicted signature of reflection-driven turbulence.
Cite
@article{arxiv.2110.11454,
title = {Nonlinear Interactions in Spherically Polarized Alfv\'{e}nic Turbulence},
author = {Trevor A. Bowen and Samuel T. Badman and Stuart D. Bale and Thierry Dudok de Wit and Timothy S. Horbury and Kristopher G. Klein and Davin Larson and Alfred Mallet and Lorenzo Matteini and Michael D. McManus and Jonathan Squire},
journal= {arXiv preprint arXiv:2110.11454},
year = {2021}
}