Shestov, Sergei ; Voitenko, Yuri ; Zhukov, Andrei

Talk presented at Solar Wind XV on 2018-06-21

Abstract: Recent studies have revealed that the turbulence in magnetized plasmas is greatly affected by the Alfvén effect. The well-documented example is the solar-wind turbulence whose nature is essentially Alfvénic and turbulent fluctuations can be approximately described as Alfvén waves (AWs). We study using numerical MHD approach the commonly accepted presumption that the AW turbulence is generated by the collisions between counter-propagating AWs in the conditions typical for the solar wind. To this end, we launch in the simulation box two counterpropagating AWs and follow their evolution observing how the wave profiles are distorted during their collision. The initial waves are linearly polarized in two orthogonal planes, their cross-field amplitude profiles vary normally to their polarization planes, and their magnetic amplitudes are about 0.1 of the mean magnetic field. Polarization and spectral properties of the perturbations generated after a single collision between such AWs were analyzed in detail. We found that the perturbations had smaller-scale across the mean magnetic field compared to the original waves, and the perturbations had different polarizations. The obtained results confirm theoretical predictions that progressively larger cross-field wavenumbers are generated by the AW collisions. However, the observed amplitudes of the perturbations (1-2% of the original AW amplitudes) are not sufficient to generate the spectral transport typical for the strong turbulence proposed by Goldreich & Sridhar (1995). Instead, the obtained spectral transport implies conditions typical for the weak turbulence where many collisions are needed to generate a single cascade step. Further simulations are underway in an attempt to figure out if a single-step cascade can be generated by two counter-propagating AWs.

Keyword(s): turbulence, MHD, numerical simulations
Links: link
Funding: 3PRODPROBA3/3PRODPROBA3/3PRODPROBA3