Vector Alignment and Dimensionality in Turbulence
Alignement de vecteurs et dimensionnalité en turbulence
Résumé
Rapid local directional alignment of different vector quantities has been observed in incompressible turbulence, either in MHD or in fluid turbulence, in both direct numerical simulations or in Solar wind data, and these alignments weaken the nonlinear terms with respect to those expected for Gaussian random fields. Evidence are based on the comparison of the probability distributions of the angle between vectors to those for independent isotropic three-dimensional vectors. We show that this apparent alignment can also be attributed to a local reduction of the dimensionality of the structures towards bidimensionality, leading to an increased probability of finding vectors close to alignment, compared to the spatial three-dimensional case. This interpretation is checked in Helios-2 Fast and Slow Solar wind data.
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