title: Nonaxisymmetric anisotropy of solar wind turbulence.
abstract: A key prediction of turbulence theories is frame-invariance, and in magnetohydrodynamic (MHD) turbulence, axisymmetry of fluctuations with respect to the background magnetic field. Paradoxically the power in fluctuations in the turbulent solar wind are observed to be ordered with respect to the bulk macroscopic flow as well as the background magnetic field. Here, nonaxisymmetry across the inertial and dissipation ranges is quantified using in situ observations from Cluster. The observed inertial range nonaxisymmetry is reproduced by a "fly through" sampling of a direct numerical simulation of MHD turbulence. Furthermore, fly through sampling of a linear superposition of transverse waves with axisymmetric fluctuations generates the trend in nonaxisymmetry with power spectral exponent. The observed nonaxisymmetric anisotropy may thus simply arise as a sampling effect related to Taylor's hypothesis and is not related to the plasma dynamics itself.
authors.affiliation: Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, CV4 7AL, United Kingdom. a.j.turner@warwick.ac.uk
authors.forename: A J
authors.initials: AJ
authors.lastname: Turner
authors.forename: G
authors.initials: G
authors.lastname: Gogoberidze
authors.forename: S C
authors.initials: SC
authors.lastname: Chapman
authors.forename: B
authors.initials: B
authors.lastname: Hnat
authors.forename: W-C
authors.initials: WC
authors.lastname: Müller