Scaling Properties Of Small-Scale Anisotropy In The Solar Wind Turbulence By Multipoint Measurements

The scaling properties of magnetic field turbulence observed by Cluster in the solar wind are investigated. Using pairs of spacecraft the second order structure function tensor from high-resolution magnetic field measurements has been calculated as a function of spacecraft separation distance and the angle between the separation vector and the solar wind bulk flow direction. Recently there has been persistent experimental evidence that the return to isotropy at small scales invoked in the classical fluid turbulence does not hold in MHD turbulence. In this work, a method based on SO(3) decomposition is applied in order to separate the isotropic and anisotropic contributions to the magnetic field structure function tensor. The results from the analysis reveal that the anisotropy is present at small scales. A quantitative estimation of the degree of anisotropy and the scaling properties of the structure function tensor in different spatial directions are also obtained.