Anysotropy evolution of solar wind magnetic and velocity fluctuations

M. E. RUIZ; DASSO, S.; W. H. MATTHAEUS; J.M. WEYGAND; E. MARSCH

El Leoncito, San Juan

Otro; 5º Escuela Internacional de Fisica Solar El Leoncito; 2011

The heliosphere is a natural wind tunnel to study several aspects of Magnetohydrodynamic (MHD) turbulence. In particular, the solar wind (SW) contains a very important level of fluctuations, which for large spatial scales can be studied in the framework of MHD turbulence. These MHD scale fluctuations are usually anisotropic, and frequently present different properties in regions of quasi-stationary SW with different bulk plasma parameters or in regions associated with the presence of transients (e.g., magnetic clouds). ‘In situ’ plasma and magnetic field properties are collected by spacecrafts in the SW and then observations are available to study SW-MHD fluctuations. It is known that spatial correlation functions of magnetic and velocity fluctuations, as well as anisotropies in the integral length scale, evolve in the inner heliosphere. In this work we present a study of the evolution of turbulence properties, analyzing the aging of plasma parcels observed at different heliodistances by the spacecrafts Helios 1-2. Our results are consistent with driving modes with wavevectors parallel to the direction of the local mean magnetic field near Sun, and a progressive spectral transfer of energy to modes with perpendicular wavevectors.