Descripción: The evolution of the turbulent properties in the solar wind, during the travel of the parcels of fluid from the Sun to the outer heliosphere still has several unanswered questions. In this work, we will present results of an study on the dynamical evolution of turbulent magnetic fluctuations in the inner heliosphere. We focused on the anisotropy of the turbulence integral scale, measured parallel and perpendicular to the direction of the local mean magnetic field, and study its evolution according to the aging of the plasma parcels observed at different heliodistances. As diagnostic tool we employed single-spacecraft correlation functions computed with observations collected by Helios 1 & 2 probes over nearly one solar cycle. Our results are consistent with driving modes with wave-vectors parallel to the direction of the local mean magnetic field near the Sun, and a progressive spectral transfer of energy to modes with perpendicular wave-vectors. Advances made in this direction, as those presented here, will contribute to our understanding of the magnetohydrodynamical turbulence and Alfvénic-wave activity for this system, and will provide a quantitative input for models of charged solar and galactic energetic particles propagation and diffusion throughout the inner heliosphere. © 2012 International Astronomical Union.

Descripción: For over four decades, low frequency plasma and electromagnetic fluctuations have been observed in the solar wind (SW), making it the most completely studied case of magnetohydrodynamic turbulence in astrophysics, and the only one extensively and directly studied using in situ observations. Magnetohydrodynamic scale fluctuations in the SW are usually anisotropic with respect to the local mean magnetic field (B0). In this work, we present a study of turbulent properties in the inner heliosphere (solar wind between 0.3 and 1 AU) based on modeling in situ plasma and magnetic observations collected by Helios 1 and Helios 2 spacecraft throughout a solar minimum. We present preliminary results on the evolution of the spatial structure of the magnetic self-correlation function in the inner heliosphere. In particular we focus on the evolution of the integral length scale (λ) for magnetic fluctuations and on its anisotropy in the inertial range. As previously known from different studies, we confirm that near Earth λ ∥>λ⊥ (with λ∥ and λ⊥ representing the integral length in the parallel and perpendicular directions respect to B0, respectively). However, for lower distances to the Sun we found that λ∥<λ ⊥. Results presented here will help us to refine models used to describe the turbulence and waves activity in the inner heliosphere. © 2010 American Institute of Physics.