Evidences for extended self-similarity in hydromagnetic turbulence

We investigate the occurrence of Extended Self-Similarity in the Solar Wind Magnetohydrodynamic (MHD) turbulence by using Hellos 2 bulk velocity data recorded in the inner heliosphere at five different heliocentric distances. For each analysed time interval, we compute the sets of scaling exponents for the q-th order velocity structure functions and we show that these sets turn out to be to a good approximation the same whatever the different heliocentric distances. This result shows that a universal non gaussian probability distribution function, which depends on a unique parameter, describes the velocity differences in a MHD turbulent flow also outside the inertial range and in presence of intermittency. Moreover comparing the values of the obtained scaling exponents with those derived from the existing theoretical models of intermittency, we can infer that the most intermittent MHD structures should be two-dimensional current sheets.