Characterization of the turbulent magnetic integral length in the solar wind: from 0.3 to 5 astronomical units

Abstract

The solar wind is a structured and complex system, in which the fields vary strongly over a wide range of spatial and temporal scales. As an example, the turbulent activity in the wind affects the evolution in the heliosphere of the integral turbulent scale or correlation length [λ], usually associated with the breakpoint in the turbulent-energy spectrum that separates the inertial range from the injection range. This large variability of the fields demands a statistical description of the solar wind. We study the probability distribution function (PDF) of the magnetic-autocorrelation lengths observed in the solar wind at different distances from the Sun. We used observations from the Helios, ACE, and Ulysses spacecraft. We distinguished between the usual solar wind and one of its transient components (interplanetary coronal mass ejections, ICMEs), and also studied solar-wind samples with low and high proton beta [βp]. We find that in the last three regimes the PDF of λ is a log-normal function, consistent with the multiplicative and nonlinear processes that take place in the solar wind, the initial λ (before the Alfvénic point) being larger in ICMEs.