A probabilistic approach to heterogeneity in space plasmas: the case of magnetic field intensity in solar wind

G Consolini,P De Michelis,B Bavassano

doi:10.5194/npg-16-265-2009

Abstract

Abstract. Since the early 90s it was shown that Probability Distribution Functions (PDFs) of small scale differences (fluctuations) of several quantities in space plasmas display significant departures from Gaussianity. The non-Gaussian shape of PDFs was ascribed to intermittency and discussed in the framework of intermittent MHD turbulence. Here, we put the attention to the PDF of magnetic field intensity instead of its differences showing how the PDF of such quantity in a quiet solar wind can be related with the occurrence of heterogeneity. In detail, we derive the shape of the PDFs by simple statistical considerations based on the concept of subordination in probability theory. An interpretation and a discussion in terms of existing coherent magnetic structures in a mechanical near-equilibrium state are also presented.

Highlights

In the last 20 years we experienced changes in the approach to the study of solar-system space plasmas
To test functional expressions derived in the previous Section, we investigate the Probability Distribution Functions (PDFs) of the fluctuations of the magnetic field intensity at short time scale in the solar wind ψ(δx)
– the observed PDF of the magnetic field intensity is in agreement with the proposed randomized Weibull;

Summary

Introduction

In the last 20 years we experienced changes in the approach to the study of solar-system space plasmas. Due to the ubiquitousness of non-Gaussian distributions in many physical scenarios several models have been proposed This is true in the framework of hydrodynamic and magnetohydrodynamic turbulence, where different approaches have been proposed to understand the leptokurtic nature of small-scale PDFs (Castaing et al, 1990; Frisch and Sornette, 1997; Beck and Cohen, 2003; Leubner and Voros, 2005a, b). The departure from Gaussian distributions in space plasmas is generally interpreted as the signature of intermittent MHD turbulence, since the mid-90s it was proposed that the existence of coherent magnetic and/or plasma structures might play a relevant role. The paper is organized as follows: Sect. 2 introduces a probabilistic model for heterogeneous systems and some basic concepts dealing with statistical subordination; Sect. 3 shows a comparison between the proposed model and observations of interplanetary magnetic field intensity in a longstanding slow solar-wind period; in Sect. 4 we trace out our conclusions

Heterogeneity and rare event statistics

Data description

Results

Conclusions