STATISTICAL ANALYSIS OF DISCONTINUITIES IN SOLAR WIND ACE DATA AND COMPARISON WITH INTERMITTENT MHD TURBULENCE

A Greco,P Dmitruk,S Servidio,W H Matthaeus,P Chuychai

doi:10.1088/0004-637x/691/2/l111

Abstract

The comparison between Advanced Composition Explorer (ACE) solar wind data and simulations of magnetohydrodynamic (MHD) turbulence shows a good agreement in the waiting-time analysis of magnetic field increments. Similarity between classical discontinuity identification and intermittency analysis suggests a dynamical connection between solar wind discontinuities and intermittent MHD turbulence. Probability distribution functions of increments in ACE data and in simulations reveal a robust structure consisting of small random currents, current cores, and intermittent current sheets. This adds to evidence that solar wind magnetic structures may emerge fast and locally from MHD turbulence.

Highlights

Simulations of magnetohydrodynamic (MHD) turbulence (Politano et al 1998; Biskamp & Muller 2000) and solar wind observations (Burlaga 1991; Marsch & Tu 1994; Horbury et al 1997; Sorriso-Valvo et al 1999; Burlaga et al 2006) each show evidence for intermittency in the form of characteristic small-scale structures
In this Letter, we further examine the link between intermittent turbulence and MHD discontinuities, directly comparing statistical analysis from solar wind data and simulations of MHD turbulence
We show that the probability density functions of waiting times (WTs) between classical discontinuities identified in the solar wind and in the MHD simulations are essentially the same on inertial scales

Summary

INTRODUCTION

Simulations of magnetohydrodynamic (MHD) turbulence (Politano et al 1998; Biskamp & Muller 2000) and solar wind observations (Burlaga 1991; Marsch & Tu 1994; Horbury et al 1997; Sorriso-Valvo et al 1999; Burlaga et al 2006) each show evidence for intermittency in the form of characteristic small-scale structures. A possibly related phenomenon is the well-known frequent appearance of structures traditionally identified as magnetic discontinuities in the solar wind (Burlaga 1968; Tsurutani & Smith 1979) (TS); for a review see Ness & Burlaga (2001). It is possible that a substantial fraction of the observed discontinuities may be related to flux tube boundaries and intermittent structures that appear spontaneously in MHD turbulence (Matthaeus & Montgomery 1980; Matthaeus & Lamkin 1986; Carbone et al 1990; Veltri 1999; Vasquez et al 2007; Servidio et al 2008). Since we have shown in Greco et al (2008) that MHD turbulence produces intermittent current sheets in sufficient numbers to account for many of the jumps observed at small scales, here we cannot rule out that some of the discontinuities identified in the solar wind are produced by a turbulent MHD cascade

SIMULATIONS AND SOLAR WIND DATA

IDENTIFICATION OF EVENTS

ANALYSIS OF THE STRUCTURE OF THE PDFS

CONCLUSIONS