On the Variation of Intermittency of Fast and Slow Solar Wind With Radial Distance, Heliospheric Latitude, and Solar Cycle

Anna Wawrzaszek,Marius Echim

doi:10.3389/fspas.2020.617113

Abstract

Intermittency, an important property of astrophysical plasma turbulence, is studied extensively during last decades from in-situ measurements of the solar wind plasma and magnetic field in the ecliptic plane and at higher latitudes, and heliocentric distances between 0.3 and 5 Astronomical Units. In this paper, we review the main findings on intermittency derived from investigation of solar wind turbulence for the inertial range of scales. It turns out that our current knowledge on the evolution of intermittency in the heliosphere is based on two missions, Helios two and Ulysses. We discuss the importance of data selection methodologies and applications for heliospheric spacecraft, the different data analysis techniques (the anomalous scaling of the structure function, the non-Gaussianity of the probability distribution functions, the local intermittency measure estimated from a wavelet representation and the multifractal spectrum). Studies show that Alvénic solar wind is less intermittent but reveals increase with the radial distance. Moreover, intermittency is stronger for the magnetic than for velocity fluctuations and is considered to be responsible for the increase with the radial distance of the anisotropy of magnetic fluctuations. The intermittency of fast solar wind at solar minimum decreases with latitude. Finally, the level of intermittency in the solar wind depends on solar cycle phase, reflecting the changes of the state of solar wind and suggesting that the deeper study of origin of fast and slow wind can further improve our understanding of the intermittency.

Highlights

The solar wind is considered as natural laboratory to study turbulence of astrophysical plasmas (Bruno and Carbone, 2013, and references therein)
We summarize the observations of MHD intermittency in the solar wind, and discuss how intermittency changes with the type of solar wind, the radial distance, the heliolatitude, and solar cycle
In this review we discuss recent findings on solar wind inertial range intermittency observed over a large range of heliocentric distances and latitudes, for different levels of solar activity

Summary

INTRODUCTION

The solar wind is considered as natural laboratory to study turbulence of astrophysical plasmas (Bruno and Carbone, 2013, and references therein). The irregularity of the energy transfer rate (see, e.g., Marsch et al, 1996; Horbury et al, 1997) leads to the phenomenon of intermittency (from Latin intermitere, to interrupt) This type of irregularity represents a violation of the fundamental hypothesis adopted to derive the classical model of Kolmogorov turbulence and is generally described as a deviation from the perfect selfsimilarity Due to the relatively reduced time resolution of most of solar wind data, the methods mentioned above were applied to study intermittency of the inertial range turbulence (e.g., Burlaga, 1991; Marsch and Liu, 1993; Tu et al, 1996; Sorriso-Valvo et al, 1999; Bruno et al, 2003; Wawrzaszek et al, 2015; Wawrzaszek et al, 2019). The study of intermittency in the MHD range of scales is crucial and complementary to investigation of kinetic scales reported recently by (e.g., Perri et al, 2012; Wan et al, 2012; Sorriso-Valvo et al, 2017)

Radial Evolution of Intermittency in the Ecliptic

Radial Dependence of Intermittency Outside the Ecliptic

Latitudinal Dependence and Solar Cycle Effect

Method

SUMMARY AND PERSPECTIVE