Abstract
Abstract. This paper demonstrates that intermittent magnetic field fluctuations in the plasma sheet exhibit transitory, localized, and multi-scale features. We propose a multifractal-based algorithm, which quantifies intermittence on the basis of the statistical distribution of the "strength of burstiness", estimated within a sliding window. Interesting multi-scale phenomena observed by the Cluster spacecraft include large-scale motion of the current sheet and bursty bulk flow associated turbulence, interpreted as a cross-scale coupling (CSC) process.Key words. Magnetospheric physics (magnetotail; plasma sheet) – Space plasma physics (turbulence)
Highlights
The study of turbulence in near-Earth cosmic plasma is important in many respects
We proposed a windowed multifractal method to quantify local intermittence of magnetic field fluctuations obtained by Cluster
We have shown as Cluster passes through different plasma regions, physical processes exhibit non-stationary intermittence properties on MHD and small, possibly kinetic scales
Summary
The study of turbulence in near-Earth cosmic plasma is important in many respects. Turbulence, being in its nature a multi-scale phenomenon, may influence the transfer processes of energy, mass and momentum on both MHD and kinetic scales. Intermittence refers to processes which display “sporadic activity” during only a small fraction of the considered time or space This is the case in non-homogeneous turbulence, where the distribution of energy dissipation regions is sporadic and probability distributions of measurable quantities are long-tailed with significant departures from Gaussianity. Angelopoulos et al (1999a) have proposed that BBF-generated intermittent turbulence can alter transport processes in the plasma sheet and may represent a way for cross-scale coupling (CSC) to take place. These facts call for a method which allows for analysis of both intermittence and multi-scale properties of fluctuations. Using both magnetic field and ion velocity data from Cluster, we will show that BBF-associated “magnetic turbulence” exhibits clear signatures of cross-scale energisation
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