Multi-scale Structural Analysis of Magnetosheath Turbulence with Rank Ordered Fractals

English Abstract:

In-situ measurements of magnetic field fluctuations in the terrestrial magnetosheath revealed fundamental differences between the quasi-perpendicular and quasi-parallel geometries. In the quasi-parallel case the fluctuations are strongly intermittent as suggested by the scale dependent non-Gaussian wings of the probability distribution functions (PDFs) and the scale dependent behaviour of their fourth order moment. A previous study of the intermittent magnetosheath turbulence for a quasi-parallel geometry (Sundkvist et al., PRL, 2007) discussed the energy dissipation in terms of reconnecting thin current sheets scaling with the local Larmor radius. The Rank Ordered Multifractal Analysis (ROMA) is a data analysis method constructed with the aim of identifying the various individual fractal behaviour of multifractal fluctuations (Wu and Chang, Phys Rev E, 2008). ROMA is capable of disentangling the ranges of fluctuations that exhibit the same fractal (self-similar) dimension in terms of the local invariant property based on the scaled amplitude of fluctuations and thereby identifying the different regimes of fluctuations (e.g., persistency ) and physical processes (e.g., kinetic/MHD). A ROMA analysis of the intermittent turbulence in the magnetosheath describing the multiscale and dissipation behaviour over ranges of scales, in the coarse-grained sense, will be presented. We will also discuss the relevance of the analysis for general studies of turbulence in solar system plasmas.

Research supported by the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no 313038/STORM, and a national grant CNCS–UEFISCDI, project number PN-II-ID-PCE-2012-4-0418.