STORM - Solar system plasma Turbulence:  Observations, inteRmittency and Multifractals

Turbulence, Intermittency and Multifractals in the solar wind, at solar maximum and solar minimum

This work package is devoted to the analysis of solar wind intermittent turbulence in the solar wind and will provide on the one hand a quantitative description of the turbulence, of its inertial range and the properties of energy transfer and on the other hand will provide an estimation of the turbulence upstream the outer layers of the planetary plasma environment – an input for space weather events in case of the Earth.

The data bases to be used are provided by the core mission, Ulysses, Cluster and Venus Express, and also by Giotto (at earlier dates), Rosetta, Cassini. The Power Spectral Densities will be systematically computed for the selected data sets and the spectral index will be evaluated and catalogued. Then the Probability Distribution Functions will be computed and hallmarks of intermittency will be searched. For the time intervals when intermittency is detected the analysis will move one step forward and multifractal methods will be applied as well as a wavelet analysis in order to quantify more quantitatively the local measure of the intermittency and its scaling. The results will be catalogued.

Power Spectral Density analysis of solar wind turbulence at solar maximum and minimum

The first step of the analysis, the evaluation of the Power Spectral Densities (PDFs) has been accomplished in 2013. The results are summarized in a report that can be found below:

Report on solar wind Power Spectral Densities (PSDs) computed from Ulysses, Cluster and Venus Express observations of the solar wind (1997-1998, 2000-2001, 2007-2008).

The satellite data and the corresponding spectra (images and electronic files) included in the report are available from the STORM catalog ftp repository. The access is password protected. Access is granted by request to the project coordinator ( This email address is being protected from spambots. You need JavaScript enabled to view it. ). A summary of PSD spectra recorded in the solar wind by Venus Express during solar minimum, in 2007, is inserted below (from Teodorescu et al., 2015):

PSD of B2 from Venus Express, 2007-2008; PSD from high-speed streams intervals are also highlighted.

Probability Distribution Functions analysis of solar wind intermittency at solar maximum and minimum

We performed a higher order analysis of the selected data sets in order to provide additional information about the spatio-temporal scales relevant for the turbulent fluctuations for which we already computed the spectral properties. We computed the Probability Distribution Functions of magnetic field fluctuations (an example of PDFs computed for Ulysses magnetic field data is shown below), and in some cases of velocity fluctuations. We also evaluate some of the higher order moments (flatness) in order to estimate the intermittent features of solar wind turbulence and their scaling properties.

PDF Ulysses examp

The procedure to compute the PDFs and the structure of the catalogues are described in the document inserted below:

Report on solar wind Probability Distribution Functions (PDFs) computed from Ulysses, Cluster and Venus Express observations of the solar wind (1997-1998, 2000-2001, 2007-2008).

Multifractal  analysis of solar wind intermittency at solar maximum and minimum

In order to provide additional information about the nature of the scaling of the turbulent fluctuations, for which we already computed the spectral properties and probability distribution functions, we have determined the multifractal spectra of the selected data sets. We adopt and apply two complementary methods: the Partition Function technique and the Rank Order Multifractal Analysis (ROMA), illustrated schematically by the diagrams inserted below.

Diagram illustrating the main steps of the Partition Function multifractal analysis.