STORM

"Solar system plasma Turbulence: Observations, inteRmittency and Multifractals"

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 Obiettivo del progetto (Objective)

'In this project we investigate solar system plasma turbulence from in-situ data gathered by automated platforms launched by the European Space Agency (ESA) and NASA. We investigate how the features of turbulence and intermittency vary with the solar activity and estimate the corresponding impact. We use electromagnetic field and plasma data provided by a core of three ESA spacecraft, Ulysses, Venus Express and the Cluster quartet, in coherence with data from other missions like ESA's Giotto and Rosetta, NASA's THEMIS, Cassini and Mars Global Surveyor. Complementary to the satellite databases we study the fluctuations of the geomagnetic field observed on ground. A package of advanced nonlinear analysis methods will be applied on the selected data sets. Power Spectral Densities (PSD) and Probability Distribution Functions (PDF) will be computed first. In a next step we apply five higher-order methods of analysis: (i) the partition function multifractal analysis, (ii) the Rank Ordered Multifractal analysis, (iii) the wave telescope, (iv) the multi-spacecraft methods for anisotropy (v) the discriminating statistics. The targeted physical processes are: the turbulent transfer of energy and dissipation, the intermittency and multifractals, the anisotropy, and non-linearity of the solar system plasma turbulence. The Consortium includes European experts with valuable achievements in space plasma turbulence and complexity, as well as in satellite data analysis. The members of the Consortium are principal or co-investigators of several experiments on-board the selected missions. Two American experts agreed to collaborate and will increase the links with major space actors like the USA. The project responds to the Objectives of the Call by its international, multi-disciplinary dimension, the large number of targeted space missions and databases and the associated analysis methods, and the ambitious scientific objectives that are expected to have a significant impact.'

Introduzione (Teaser)

Solar wind and planetary magnetospheres are certainly the most accessible astrophysical plasmas to in situ measurements. Using recent satellites as a space microscope, scientists zoom in on solar system plasmas to reveal the finest detail.

Descrizione progetto (Article)

Solar wind and planetary plasmascan be described by magnetohydrodynamics(MHD) at large scales, where energy is transferred from larger to smaller scales and particle kinetics at the smallest scales. This complex description should include dissipative processes. The question of how turbulence develops and terminates the energy cascade and how the energy is partitioned between scales is among the objectives of the EU-funded project 'Solar system plasma turbulence: Observations, intermittency and multifractals' (http://www.storm-fp7.eu/ (STORM)).

The answer is fundamental to understanding processes of particle acceleration and plasma heating in solar wind and other astrophysical plasmas. Ulysses' observations as well as recent planetary spacecraft measurements brought important insights into fluctuations of fields that describe the plasma state. Scientists used multiple approaches to analyse the properties of turbulence in various regions of the solar system, like the solar wind and the planetary magnetospheres of Venus, Earth and Saturn.

Observations from Cluster, Venus Express, Giotto and Cassini satellites offered the chance to identify and characterise plasma structures at the interface of planetary magnetospheres and solar wind. Moreover, their high time resolution measurements of plasma and magnetic field made it possible to probe the smallest scales ever explored in solar wind and test advanced models based on a statistical approach, like e.g. the (multi)fractal geometry.

One of the main outcomes of the STORM project is a software library for non-linear data analysis that gathers methods able to reveal the structure of turbulence. The library includes methods from lower-order analysis, like the power spectral density analysis, to higher-order analyses, like the probability distribution functions and multi fractals. The library can be used to effectively analyze specific turbulent data intervals carefully selected within the STORM project, however, it is versatile enough to ingest data from different space missions.

Like its neutral fluid counterpart, astrophysical turbulence remains poorly understood but is an important issue as it mediates fundamental dynamic coupling between large and small scales in an ubiquitous natural phenomenon. Scientific results gained in the STORM project contribute to draw a more complete picture of the phenomenology of turbulence in space plasmas.

New information provided about turbulence in solar wind and planetary plasmas will open up new ways of looking at space weather and the unstable behaviour of plasma that affects the operation of fusion power plants.