Compressible turbulence in space and astrophysical plasmas : Analytical approach and in-situ data analysis for the solar wind

Abstract : My thesis work is principally dedicated in understanding the role of compressibility in lowfrequency turbulence of space plasmas (the solar wind, magnetospheric plasma etc.) and astrophysical plasmas (interstellar molecular cloud, the core of a star etc.). Three new exact relations have been derived analytically in the framework of isothermal and polytropic hydrodynamic turbulence and also for an isothermal MHD plasma. By using these relations, various universal scalingproperties of compressible turbulence have been investigated. In addition, plausible phenomenologieshave been proposed in order to theoretically reproduce different power laws for energy power spectra which had been obtained in previous numerical simulations of compressible turbulence. A semi-qualitativedistinction between sub-sonic and supersonic regime of turbulence is hence concluded. In the second part, an analysis using THEMIS spacecraft data is also performed in a view to explainingthe effect of the compressibility in the turbulence of the fast solar wind. A remarkable smooth scalingin comparison with incompressible law is obtained for several intervals of fast solar wind. The corresponding turbulent energy flux is also found to be sufficient to explain the anomalous heating of fast solar wind.
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Supratik Banerjee. Compressible turbulence in space and astrophysical plasmas : Analytical approach and in-situ data analysis for the solar wind. Solar and Stellar Astrophysics [astro-ph.SR]. Université Paris Sud - Paris XI, 2014. English. ⟨NNT : 2014PA112206⟩. ⟨tel-01087024⟩

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