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7 A Natural Wind Tunnel

The solar wind has been used as a wind tunnel by L.F. Burlaga who, at the beginning of the ’90s, started to investigate anomalous fluctuations (Burlaga, 1991aJump To The Next Citation Point,bJump To The Next Citation Point,cJump To The Next Citation Point1995) as observed by measurements in the outer heliosphere by the Voyager spacecraft. In 1991 E. Marsch, in a review on solar wind turbulence given at the Solar Wind Seven conference (Marsch, 1992Jump To The Next Citation Point), underlined the importance of investigating scaling laws in the solar wind and we like to report his sentence: “The recent work by Burlaga (1991aJump To The Next Citation Point,bJump To The Next Citation Point) opens in my mind a very promising avenue to analyze and understand solar wind turbulence from a new theoretical vantage point. …This approach may also be useful for MHD turbulence. Possible connections between intermittent turbulence and deterministic chaos have recently been investigated …We are still waiting for applications of these modern concepts of chaos theory to solar wind MHD fluctuations.” (cf. Marsch, 1992, page 503). A few years later Carbone (1993Jump To The Next Citation Point) and, independently, Biskamp (1993) faced the question of anomalous scaling from a theoretical point of view. More than ten years later the investigation of statistical mechanics of MHD turbulence from one side, and of low-frequency solar wind turbulence on the other side, has produced a lot of papers, and is now mature enough to be tentatively presented in a more organic way.


 7.1 Scaling exponents of structure functions
 7.2 Probability density functions and self-similarity of fluctuations
 7.3 What is intermittent in the solar wind turbulence? The multifractal approach
 7.4 Fragmentation models for the energy transfer rate
 7.5 A model for the departure from self-similarity
 7.6 Intermittency properties recovered via a shell model

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