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, 1991a
,b,c, 1995) 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, 1992), underlined the importance of investigating
scaling laws in the solar wind and we like to report his sentence: “The recent work by Burlaga (1991a,b)
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 (1993)
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.
