3 Early Observations of MHD Turbulence in the Ecliptic

Here we briefly present the history, since the first Mariner missions during the ’60s, of the main steps towards the completion of an observational picture of turbulence in interplanetary space. This retrospective look at all the advances made in this field shows that space flights allowed us to discover a very large laboratory in space. As a matter of fact, in a wind tunnel we deal with characteristic dimensions of the order of $L < 10 m$ and probes of the size of about $d -~ 1 cm$ . In space, $L -~ 108 m$ , while “probes” (say spacecrafts) are about $d - ~ 5 m$ . We have a much larger laboratory but, up to now, we have made only single point measurements although the magnetospheric ESA-Cluster project has shown all the advantages of performing 3D measurements in space.

3.1 Turbulence in the ecliptic
  3.1.1 Spectral properties
  3.1.2 Evidence for non-linear interactions
  3.1.3 Fluctuations anisotropy
  3.1.4 Simulations of anisotropic MHD
  3.1.5 Fluctuations correlation length and the Maltese Cross
  3.1.6 Magnetic helicity
  3.1.7 Alfvénic correlations as uncompressive turbulence
  3.1.8 Radial evolution of Alfvénic turbulence
3.2 Turbulence studied via Elsässer variables
  3.2.1 Ecliptic scenario
  3.2.2 On the nature of Alfvénic fluctuations