The role of magnetic field in solar wind turbulent cascade

The Yaglom law for the mixt third order moment of the Elsasser fields fluctuations has been recently observed in the solar wind. This observation confirm the existence of a MHD turbulent cascade in the interplanetary plasma, in both ecliptic and polar wind. In the polar wind measured by Ulysses spacecraft, the cascade occasionally holds up to scales of days. The nature of such cascade, and in particular the role of magnetic field at large scales, are discussed. The different possible scenaries show that solar wind turbulent cascade is not universal.