Incompressible and isotropic magnetohydrodynamic turbulence in plasms can bedescribed by an exact relation for the energy flux through the scales. ThisYaglom-like scaling law has been recently observed in the solar wind above thesolar poles observed by the Ulysses spacecraft, where the turbulence is in anAlfv\'enic state. An analogous phenomenological scaling law, suitably modifiedto take into account compressible fluctuations, is observed more frequently inthe same dataset. Large scale density fluctuations, despite their lowamplitude, play thus a crucial role in the basic scaling properties ofturbulence. The turbulent cascade rate in the compressive case can moreoversupply the energy dissipation needed to account for the local heating of thenon-adiabatic solar wind.
展开▼
