An application of the turbulent magnetohydrodynamic residual-energy equation model to the solar wind

Abstract

A magnetohydrodynamic (MHD) turbulence model incorporating the turbulent MHD residual energy (difference between the kinetic and magnetic energies) is applied to solar-wind turbulence. In the model, the dynamics of the turbulent cross-helicity (cross-correlation between the velocity and magnetic field) and the turbulent MHD residual energy, which are considered to describe the degree of Alfvénicity of the MHD turbulence, are solved simultaneously with the dynamics of the turbulent MHD energy and its dissipation rate. The transition of solar-wind turbulence from the Alfvén-wave-like fluctuations near the Sun in the inner heliosphere to the fully developed MHD turbulence in the outer heliosphere is discussed. Magnetic dominance in the solar-wind fluctuations is addressed from the dynamics of the evolution equation of the residual energy. An interpretation of the observed Alfvén ratio (ratio of the kinetic to magnetic energies) of ∼0.5 is proposed from the viewpoint of a stationary solution of the turbulence model.