Role of Cross-Helicity in Magnetohydrodynamic Turbulence

Strong incompressible three-dimensional magnetohydrodynamic turbulence is investigated by means of high-resolution direct numerical simulations. The simulations show that the configuration space is characterized by regions of positive and negative cross-helicity, corresponding to highly aligned or antialigned velocity and magnetic field fluctuations, even when the average cross-helicity is zero. To elucidate the role of cross-helicity, the spectra and structure of turbulence are obtained in "imbalanced" regions where cross-helicity is nonzero. When averaged over regions of positive and negative cross-helicity, the result is consistent with the simulations of balanced turbulence. An analytical explanation for the obtained results is proposed.