Cross-helicity turbulence model: Application to MHD phenomena from solar convection zone to heliosphere

Cross helicity (velocity-magnetic field correlation) is expected to play a key role in several geo/astrophysical processes including dynamo action, suppression of turbulent transport, etc. We discuss the relevance of the cross-helicity effects with the aid of the turbulence model. A turbulence model with the cross-helicity effects incorporated may be called the “cross-helicity turbulence model”. This model is applied to several MHD phenomena ranging from the formations of magnetic fields and plasma motions in the solar convection zone to the solar-wind evolution in the heliosphere. Generation of turbulence quantities depends on the inhomogeneity of large-scale fields, and turbulence in turn determines the configuration of the mean fields through the turbulent transport. Such nonlinear interactions between the mean- and fluctuation-fields are explored with the aid of numerical simulations with cross-helicity turbulence model. Through the comparisons to the observation, validity of the turbulence model is examined. Examinations include (i) A large-eddy simulation of the sunspot flow reveals how and how much cross helicity is generated there; (ii) A eddy-viscosity-type turbulence model shows how the turbulence quantities evolves under the influence of the large-scale velocity and magnetic-field shears.