Turbulence modeling approach to astrophysical flow phenomena

Abstract

Vigorous nonlinearity represented by huge Reynolds numbers and strong inhomogeneities of large-scale fields such as velocity shear, non-uniform magnetic field, density variation, etc. are very ubiquitous properties of astrophysical turbulent flows. Turbulence modeling approach provides a very strong tool for analyzing such nonlinear and inhomogeneous flows. In addition to the mutual interaction between the mean and fluctuation, as is present in the usual hydrodynamic turbulent flows, there are some features in the astrophysical ones. A prominent feature may be the dynamics between the turbulent transport enhancement and suppression due to symmetry breakage arising from rotation, magnetic field, etc. In order to treat astrophysical flows properly, such features should be incorporated into the astrophysical turbulence models. Some illustrative applications of turbulence models to the astrophysical phenomena are discussed, which include solar winds, magnetic reconnection, and solar-activity cycle.