ANISOTROPIC DIFFUSION AND SHEAR INSTABILITIES

We examine the role of anisotropic turbulence on the shear instabiliti es in a stratified flow. Such turbulence is expected to occur in the r adiative interiors of stars, due to their differential rotation and th eir strong stratification, and the turbulent transport associated with it will be much stronger in the horizontal than in the vertical direc tion. It will thus weaken the restoring force which is caused by the g radient of mean molecular weight (mu). We find that the critical shear which is able to overcome the mu-gradient is substantially reduced by this anisotropic turbulence, and we derive an estimate for the result ing turbulent diffusivity in the vertical direction.