Letter to the Editor Mean electromotive force and dynamo action in a turbulent flow

We derive the expression for the mean electromotive force in a turbulent flow taking into account stretching of turbulent magnetic field lines and streamlines by the mean flow. Shear stresses break the symmetry of turbulence in such a way that turbulent motions become suitable for the dynamo action. The contribution of this effect to themean electromotive force is proportional to the production of spatial derivatives of the mean magnetic field and themean velocity thus it cannot be described, in principle, in terms of the conventional alpha-effect.