Turbulent dynamo action in a shear flow

We consider the mean electromotive force and a dynamo-generated magnetic fi eld, taking into account the stretching of turbulent magnetic field lines b y a shear flow. Calculations are performed by making use of the second-orde r correlation approximation. In the presence of shear, the mirror symmetry of turbulence can be broken; thus turbulent motions become suitable for the generation of a large-scale magnetic field. Regardless of the shear law, t urbulence can lead to a rapid amplification of the mean magnetic field. The growth rate of the mean magnetic field depends on the length-scale: it is faster for the fields with smaller length-scale. The mechanism considered i s qualitatively different from the alpha dynamo, and can generate only a ma gnetic field that is inhomogeneous in the direction of flow. In contrast to the alpha dynamo, this mechanism also allows the generation of two-dimensi onal fields. The suggested mechanism may play an important role in the gene ration of magnetic fields in accretion discs, galaxies and jets.