Rainer Hollerbach, Eun-jin Kim

Magnetic fields and shear flows play an important role in many systems including astrophysical, geophysical and laboratory plasmas. We report how the growth of magnetic fields is modified by large-scale shear flow by investigating a kinematic dynamo in a spherical shell of highly conducting fluid surrounded by an insulator. A small scale prescribed velocity field is taken to be axisymmetric, steady and strongly helical. Small-scale flow is chosen in such a way it allows the dipole/quadrupole decoupling for magnetic field $B$. On the other hand, large-scale shear flows are taken to be in radial or latitudinal directions. By numerically solving induction equation with the prescribed small-scale flow and large-scale shear flow, we investigate the effects of large scale shear on dynamo for different azimuthal $m$ modes for large magnetic Reynolds number $R_m$ such as the growth rate and structures of magnetic field $B$. In all cases, the growth rate of the magnetic field is found to decrease as the strength of shear flow increases, which indicates that the dynamo is suppressed in the presence of shear.