LARGE-SCALE VORTICES IN ROTATING STRATIFIED DISKS

A very new possibility of generation of large-scale flow patterns in turbulent astrophysical bodies is discussed. When the global rotation and the fluid stratification are simultaneously involved, the Reynolds stress tensor contains contributions linear in the mean velocity. Then for sufficiently rapid rotation the system becomes unstable to large-scale motions. The mean velocity equation is very similar to the mean magnetic field equation of dynamo theory. A plane ''dynamo-wave'' solution of the Reynolds equation is found in a further analogy to the hydromagnetic dynamo. The numerical solution of a 1D eigenvalue problem leads to a rather low critical ''dynamo number'' (congruent-to 6) implying that the new mean-flow excitation can indeed act in rotating and stratified astrophysical disks (and spheres?).