LARGE-SCALE VORTICES IN ROTATING STRATIFIED DISKS

A very new possibility of generation of large-scale flow patterns in t urbulent astrophysical bodies is discussed. When the global rotation a nd 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'' solu tion of the Reynolds equation is found in a further analogy to the hyd romagnetic dynamo. The numerical solution of a 1D eigenvalue problem l eads to a rather low critical ''dynamo number'' (congruent-to 6) imply ing that the new mean-flow excitation can indeed act in rotating and s tratified astrophysical disks (and spheres?).