SYMMETRY, SIDEWALLS, AND THE TRANSITION TO CHAOS IN BAROCLINIC SYSTEMS

A high-resolution, quasi-geostrophic numerical model is utilized to ex amine two-layer baroclinic flow in a cylinder. Particular attention is given to the role of horizontal shear of the basic state induced by v iscosity near the cylinder wall, and to the desymmetrization brought a bout by the cylindrical geometry, in the transition to baroclinic chao s. Solutions are computed for both f-plane and beta-plane situations, and the results are compared to previous laboratory experiments. Agree ment in the former case is found to be good, although the onset of cha os occurs at slightly lower forcing in the laboratory when its basic f low is prograde, and at higher forcing amplitude when the experimental basic azimuthal currents are retrograde. This suggests that the modes t discrepancies may be attributable to computationally neglected ageos trophic effects in the interior fluid and Ekman boundary layers. When beta not equal 0, the numerical and laboratory results are in excellen t agreement. The computational simulations indicate that the viscous s idewall boundary layer plays a pivotal role in the dynamics. Moreover, in contrast to previous studies performed in a periodic, rectilinear channel, the route to chaos is largely temporal and involves relativel y few spatial modes. The reduction in symmetries upon going from f-pla ne channel to either f-plane or beta-plane cylinder models leads to fe wer secondary instabilities and fewer spatial modes that are active in the dynamics.