A laboratory study of baroclinic chaos on the f-plane

Laboratory experiments on the transition to chaos in a two-layer rotating fluid are described. The topography of the upper and lower bounding surfaces, and the rotation rate of the apparatus, are chosen so that the f-plane case of uniform basic potential vorticity in each layer is reproduced. Experiments are carried out in the near-critical single-wave region of parameter space where previous theory suggests a snap-through bifurcation from steady baroclinic waves to chaos. Instead, as the friction parameter is decreased past the curve of neutral stability of the axisymmetric basic state, we find several bifurcations before chaos is observed. The transition scenario includes successive limit cycles of doubled periods between the steady-wave and chaotic regions of parameter space. There is also evidence of ageostrophic behavior, even when the system Rossby number is less than 0.1.