Generation of inertia‐gravity waves in a baroclinically unstable fluid

A novel technique is used to visualize and measure the baroclinically unstable flow in a two‐layer, rotating annulus experiment with very high resolution in space and time. It is found that small‐scale, high‐frequency waves are generated in certain preferred locations within the flow by a baroclinic wave undergoing amplitude vacillation. These fast waves are investigated in terms of their dispersion relation, and are shown to be consistent with inertia‐gravity waves, generated in association with a source moving with the large‐scale baroclinic wave. The occurrence of these waves is described and discussed in the context of spontaneous adjustment radiation and the meteorological slow manifold. Phase‐portrait analyses of the present experiments indicate that, despite the apparent generation of inertia‐gravity waves as spontaneous adjustment radiation, the resulting vacillatory behaviour remains consistent with low‐dimensional dynamics.