Progress in Characterizing the Route to Geostrophic Turbulence and Redesigning Thermally Driven Rotating Annulus Experiments

In this paper we calculate Lyapunov exponents and adapt a diagnostic tool, originally used for another purpose by Lorenz (1969), to characterize the degree and nature of the chaotic behavior observed in a thermally driven rotating fluid annulus at different points in parameter space as a control parameter (the rotation rate) is varied over a significantly wide range. We also report on our initial progress toward making the annulus experiments more relevant to the behavior of baroclinic waves in Earth's atmosphere. Owing to the existence of a background potential vorticity gradient, baroclinic waves in the atmosphere propagate both meridionally and vertically and are not trapped as they are in conventional annulus experiments. Our approach involves the redesign of such experiments through the application of radiational heating from above to provide a background potential vorticity gradient on which baroclinic waves can travel. These experiments are in their earliest stage of design and implementation. If successful, they promise to provide a new paradigm for future experiments with thermally driven rotating fluids.