On the stirring properties of the thermally-driven rotating annulus

•The stirring properties of the thermally driven rotating annulus are investigated.•The finite scale Lyapunov exponent (FSLE) is applied to the flow.•The FSLE correctly identifies barriers between different flow regions.•The Eulerian symmetry measure (ESM) is applied to the flow.•The ESM more efficiently identifies some stirring properties of the flow.

The stirring properties of the thermally-driven rotating annulus have not been extensively studied, despite sustained interest in the stirring properties of various geophysical flows, and the wide applicability of the rotating annulus to geophysical problems. This paper takes important steps towards a thorough investigation of the stirring properties of thermally-driven rotating annulus flows, by demonstrating numerically the utility of two stirring measures for a parameter set yielding relatively simple flow conditions. The first measure is the finite scale Lyapunov exponent (FSLE), which has been successfully used to highlight the stirring properties of various geophysical flows. The second measure is the Eulerian symmetry measure, which has been far less widely used: this second measure does not provide such a detailed view of the stirring properties as the FSLE, but is far more efficient to calculate. Both measures are shown to have some success for the simple flow case studied, providing a strong foundation for further investigation into more complicated flows.