Thermal Waves in a Venus-Inspired Rotating Annulus Experiment

Large-scale, slowly propagating wave-like structures have been observed in the atmosphere of Venus, but their dynamical origin remains uncertain. In laboratory experiments we investigated whether analogous structures can develop through baroclinic instability under conditions imitating the Venusian lower-to-middle cloud region. A differentially heated rotating annulus set-up was designed to conceptually imitate the planetary setting in terms of the relevant geometrical and dynamical similarity parameters, applying meridional and zonal temperature contrast as thermal forcing. Temperature time series analysis, infrared thermography, and feature tracking velocimetry were used to characterize the flow in the system. Slowly propagating, billow-like patterns were observed, similar in shape to the vortices of Venus. Wave activity was found to emerge above a critical meridional temperature contrast, but became substantially reduced when the ratio of the imposed zonal and meridional temperature contrasts exceeded approximately 1.6. The experiments indicate that the relative magnitude of meridional and day-night thermal forcing may play an important role in determining the occurrence of such wave-like atmospheric structures.