Laboratory-scale experimental modeling of superrotating planetary atmospheres

Laboratory experiments constructed following the principle of hydrodynamic similarity often prove to be surprisingly accurate models of large-scale atmospheric flow phenomena. In the von Kármán Laboratory of Environmental Flows we designed new innovative experiment configurations, which are modified versions of the water-filled differentially heated rotating annulus setting, a widely used laboratory-scale minimal model of the mid-latitude Terrestrial atmospheric circulation. In the framework of our ESA-sponsored VERATAC (Venus Radar Topography and Atmospheric Circulation) project and in preparation for ESA's EnVision mission to Venus, we intend to model the hydrodynamic instabilities emerging in the superrotating upper atmosphere of the planet Venus, where the cloud tops circle the planet ca. 60 times faster than the rotation period of the surface. In our preliminary experiments and numerical simulations, we have explored the character of the atmospheric flow patterns developing at different values of the radial temperature gradient and rotation rate, while also applying an azimuthally (zonally) inhomogeneous, dipole-like heating and cooling along the rim of the cylindrical tank. These boundary conditions imitate the thermal driving provided by the meridional temperature contrast – yielding an Eady cell-like overturning convection on Venus – and the thermal difference between the day side and night side, both of which are essential conditions for superrotation to occur. Besides the better understanding of the Venusian atmosphere, this experimental configuration may also be a useful model of the large-scale atmospheric circulation of tidally locked exoplanets, on which a large pool of new empirical data is expected to become available in the coming decade from new space observatories.