Flow instabilities in a microgravity model of differentially rotating planetary atmospheres

Gas giant planets in the Solar System exhibit differential rotation, thus zonal wind speeds at different planetographic latitudes can be markedly different. Along boundaries between such zonal domains wavy flow instabilities can develop. Based on the principle of hydrodynamic similarity, many large-scale atmospheric phenomena can be modeled in conceptual fluid dynamics experiments in Earth-based laboratories. However, shear instabilities arising due to the differential rotation of a free spherical fluid surface are not possible to capture in experimental setups under normal gravity conditions. We report on the results of fluid dynamics experiments in microgravity performed on board the International Space Station. A spherical water layer is put into rotation around its center via a manually driven platform imposing boundary conditions for differential rotation on the working fluid. The equatorial domain of the fluid has a higher rotation rate around the axis than its polar section. Using Particle Image Velocimetry (PIV) we explore the flow field developing at various angular velocities, and the barotropic instability emerging in the the shear region. The empirical findings regarding the most unstable wavenumbers may be applicable to the atmospheric circulation of gas giant planets.