Appears in collection : 2026 - T2 - WS1 - Vortices and vorticity in geophysical flows

Some tropical cyclones develop a calm, cloud-free eye at their center, but the minimal physical ingredients required for its formation remain debated. Here we report the experimental observation of eye formation in an idealized dry cyclone produced by rotating turbulent convection. A constant heat flux is imposed at the bottom of a large-aspect-ratio cylindrical cavity filled with air, while the outer boundary is maintained at a fixed temperature. This forcing drives a large-scale radial circulation with rising flow at the center. As the system is set into rotation and the rotation rate is increased, the Coriolis force first organizes the flow into a large-scale turbulent cyclone, before stronger rotation leads to quasi-geostrophic small-scale convection. Within the cyclone regime, particle image velocimetry in a vertical plane containing the rotation axis reveals, within a well-defined region of parameter space, a small central recirculation with persistent axial subsidence has strong similarities with a cyclone eye. The eye appears below a Rossby number of about 3.5, revealing the balance between convective driving and rotation required for its formation. These experiments demonstrate, in a fully three-dimensional turbulent configuration, that rotation and Boussinesq convection alone are sufficient to produce a cyclone eye, without invoking atmospheric complexity such as moisture or compressibility.