Flow measurements of turbulent rotating Rayleigh-Bénard convection in the geostrophic regime*

Rotating turbulent convection can be used as a simple model that captures principal properties of many large-scale geophysical and astrophysical flows. In particular the rotation-dominated geostrophic regime is relevant here. It is named after the so-called geostrophic force balance of pressure gradient and Coriolis forces, which dictates the flow dynamics in this regime to lowest order. Dedicated experiments and numerical simulations have recently been able to enter this regime. Here we present a suite of flow measurements in geostrophic convection. Stereoscopic particle image velocimetry is applied to measure three-component velocity fields in a horizontal planar cross-section of a large-scale cylindrical convection experiment. We consider the magnitude of velocity and vorticity fluctuations at different Rayleigh numbers (strength of thermal forcing) under constant, rapid rotation and interpret them according to scaling predictions based on theoretical force balances. Energy spectra and flow animations reveal the development of a quadrupolar vortex structure that fills the entire cross-section.