GENERATING JOVIAN-LIKE ZONAL JETS IN A RAPIDLY ROTATING FLUID EXPERIMENT

Using a large-scale rotating fluid experiment, we report the formation of strong zonal jets due to topographical effects in rotating turbulence. For the first time, we reach the so-called “zonostrophic” regime, thought to be relevant to Jupiter atmosphere for example. The jets dominate the small-scale turbulent fluctuations in amplitude and appear very stable and long-lived. Although their size is consistent with the so-called Rhines scale, we observe interesting dynamics over very long time-scales such as merging events where the number of jets decreases and their amplitude increases. These first results open new perspectives in the study of large-scale zonal flows in the laboratory. For our experimental set up (see figure 1(c)), we use a cylindrical container 1.4 meter high with an internal radius of 0.5 meter filled with up to 400 liters of water and mounted on a rotating table. The depth of the fluid layer at rest is h0 = 50cm and the rotation rate of the table is 75 RPM. This leads to a very large deformation of the fluid layer (topographic β-effect), with a minimum depth after the spin-up phase of h = 20cm at the center of the container and a maximum depth of on the side boundary of h = 88cm. A turbulent small-scale flow is driven via a basal injection/suction system made of a square tiled set of 64 inlet/outlet ports, generating velocities in the range U ≈ 1− 5 cm/s (corresponding to a Reynolds number 2.5× 10 < Re < 1.3× 10 and a Rossby number 3.3 × 10−3 < Ro < 1.6 × 10−2). Lagrangian surface velocities are measured using a Particle Tracking method using small floating particles with a typical diameter of 5 mm.