Baroclinic Instability and Geostrophic
Turbulence Analyzed By Laboratory Experiment

The Big Table is a laboratory study to investigate the regime of turbulent geostrophic flow, which is relevant to the large-scale zonal (East-West) flows being observed in Earth's oceans. The focus will be on the ocean circulation in the Southern Ocean around Antarctica where a multiple jet regime appears to exist.

Adapted from Read et al. 1998

The archetypal situation of unconstrained, planetary-scale flow around a pole can be modeled by a rotating annulus of fluid. The "annulus" refers to the donut-shaped volume in between two concentric cylinders that rotate with the working fluid. Cooling the inner cylinder and heating the outer cylinder creates sloping density contours, which gives this region of fluid the same buoyancy forcing observed in the middle of the Southern Ocean. As far as geophysical flows are concerned, the principal effect of the fact that Earth is spherical is the Beta Effect, which is related to the way the Coriolis force changes with a curving Earth. One can mimic the Beta Effect with a change in the depth of the working fluid with radius (this is the so-called Topographic Beta Effect). With proper scaling analysis, then, flows on the spherical earth can be re-created in a cylindrical tank surprisingly well (see Hide and Mason 1975, Wordsworth et al. 2008).

A unique, large rotating table facility exists at FSU dating from the early classic baroclinic wave experiments. This facility will be used to achieve the appropriate parameter ranges.

Model of Big Table

Photo of Big Table

Original Mechanical Diagram

Support Structure of Annulus

Visualization of the flow will be carried out qualitatively with dye-release (depicting Lagrangian transport) and rheoscopic tracer (depicting Eulerian shear profiles). Quantitative measurements will be made by PIV (Particle Image Velocimetry) and PLIF (Planar Laser-Induced Fluorescence), both imaged with a high-sensitivity CCD Camera rotating with the experiment.

A numerical model involving the MITgcm will also be used to guide the exploration of these regimes.

• Kevin Speer, Principal Investigator
• Carlowen Smith, Graduate Student