Anisotropic turbulence and Rossby waves in an easterly jet: An experimental study

A westward propagating jet is investigated experimentally. The focus is on complex interaction between anisotropic turbulence with inverse energy cascade and Rossby waves. The energy spectrum is highly anisotropic. To diagnose turbulence characteristics, we explore the analogy between turbulent overturns in stably stratified and quasi-geostrophic flows and develop a novel method based upon the monotonizing of potential vorticity (PV). The RMS displacement from the monotonic PV profile yields a length scale, L-M, analogous to the Thorpe's scale used in flows with stable stratification. As the Thorpe scale is proportional to the Ozmidov scale, the scale L-M is proportional to the scale L at which the time scales of turbulent overturns and Rossby waves are approximately equal. The relationship between L-M and L is established here for the first time. The method of PV monotonizing offers a simple and powerful tool for diagnosing geophysical and planetary macroturbulence.