Nonlinearities and currents in rotating turbulence

Rotating turbulent flows are common in geophysical systems and are not fully understood. I will present a set of experiments in turbulence within a rapidly rotating water tank. We find that the steady flow within a horizontal plane develops over long times via inverse energy cascade. Simultaneously, a 3D field of inertial waves develops a continuous energy spectrum with a robust scaling. We are focused on the interplay between the wave field and the quasi- 2D turbulent field. Specifically, we try to identify the dominant energy transfer processes in the flow.

Using a short perturbation to a steady energy injection rate, we generate a "probe pulse" with which we examine energy currents in the frequency, wavenumber and real spaces. We find a non-local, energy transfer from high to low frequencies, which reflects a transition from 3D to quasi-2D waves. Over longer times, we observe the inverse cascade of the energy injected by the perturbation. Surprisingly, this process, which lasts ~100 system's turn over times, occurs while the modes propagate as inertial waves. This observation, as well as data from direct separation of the flow to "waves" and "2D" components, suggest that such sharp separation is questionable when considering flows in finite volumes.