Quasi-two-dimensional decaying turbulence subject to the β effect

Abstract

Freely decaying quasi-2D turbulence under the influence of a meridional variation of the Coriolis parameter f (β effect) is experimentally and numerically modelled. The experimental flow is generated in a rotating electromagnetic cell where the variation of f is approximated by a nearly equivalent topographical effect. In the presence of a high β effect, the initial disordered vorticity field evolves to form a weak polar anticyclonic circulation surrounded by a cyclonic zonal jet demonstrating the preferential transfer of energy towards zonal motions. In agreement with theoretical predictions, the energy spectrum becomes peaked near the Rhines wave number with a steep fall-off beyond, indicating the presence of a soft barrier to the energy transfer towards larger scales. DNS substantially confirmed the experimental observations.

Keywords:

• β-plane turbulence
• Rhines scale
• zonal jets

Acknowledgment

GFC acknowledges support from the National Science Foundation (grants OCE 07-26482 and 05-25776), the Ministero dell'Università e della Ricerca Scientifica-MIUR (D.M. 26.01.01 no. 13). Thanks to P. Orlandi for providing the code that was the basis of the numerical simulations. This work has been presented at the Euromech Colloquium Particle-laden Flow. From Geophysical to Kolmogorov Scales, 21–23 June 2006, University of Twente, The Netherlands.