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.

Zonal Jets in Rotating Shallow Water Turbulence

“…3-b). Similar results have been found in Espa et al [3,35] and in [36] in which the authors studied also the asymmetry between cyclonic/anticyclonic vortices. EM forcing in a forced regime was used in Espa et al [4] in order to study small-scale turbulence on the β-plane in a more realistic configuration, since in nature the energy is continuously supplied.…”

“…In the first reported experiments of this kind, it was found that the induced fluid velocity was proportional to the magnitude of the EM forcing [34]. EM forcing was used also to study β-plane turbulence in decaying [2,3,35,36] and forced regimes [4]. In this paper we will show results from experiments performed in a rotating electromagnetic cell.…”

“…where r m = R/2 is a mid-latitude reference point being R the maximum radial distance, s = Ω 2 /2g [2,3]. In our experiments, a turbulent flow was produced non-intrusively by means of an electromagnetic forcing.…”

“…Evidences of this phenomenon were recovered in numerical simulations [1], laboratory experiments [2][3][4] and in field measurements of giant planets' atmosphere [5]. Recent studies have revealed the presence of zonation also in the Earth's oceans; in fact, zonal jets were recovered in the outputs of Oceanic General Circulation Models-GCMs [6] and from satellite altimetry observations [7].…”

On the influence of a β‐effect on Lagrangian diffusion

“…In order to simulate flows in the northern hemisphere the rotating table rotation is counter‐clockwise. The parabolic free surface assumed by the fluid under rotation is used to model the β ‐effect in laboratory [ Afanasyev and Wells , 2005; Espa et al , 2008], in our model the point of maximum depression of the fluid surface represents the pole while the peripheral areas of the domain correspond to lower latitudes. The corresponding expression for β can be found in Espa et al [2009].…”