SEMINAR: MPO Seminar: Dr. Boris Galperin, Friday, October 15, at 2:00 p.m., Slab Conference room, S/A 103

[Sandrine Apelbaum <sapelbaum@rsmas.miami.edu>]

MPO Seminar

Dr. Boris Galperin

University of South Florida

 "Zonostrophic turbulence, zonal jets and the mixing barriers"

Room: Slab Seminar Room S/A 103

Date: Friday,October 15, 2:00 p.m.

Abstract

Two-dimensional (2D) turbulent flows with a b-effect, small-scale forcing and a large-scale drag feature anisotropic inverse energy cascade that may lead to a development of slowly varying systems of alternating zonal jets. The anisotropization of scalar transport in meridional and zonal directions has been well documented but in some studies, the boundaries between the jets are associated with mixing barriers that tend to suppress the meridional transport. We study the meridional scalar transport using numerical simulations of barotropic 2D turbulence on the surface of a rotating sphere in the zonostrophic regime. We found that when the small-scale forcing is present, the meridional diffusivity, D_y , never goes to zero but is determined by b and e, the rate of the inverse cascade. When e and the large-scale drag are suddenly removed, the flow undergoes rapid reorganization with energy flowing to large-scale, low wave number modes at the expense of small-scale modes. The jet structure does not change significantly but D_y is greatly reduced. Trying to understand the dependence of D_y on both b and e, we conducted studies of lateral diffusion in forced and unforced turbulent flows on a non-rotating sphere. In this case, the flow was isotropic and turning off the forcing did not have much effect on D_y . Since the low wave number, near-zonal modes in rotating flows are dominated by Rossby waves, we concluded that these waves play a major role in determining D_y in unforced flows via limiting the meridional excursions of fluid particles. This effect is sometimes referred to as the Rossby wave elasticity. We developed a simple heuristic model to elucidate this result. An analogy can be drawn between this result and the diapycnal diffusion in turbulent flows with strong stable stratification.

Sandrine Apelbaum

Meteorology and Physical Oceanography 
Rosenstiel School of Marine and Atmospheric Science
University of Miami
4600 Rickenbacker Causeway
Miami, FL 33149-1098
Tel     (305) 421-4057
Fax     (305) 421-4696

sapelbaum@rsmas.miami.edu