Dependence of Submesoscale Eddy Distortion on Turbulent Mixing Schemes and It Effect on Boundary Layer Turbulence
Abstract
Different effect of the 6 OBL mixing models on the distortion of a submesoscale eddy and the corresponding responses of mixed layer dynamics are studied using stationary eddy experiments with NCOM and HYCOM. Generally, for the second moment turbulent closure models, the eddy mixed layer depth (MLD) is deeper in the Mellor-Yamada level 2.0 and 2.5 schemes but weakens much more quickly. The Ramsey-Harcourt and Kantha-Clayson schemes result in an eddy that is stronger and more coherent while characterized by a shallower mixed layer. In comparison to the second moment turbulent closure scheme, the KPP scheme produces weaker turbulent mixing with more symmetric structures and thus helps to better maintain the strength and coherence of the eddy.The effect of submesoscale eddies on oceanic boundary layer turbulence was investigated through controlled numerical experiments conducted using the NCOM, HYCOM and the NCAR LES model with a moving eddy. The mixed layer dynamics and the variation of the MLD are very different at different locations relative to the eddy and between the HYCOM and LES simulations. Distinct dynamical processes are identified at different locations in the LES simulations. Along the center of the eddy, the turbulent field is dominated by strong shear production due to the geostrophic currents associated with the eddy, and the strong turbulent velocity fluctuations induced by the large horizontal shear brought by the eddy further act on the mean vertical shear to enhance the TKE and vertical mixing. On both sides of the eddy, the mixed layer dynamics are dominated by the combined effect of Ekman buoyancy flux and geostrophic shear.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 03, 2021
- Accession Number
- AD1154396
Entities
People
- Adam Rydbeck
- Prasad G. Thoppil
- Yalin Fan
Organizations
- United States Naval Research Laboratory