Surface wind mixing in the Regional Ocean Modeling System (ROMS)

Abstract

Mixing at the ocean surface is key for atmosphere-ocean interactions and the distribution of heat, energy, and gases in the upper ocean. Winds are the primary force for surface mixing. To properly simulate upper ocean dynamics and the flux of these quantities within the upper ocean, models must reproduce mixing in the upper ocean. To evaluate the performance of the Regional Ocean Modeling System (ROMS) in replicating the surface mixing, the results of four different vertical mixing parameterizations were compared against observations, using the surface mixed layer depth, the temperature fields, and observed diffusivities for comparisons. The vertical mixing parameterizations investigated were Mellor-Yamada 2.5 level turbulent closure (MY), Large-McWilliams-Doney Kpp (LMD), Nakanishi-Niino (NN), and the generic length scale (GLS) schemes. This was done for one temperate site in deep water in the Eastern Pacific and three shallow water sites in the Baltic Sea. The model reproduced the surface mixed layer depth reasonably well for all sites; however, the temperature fields were reproduced well for the deep site, but not for the shallow Baltic Sea sites. In the Baltic Sea, the models overmixed the water column after a few days. Vertical temperature diffusivities were higher than those observed and did not show the temporal fluctuations present in the observations. The best performance was by NN and MY; however, MY became unstable in two of the shallow simulations with high winds. The performance of GLS nearly as good as NN and MY. LMD had the poorest performance as it generated temperature diffusivities that were too high and induced too much mixing. Further observational comparisons are needed to evaluate the effects of different stratification and wind conditions and the limitations on the vertical mixing parameterizations.

Nonlinearly interacting entrainment due to shear and convection in the surface ocean

“…The mixing parameterization schemes tested in this study were the KPP scheme 6 , level 2.5 MY scheme 5 , 40 , 41 , and level 2.5 Nakanishi–Niino (NN) scheme 42 – 44 . The NN scheme is a modified version of the MY scheme and is used in ocean models 45 as well as atmospheric models 46 , 47 . The boundary and initial conditions were the same as those in the LES.…”

Delivering Sustained, Coordinated, and Integrated Observations of the Southern Ocean for Global Impact

“…Presently, vertical mixing for all these mechanisms is parameterized in ocean and climate models. Some of the parameterizations reproduce the wind-generated upper mixedlayer depth well, whereas others overmix the water column (Robertson and Hartlipp, 2017). Likewise, with a resolution of 1 km or finer, internal tides and tidal mixing can be replicated by some parameterizations (Robertson, 2006).…”

Impact of Satellite Wind on Improving Simulation of the Upper Ocean Response to Tropical Cyclones

“…Where 𝑘 represents the turbulent kinetic energy, 𝑙 represents the dissipation scale, 𝜀 denotes dissipation, 𝜔 represents the inverse turbulent time scale. The 𝑘 − 𝜔 model was adopted to calculate the vertical viscosity and diffusion terms, which is well-suited for 3D computations with a coarse vertical resolution of the mixed layer [56,57].…”