Parameterization Of Turbulent Mixing Research Articles

A study on the baroclinic structure of the abyssal circulation

In this paper, the linear continuously tratified model of the abyssal circulation proposed by Pedlosky (1992) was extended to include the second order term -(γθzzz) in the vertical turbulent mixing parameterization of\( - \overline {(w\prime \theta \prime )} _z = k_u \theta _{zz} - \gamma \theta _{zzz} \), in whichkv is a vertical diffusion coefficient, and γ is the second order coefficient of turbulent mixing (or simply called γ-term and γ<0 is only allowed). The influence of the γ-term on the baroclinic structure of the abyssal circulation driven by upwelling out of the abyss was investigated. It was found that the γ-term has a noticeable influence on the baroclinic structure of the upwelling driven abyssal circulation. For uniform upwelling, it favors the baroclinic layering of the abyssal circulation in the eastern part of the basin, but prevents the layering in the west. In addition, this parameter was found to decrease the vertically averaging meridional velocity of the abyssal circulation from the west to the east on the southern boundary. For upwelling localized near the eastern boundary, the γ-term favors baroclinic layering of the abyssal circulation in the whole basin. Especially, on the southern boundary the γ-term could strengthen the vertically averaging meridional velocity in the west, but greatly weaken it in the east. The model presented here might be considered as an extension of the Pedlosky baroclinic model of the abyssal circulation.

Nonlocal Turbulent Mixing Based on Convective Adjustment Concepts (Ntac)

A nonlocal turbulent mixing parameterization is introduced in this study and denoted by the acronym NTAC, which stands for Nonlocal parameterization of Turbulent mixing using convective Adjustment Concepts. NTAC uses the average value of quantities in the turbulent domain in much the same way that local convective adjustment schemes use the average potential temperature. Averages are determined in the region with non-convective turbulence using information from the two end layers (denoted by TLA, Two Layer Average), while all layers contribute to the average in regions with convective turbulence (denoted by CLA, Convective Layer Average). The NTAC parameterization estimates the mixing percentage and uses this percentage as a mixing coefficient. These percentages are determined from a simplified turbulent kinetic energy equation. The scheme is versatile, conservative, and when programmed efficiently the proposed parameterization is a computationally acceptable nonlocal procedure that can be used in many existing numerical weather prediction forecast models. Numerical weather forecast model simulations using the NTAC parameterization and traditional K-theory are compared against radiosonde data. The accuracy of the proposed NTAC parameterization is found to be competitive with K theory. The greatest improvement of the NTAC over K-theory occurs during the daytime and early nighttime hours when (dry) convective activity is high. Also, areal cloud coverage is increased by the NTAC parameterization. Our findings show that the greatest nonlocal vertical mixing occurs between the layer nearest the earth's surface and the remaining layers making up the planetary boundary layer.

The Computation of Diapycnal Diffusive and Advective Scalar Fluxes in Multilayer Isopycnic-Coordinate Ocean Models

Abstract This paper addresses the problem of how to numerically incorporate diapycnal mixing and advection processes into isopycnal ocean general circulation models. A general expression of diapycnal velocity is derived for the case in which density is a function of both potential temperature and salinity. The expression is independent of turbulence closure parameterizations and thus can be viewed as a generalized definition of diapycnal velocity. With this definition, it is simple to derive expressions of diapycnal velocity for different parameterizations of turbulent mixing in isopycnal ocean models. Numerical algorithms are developed to overcome difficulties associated with massless layers in computing diapycnal diffusive and advective scalar fluxes in isopycnic-coordinate ocean models. In the diapycnal diffusive flux computation, a mass-weighted averaging is used to prevent linear instability in the time integration. In diapycnal advective flux computation, it is shown that the diapycnal mass exchange...

Fine structure and microstructure characteristics across the northwest Atlantic Subtropical Front

Vertical profiles of temperature, salinity, horizontal velocity, rate of dissipation of turbulent kinetic energy, and thermal variance are used to examine the parameterization of turbulent mixing associated with internal waves in an upper ocean front. Previous attempts to quantify the rate of turbulent dissipation [e.g., Gregg, 1989; Polzin et al., 1995] are based upon dynamical models of wave‐wave interactions using the Garrett and Munk [1979] (GM) spectrum. Non‐GM conditions (vertical and horizontal anisotropy, deviations in vertical wavenumber and frequency spectral shapes, and the presence of a background flow) may affect the character of wave interactions, altering the upwavenumber energy flux, which is equated with the rate of turbulent dissipation. Non‐GM conditions in the data are documented, and revisions to the wave‐wave interaction models are discussed. Additionally, the strength of wave‐wave interactions is directly compared with the strength of wave‐mean flow interactions. These data indicate that the dissipation rate is relatively insensitive to the presence of a background flow and anisotropic wave conditions, in agreement with theoretical expectations based upon wave‐wave interaction models and a model of wave‐mean flow interaction at high background Richardson number. These data support the findings of Polzin et al. [1995], who argue that the dissipation rate is most sensitive to variations in wave frequency.

Examples of the role of surface friction in downslope windstorms

Numerical simulations of four mountain wave events over the Colorado Rockies were carried out with a two-dimensional hydrostatic model including a turbulent mixing parameterization in order to investigate the effect of surface friction. Surface friction was found to play a major role in modulating and even in some cases preventing the wave amplification mechanism from producing severe downslope windstorms.

An Inertial Model of Steady Coastal Upwelling

Abstract A nonlinear inertial model of a steady-state coastal upwelling circulation is presented. The model describes a longshore equatorward current and countercurrent structure which is independent of any parameterization of turbulent mixing. Solutions for flat and sloping bottoms are presented.