One-dimensional Turbulence Model Research Articles

Numerical study of dispersion in the convective boundary layer

A simple one-dimensional turbulence model developed by Sun and Chang (1986a, J. clim. appl. Met. 25,1445–1453) is modified by including γ c (a reference potential temperature gradient) in the diffusion term of the heat equation to study the moist convective boundary layer. The results show that the stratification becomes neutral to slightly unstable in the middle and lower mixed layer but slightly stable in the upper mixed layer as observed, while the wind, moisture and eddy fluxes are very similar to those discussed by Sun and Chang. The results from the one-dimensional model are then applied to a two-dimensional dispersion model. The new concentrations are better than the previous results (Sun, 1986, Atmospheric Environment 20, 1877–1886). The ground level concentration, the mean height of concentration, and vertical speed simulated from this higher order closure model are also in good agreement with field experiments, water tank simulations and results obtained from the statistical models.

A one-dimensional turbulence model; Enstrophy cascades and small-scale intermittency in decaying turbulence

Abstract Severe unidirectional Fourier truncation of the equations for 2-D incompressible flow leads to a system of three coupled PDEs in one space dimension with the same quadratic invariants as the original set (i.e. energy and enstrophy). Numerically generated equilibria for inviscid, truncated versions of the reduced system are well approximated by Kraichnan's energy-enstrophy equipartition spectra. Viscous calculations for decaying turbulence at moderate resolution (1024 degrees of freedom) also appear to be consistent with a direct, k −3, enstrophy cascading inertial range when the dissipation is small. Dissipation range intermittency in the form of spatially intermittent enstrophy dissipation with occasional strong bursts producing linear phase locking is also observed. In contrast to full 2-D simulations, no tendency towards the emergence of isolated, coherent vorticity structures is observed. The model consequently mimics some, but not all, of the properties of the full 2-D set.

A one-dimensional mixed-layer model for stratified shelf seas with tide- and wind-induced mixing

In order to study the onset, development and breakdown of the seasonal thermal stratification in shelf seas a one-dimensional turbulent erosion model is formulated. The model contains a turbulent surface mixed layer caused by wind mixing, a turbulent bottom layer caused by tidal turbulence and a non-turbulent thermocline in between. The generation of turbulent energy within the mixed layer is explained partly by shear production in a quasi-stationary Ekman layer and partly by free convection due to a downward mass flux at the sea surface. The parameters to obtain the energy budget and the heat budget are taken from measurements and from literature. The model equations do not contain any freely adjustable parameter.

Operational Evaluation of a Turbulence Closure Model Forecast System

Abstract A one-dimensional turbulence model has been coupled with the large-scale fields of a hemispheric model so as to produce a high-resolution marine boundary layer forecast system. Model initialization is performed either by use of individual ship soundings or from standard fields of the hemispheric model. Detailed boundary layer forecasts in specified oceanic regions are desirable for many purposes, but large-scale model forecasts with such high resolution are computationally impractical. This paper presents results from approximately 90 different 24 h forecasts at the location of four different ocean station vessels. We statistically compare model forecast profiles of temperature and moisture with verifying soundings, and also evaluate persistence as a forecast. Results consistently show a significant improvement of the model forecasts relative to persistence. The one-way influence driving force provided by large-scale time derivative terms derived from the hemispheric model is found to be very imp...

The Relationship between Downward Irradiance and Upper Ocean Structure

The relationship between downward irradiance and upper ocean structure has been studied using a numerical model. Two general classes of irradiance parameterizations were utilized. The first (case I) employed a single attenuation length while the second (cast II) involved two attenuation lengths. The latter formulation provided for enhanced absorbance in the upper few meters. Wind speeds of 0, 1, 2, 3, 4, 5, 10 and 20 m.s−1 were used for the simulations in order to characterize heat versus wind dominated regimes. A one-dimensional second moment turbulent closure model was selected for the study so that heat could be treated differentially with depth. The case II results indicated warmer surface temperatures, shallower mixed layers, and more intense thermoclines than case I for wind speeds <10 m s−1. Results converged for higher wind speeds. There was considerably greater sensitivity to wind speed for case II when compared with case I. Mean horizontal velocity as well as thermal structure was sensitive to the empirical formulation of downward irradiance. For low wind speeds the turbulent energy budget is dominated by shear production, dissipation and the diffusion of turbulent kinetic energy, regardless of parameterization. For high wind speeds, shear production is balanced by dissipation. The results of this study provide strong indications that downward irradiance and its proper parameterization are important in determining upper ocean structure and may have implications for large-scale climate studies.