Notes on the Turbulence Closure Model for Atmospheric Boundary Layers

The response of the fluid stably stratified over the infinite slope was investigated by linear theory when finite length 2l in it was heated or cooled. If the angle of the slope was small, the nature of the flow near the slope changed depending on whether the half height of the slope h*S=lsin * (* is angle of slope) was higher than that of thermal boundary layer h*T=a(*/N)1/3l1/3 (**3.5), which was developed over the heat island whose length was 2l, or not.On the real slope h*s>h*T was often satisfied at night and the flow was close to the results from Prandtl theory, but h*s

Section: Numerical Experimentsmentioning

confidence: 89%

The Difference of the Slope Wind Between Day and Night

Kumakura¹

1984

“…N01, after determining the other closure constants, chose the value of C 3 in order that the slope of the dimensionless gradient function f h for heat approaches 4.7 as z ! y (Businger et al 1971), where C 2 was selected to be 0.65 following Gambo (1978). If C 2 is selected to be 0.75, however, C 3 becomes 0.352 and falls within the range of the previous studies.…”

Section: Closure Constants In the Mynn Modelmentioning

confidence: 94%

“…Although most of the previous e¤orts to improve the MY model focused on excluding singular solutions (e.g., Mellor and Yamada 1982;Galperin et al 1988;Helfand and Labraga 1988;Gerrity et al 1994;Janjić 2002), several authors did attempt to improve the problems described above (e.g., Gambo 1978;Sun and Ogura 1980;Kantha and Clayson 1994;Cheng et al 2002). Using a database of a large-eddy simulation (LES) for dry ABLs under di¤erent stratifications, Nakanishi (2001, hereafter N01) recently proposed an improved MY model in which a newly-proposed diagnostic equation for the turbulent length scale and reevaluated model constants are incorporated.…”

Section: Introductionmentioning

confidence: 99%

Development of an Improved Turbulence Closure Model for the Atmospheric Boundary Layer

Nakanishi

Niino

2009

788

447

An improved Mellor-Yamada (MY) turbulence closure model (MYNN model: Mellor-YamadaNakanishi-Niino model) that we have developed is summarized and its performance is demonstrated against a large-eddy simulation (LES) of a convective boundary layer. Unlike the original MY model, the MYNN model considers e¤ects of buoyancy on pressure covariances and e¤ects of stability on the turbulent length scale, with model constants determined from a LES database. One-dimensional simulations of Day 33 of the Wangara field experiment, which was conducted in a flat area of southeastern Australia in 1967, are made by the MY and MYNN models and the results are compared with horizontal-average statistics obtained from a threedimensional LES. The MYNN model improves several weak points of the MY model such as an insu‰cient growth of the convective boundary layer, and underestimates of the turbulent kinetic energy and the turbulent length scale; it reproduces fairly well the results of the LES including the vertical distributions of the mean and turbulent quantities. The improved performance of the MYNN model relies mainly on the new formulation of the turbulent length scale that realistically increases with decreasing stability, and partly on the parameterization of the pressure covariances and the expression for stability functions for third-order turbulent fluxes.

“…The turbulent diffusion coefficients (K m , K h , and K q ) in Eqs. (1) to (4) are obtained from Gambo's (1978) formula. F u and F v denote Coriolis parameters.…”

Section: Brief Description Of CMmentioning

confidence: 99%

Numerical Study on the Effect of Buildings on Temperature Variation in Urban and Suburban Areas in Tokyo

Tokairin

Kumakura

Yoshikado

et al. 2006

A numerical investigation of the temperature variation in urban and suburban areas due to the presence of buildings was carried out using a one-dimensional canopy model combined with a meso-scale meteorological model. Since temperature increases in an urban area are caused by sensible heat from building surfaces besides anthropogenic heat and reduction of wind speed due to buildings' drag, we estimated each cause separately to determine the contribution by each to the temperature variation. The simulation was performed for Kanda, an urban area, and for Nerima, a suburban area of Tokyo. Comparisons were made with actual temperatures before the estimation. The comparison indicated that the measured temperatures in the Kanda and Nerima areas were nearly reproduced by the model. The sensitivity analysis indicated that, in a comparison with the temperature in no building environment, the contribution of (i) sensible heat flux from building surfaces to temperature rise was 49% in Kanda and 20% in Nerima, (ii) wind reduction due to drag was 41% in Kanda and 59% in Nerima, and (iii) the effect of the interaction between (I) and (II) was þ10% in Kanda and þ20% in Nerima.