Transport and diffusion in complex terrain (review)

1984 ◽  
Vol 30 (1-4) ◽  
pp. 3-28 ◽  
Author(s):  
Bruce A. Egan
Keyword(s):  
Complex Terrain ◽  
Transport And Diffusion ◽  
And Diffusion

High-Resolution Large-Eddy Simulations of Scalar Transport in Atmospheric Boundary Layer Flow over Complex Terrain

2008 ◽  
Vol 47 (12) ◽  
pp. 3150-3169 ◽  
Author(s):  
Takenobu Michioka ◽  
Fotini Katopodes Chow
Keyword(s):  
High Resolution ◽  
Complex Terrain ◽  
Grid Resolution ◽  
Scalar Transport ◽  
Lateral Boundary ◽  
Scalar Dispersion ◽  
Large Eddy ◽  
Transport And Diffusion ◽  
Horizontal Grid ◽  
And Diffusion

Abstract This paper presents high-resolution numerical simulations of the atmospheric flow and concentration fields accompanying scalar transport and diffusion from a point source in complex terrain. Scalar dispersion is affected not only by mean flow, but also by turbulent fluxes that affect scalar mixing, meaning that predictions of scalar transport require greater attention to the choice of numerical simulation parameters than is typically needed for mean wind field predictions. Large-eddy simulation is used in a mesoscale setting, providing modeling advantages through the use of robust turbulence models combined with the influence of synoptic flow forcing and heterogeneous land surface forcing. An Eulerian model for scalar transport and diffusion is implemented in the Advanced Regional Prediction System mesoscale code to compare scalar concentrations with data collected during field experiments conducted at Mount Tsukuba, Japan, in 1989. The simulations use horizontal grid resolution as fine as 25 m with up to eight grid nesting levels to incorporate time-dependent meteorological forcing. The results show that simulated ground concentration values contain significant errors relative to measured values because the mesoscale wind typically contains a wind direction bias of a few dozen degrees. Comparisons of simulation results with observations of arc maximum concentrations, however, lie within acceptable error bounds. In addition, this paper investigates the effects on scalar dispersion of computational mixing and lateral boundary conditions, which have received little attention in the literature—in particular, for high-resolution applications. The choice of lateral boundary condition update interval is found not to affect time-averaged quantities but to affect the scalar transport strongly. More frequent updates improve the simulated ground concentration values. In addition, results show that the computational mixing coefficient must be set to as small a value as possible to improve scalar dispersion predictions. The predicted concentration fields are compared as the horizontal grid resolution is increased from 190 m to as fine as 25 m. The difference observed in the results at these levels of grid refinement is found to be small relative to the effects of computational mixing and lateral boundary updates.

Application of a model system for the study of transport and diffusion in complex terrain to the TRACT experiment

2002 ◽  
Vol 36 (7) ◽  
pp. 1147-1161 ◽  
Author(s):  
J.C Carvalho ◽  
D Anfossi ◽  
S Trini Castelli ◽  
G.A Degrazia
Keyword(s):  
Complex Terrain ◽  
Model System ◽  
Transport And Diffusion ◽  
And Diffusion

scholarly journals Nocturnal Low-Level Jet in a Mountain Basin Complex. Part II: Transport and Diffusion of Tracer under Stable Conditions

2006 ◽  
Vol 45 (5) ◽  
pp. 740-753 ◽  
Author(s):  
Lisa S. Darby ◽  
K. Jerry Allwine ◽  
Robert M. Banta
Keyword(s):  
Surface Pressure ◽  
Salt Lake ◽  
Low Level ◽  
Stable Conditions ◽  
Basin Scale ◽  
Flow Features ◽  
Transport And Diffusion ◽  
Low Level Jet ◽  
The City ◽  
And Diffusion

Abstract Differences in nighttime transport and diffusion of sulfur hexafluoride (SF6) tracer in an urban complex-terrain setting (Salt Lake City, Utah) are investigated using surface and Doppler lidar wind data and large-scale surface pressure differences. Interacting scales of motion, as studied through the URBAN 2000 field program combined with the Vertical Transport and Mixing (VTMX) experiment, explained the differences in the tracer behavior during three separate intensive operating periods. With an emphasis on nighttime stable boundary layer conditions, these field programs were designed to study flow features responsible for the nighttime transport of airborne substances. This transport has implications for air quality, homeland security, and emergency response if the airborne substances are hazardous. The important flow features investigated included thermally forced canyon and slope flows and a low-level jet (LLJ) that dominated the basin-scale winds when the surface pressure gradient was weak. The presence of thermally forced flows contributed to the complexity and hindered the predictability of the tracer motion within and beyond the city. When organized thermally forced flows were present, the tracer tended to stay closer to the city for longer periods of time, even though a strong basin-scale LLJ did develop. When thermally forced flows were short lived or absent, the basin-scale low-level jet dominated the wind field and enhanced the transport of tracer material out of the city.

Sign in / Sign up

Export Citation Format

Share Document