A 3-dimensional nonhydrostatic dispersion modeling system for modeling of atmospheric transport and diffusion over coastal complex terrain in the Hongkong-Shenzhen area

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.

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The Numerical Simulation of Airflow and Dispersion in Three-Dimensional Atmospheric Recirculation Zones

Journal of Applied Meteorology ◽

10.1175/1520-0450-30.7.1005 ◽

1991 ◽

Vol 30 (7) ◽

pp. 1005-1024 ◽

Cited By ~ 23

Author(s):

Paul Dawson ◽

David E. Stock ◽

Brian Lamb

Keyword(s):

Surface Layer ◽

Atmospheric Transport ◽

Three Dimensional ◽

Field Measurements ◽

Ground Level ◽

Turbulence Closure ◽

Numerical Code ◽

Recirculation Zones ◽

Transport And Diffusion ◽

And Diffusion

Abstract A three-dimensional, nonhydrostatic numerical code using the two-equation turbulence closure was developed to model the atmospheric transport and diffusion of pollutants over buildings and a three-dimensional hill. The standard engineering two-equation, first-order turbulence closure was modified to account for surface layer effects and the reduced production of dissipation in the region above the surface layer found in an atmospheric boundary layer. The computations for the dispersion of a building rooftop release showed good agreement with wind tunnel measurements, except when very close to the ground. The transport and dispersion of a plume over a 300-m conical hill, Steptoe Butte, was also simulated. The computations are compared with near ground-level field measurements.

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