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Tetsuji Yamada

Abstract

Project MOHAVE (Measurement of Haze and Visual Effects) produced a unique set of tracer data over the southwestern United States. During the summer of 1992, a perfluorocarbon tracer gas was released from the Mohave Power Project (MPP), a large coal-fired facility in southern Nevada. Three-dimensional atmospheric models, the Higher-Order Turbulence Model for Atmospheric Circulation–Random Puff Transport and Diffusion (HOTMAC–RAPTAD), were used to simulate the concentrations of tracer gas that were observed during a portion of the summer intensive period of Project MOHAVE. The study area extended from northwestern Arizona to southern Nevada and included Lake Mead, the Colorado River Valley, the Grand Canyon National Park, and MPP. The computational domain was 368 km in the east–west direction by 252 km in the north–south direction. Rawinsonde and radar wind profiler data were used to provide initial and boundary conditions to HOTMAC simulations. HOTMAC with a horizontal grid spacing of 4 km was able to simulate the diurnal variations of drainage and upslope flows along the Grand Canyon and Colorado River Valley. HOTMAC also captured the diurnal variations of turbulence, which played important roles for the transport and diffusion simulations by RAPTAD. The modeled tracer gas concentrations were compared with observations. The model’s performance was evaluated statistically.

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Tetsuji Yamada

Abstract

A simple prognostic equation for predicting the development of the nocturnal surface inversion height is constructed from the thermal energy equation. The purpose of the paper is to provide a simple method to estimate the nocturnal surface inversion heights to augment the prediction of the mixed-layer heights (Yamada and Berman, 1979) for regional-scale pollutant dispersion models. A significant improvement of the present model over previous simple models is the inclusion of atmospheric cooling due to longwave radiation. Another important difference, which considerably simplifies the present model, is the adoption of an empirical expression for the potential temperature profile. Predictions agree quite well with the data of the Wangara experiment.

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Tetsuji Yamada

Abstract

A capability to address positive and negative buoyancy was added to the Higher-Order Turbulence Model for Atmospheric Circulation–Random Puff Transport and Diffusion (HOTMAC–RAPTAD) modeling system. The modeling system was applied to simulate dense gas plumes, and the modeled concentrations were compared with observations reported in the Modelers’ Data Archives (MDA). Sampling sites reported in MDA were located mostly 50–800 m from the source over flat terrain. To detect a peak concentration, RAPTAD sampling sites were placed on the arcs whose radii correspond to the sampling distance reported in MDA. Concentration averaging time for a peak concentration was varied from 1 to 600 s. RAPTAD simulation time varied from 4 to 30 min. The overall performance of the current model in terms of geometric mean biases, geometric variances, and residual plots was found to be at least as good as those of the better models examined previously with the same dataset.

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