Study on Characteristic of Standard Deviation of Wind Direction Fluctuation for Atmospheric Dispersion Simulation

Predictions of atmospheric dispersion based on wind-tunnel experiments and numerical simulations are generally executed under the quasi-steady state of wind fields. They however fail to consider the fluctuations in realistic wind directions. Therefore, the dispersion of air pollutants is often underestimated leading to an overestimation of their maximum concentration. For accurate estimations of atmospheric dispersion, it is important to know the variations in wind fields. In this study, the characteristics of the hourly standard deviation of wind direction fluctuation (σ θ ) were investigated using elevated observational data along the coast of the Japan Sea. The conditions of meteorological fields and of terrains were similar to those around thermal or nuclea r power plants. The results suggested that σ θ was mainly dependent on wind speed and the atmospheric stability. However , σ θ varied widely even for the same meteorological conditions, indicating the influences of the surrounding terrain and long-period wind fluctuations.