Application of a coupled prognostic model to turbulence and dispersion in light-wind stable conditions, with an analytical correction to vertically resolve concentrations near the surface
- 作者：Ashok K. Luhar ; ashok.luhar@csiro.au ; Peter J. Hurley
- 关键词：Calm winds ; Cardington data ; Horizontal meandering ; Idaho Falls experiment ; Mesoscale modelling ; Model resolution ; Stable boundary layer ; TAPM
- 刊名：Atmospheric Environment
- 出版年：2012
- 期刊代码：11_13522310
- 类别：env
- 出版时间：May, 2012
- 卷：51
- 期：Complete
- 页码：56-66
- 文件大小：1381 K
摘要
We apply a three-dimensional prognostic model, namely TAPM, consisting of coupled meteorological and air pollution modules to simulate the turbulence and short-range dispersion (about 0.5聽km) of a near-surface tracer release measured during the 1974 Idaho Falls experiment in light-wind stable conditions. We find that the model substantially underestimates the concentration data. An examination of the near-surface turbulence levels reveals that the modelled vertical turbulence is similar in magnitude to the data but the horizontal component is seriously underestimated. We investigate the latter through a comparison of the boundary condition for the turbulent kinetic energy (TKE) in the model with turbulence data from the U.K. Met Office鈥檚 Cardington site, and propose a semi-empirical modification to the TKE boundary condition that accounts for the observed horizontal meandering of the air not represented in the model. This modification increases the modelled horizontal turbulence for the Idaho Falls case, in accordance with the observations, but leads to a further underestimation of the observed concentrations. We attribute this underestimation to the inadequacy of vertical resolution in the model in resolving the concentration gradients near the ground. It is not feasible to simply increase the vertical model resolution near the surface, and instead we derive an analytical scheme based on a mass-balance approach that corrects the modelled concentrations at the lowest model level for such gradients. A聽remarkable improvement in the predicted concentrations is obtained following the application of the derived correction factor. This factor can be easily incorporated in a typical model for point sources and is valid for all stabilities. Lastly, it is clear that more research is required on horizontal flow meandering and its incorporation in prognostic models.