内陆丘陵河谷地区小风条件下的大气扩散模拟研究

Atmospheric dispersion simulation in low wind conditions in inland hills and valleys

针对湖南中部丘陵河谷地区的气象特点,开展了小风条件下大气扩散的数值模拟研究,并与示踪实验结果进行比较.模拟采用美国EPA推荐的非稳态拉格朗日高斯烟团模式CALPUFF,以加密的地面气象观测资料、边界层垂直廓线观测资料和铁塔多层湍流观测资料作为模拟气象场的输入.中等风速和小风条件下的模拟结果表明:模式对地表类型及资料的分辨率敏感;模式默认的地表参数不能准确地反映当地的实际情况;默认的微气象学法模拟方案给出的近场扩散浓度明显偏低,采用实测湍流资料可明显改善模拟结果.根据实际下垫面情况和塔层湍流实测资料,对模式的土地利用类型和对应的地表参数、近地层湍流速度参数化方案进行了修正,修正后方案的模拟结果与实测值吻合较好,与使用实测湍流廓线观测资料的模拟效果接近,表明模式参数的本地化和优化是必要的.

The atmospheric dispersion under conditions with moderate and low winds was simulated for the hill and valley area in the centre of Hunan province. The non-steady-state Lagrangian Gaussian puff model CALPUFF recommended by USEPA was used in the simulation. The inputs of the meteorological model included the intensive observations of surface wind and temperature,profiles of wind and temperature in the boundary-layer,and the multi-layer turbulence data from the tower. Results showed that the model was sensitive to the categories and resolution of land use data. Simulated results were compared with those of the tracer experiments. It is seen that the near field concentration simulated by the default micrometeorological scheme was significantly lower than that observed in the tracer experiment. This is partly because the default land use category and the corresponding surface parameters in the model cannot represent the actual surface conditions in the simulated area. When utilizing the direct measurements of turbulence,the modeled results were greatly improved. Modification was made for land use data,geophysical parameters and the parameterization scheme of the turbulent velocities of the model,based on the actual underlying surface features and the measured turbulence data. The simulated results of the modified scheme were in good agreement with the measured values,and were comparable with those modeled with the direct measurements of turbulence profiles. These facts show the effectiveness and the necessity of the modification.