对流边界层中的一个双高斯型PDF扩散模式

对流边界层（ＣＢＬ）中的污染扩散是非高斯型的。本文在下列三个假设下建立了双高斯型几率分布函数（ＰＤＦ）模式：１．对流边界层任一确定高度铅直速度Ｗ的几率分布函数ｐｗ由两个高斯分布迭加而成；２．从污染源释放的粒子具有源高的铅直速度几率分布，且其轨迹是线性的；３．粒子在地面的反射为全反射，在混合层高度Ｚｉ为全反射或有部分吸收。然后分析了三个高度上铅直速度Ｗ的一些统计特征量，比较了由ＰＤＦ模式计算的横风向积分浓度和Ｌａｍｂ的数值模拟［１－３］，Ｄｅａｒｄｏｒｆｆ的水槽模拟［４－６］结果，并用美国ＣＯＮＤＯＲＳ计划的外场试验资料［７］对ＰＤＦ模式进行了验证，结果均相当一致。

A DOUBLE GAUSSIANS PDF MODEL ON DISPERSION IN CONVECTIVE BOUNDARY LAYERS

he dispersion in the convective boundary layers (CBL) is non Gaussians. A double Gaussians PDF model is presented on the basis of three assumptions: 1. the probability distribution function of vertical velocity, pw at any given height is the sum of two Gaussian distributions: 2. the tracers are responding to pw. the probability distribution function, at the source height with straight line trajectories: 3. the reflection of tracers at surface and Zi, themixing depth, is simple reflection. or some of the tracers are absorbed at Zi. Some statistical characteristics of vertical velocity w at three heights are analysed. The contrast of crosswind integral concentration between this model and Lamb's numerical modeling, Deardorff's tank experiment shows considerable agreement. The double gaussians model is also supported by the fields observed data of project CONDORS in the U. S. A.