• 关键词：

• 基金项目：

• 张锡福
• 中国科学院大气物理研究所

• 邹孝恒
• 中国科学院大气物理研究所

• 贾新媛
• 中国科学院大气物理研究所

• 杨锦德
• 中国科学院大气物理研究所

• 摘要：在北京北郊气象铁塔(325m高)的160 m高度上释放平衡气球,用双经纬仪定位的方法得到拉格朗日表示法的风速脉动资料.分析了气球运行轨迹特征以及地形风与热岛环流叠合的复合环流.用相继释放的两个气球的轨迹计算了水平扩散参数σ_y.发现扩散曲线在一公里左右发生转折,这反映了城市和郊区两种边界层特征.以一公里为界,将所得湍流资料分成前后两段,每段资料用滑动平均方法计算σ_y.计算出来的属于城市和郊区边界层的两条σ_y随距离而变的曲线有明显的不同.若将两段资料合并则可计算一公里以远的σ_y.无论两段资料的个数相同或不相同,得到的σ_y随距离变化均具有一公里以远的边界层特征.这说明城郊区的非均匀性对湍流高频段影响显著.而低频部分则受大尺度非均匀性的影响.似乎是其发展趋势决定了扩散的特性.此外还发现Pasquill的大气稳定度分类方法中.用160m高度的风速比用地面风速得到的高空扩散规律更符合实际.

• Abstract：Velocity fluctuations in the Lagrangian frame have been observed by using a double-theodolite system to track balanced balloons released at the height of 160m of the 325m tower which is located on the north suburb of Beijing. The trajectories and the complex circulation phenomena produced by geographical and thermal island effects are analysed. Curves of lateral diffusion parameters σ_y, as a function of down wind distance, are estimated from the balanced balloon pairs which are not released, at the same time, but bent (or jump) at the distance about 1 km from the tower, the difference of the two σ_y curves shows the features of atmospheric diffusion within and beyond the distance of 1 km respectively. So velocity fluctuation data are divided into two series at a distance of 1 km. The two curves of σ_y estimated from running mean of these two series also reveals the difference between urban and suburb boundary layers. But no matter if the number of the lateral velocity fluctuations for the two series is equal or not, the σ_y curves estimated by running mean of the combination of these two series indicates the characteristics of the boundary layer beyond the distance of 1 km.In the analysis of σ_y in various atmospheric stability defined by Pas-quill's categories, it is found that it would be reasonable by using wind velocity at a height of 160m to classify the Pasquill's stability categories instead of the surface wind velocity.

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