城市近地层风速廓线及风速拐点的数值模拟研究

The study of urban near surface layer is an important and frontier field in the boundary layer meteorology research. The understanding of the vertical structure of the urban near surface layer plays an important role in simulating the land-atmosphere interaction in urban area. But so far, the vertical structure of the urban near surface layer is still uncertain. It can only be determined by empirical formulae derived from observations and numerical experiments..In this study, we will use large eddy simulation (LES) to reveal the velocity profile in the urban near surface layer. We will focus on the relationship between the characteristics of the urban canopy layer and the inflection point in the velocity profile and propose a parameterization for the inflection point. Thus we can determine the vertical structure of the urban near surface layer, analyze the applicability of Monin-Obukhov Similarity Theory (MOST) in the urban near surface layer, and revise the existing models..The main research contents of this project include: 1. The influence of building distribution on the wind profile and wind speed inflection point of urban near surface layer under ideal conditions; 2. Real field simulation of wind field in urban area; 3, Revision of existing urban canopy parameterization scheme. This study is characterized by the use of LES to simulate the wind field structure in the urban near surface layer, the use of wind speed inflection point as the basis for judging the urban rough sublayer, so as to quantitatively obtain the thickness of the rough sublayer, and then clear the vertical structure of the urban near surface layer, and discuss its relationship with the underlying morphological features. Based on the simulation results of the real underlying surface, the representative of turbulence observation in the urban near surface layer is also discussed..

城市近地层研究是边界层研究的一个重要和前沿的领域。深入认识和理解城市近地层的垂直结构对城市地区的地-气相互作用的模拟有着极其重要的作用。但到目前为止，城市近地层的垂直分层结构尚无定论，仅由观测和数值实验推导得到的经验公式所确定。.本项目拟使用大涡模拟方法研究城市近地层风场分布，得到平均风速的垂直廓线。重点讨论风速拐点出现的高度，以及其与城市冠层形态学参数的关系，从而确定城市粗糙子层的高度以及城市近地层的垂直结构，探讨Monin-Obukhov相似性理论（MOST）在城市近地层的适用性，并改进现有的城市冠层参数化方案。.本项目的主要研究内容包括：1、理想条件下建筑物分布对城市近地层风速廓线及风速拐点的影响；2、城市近地层风场的真实模拟；3、MOST及现有城市冠层参数化方案的修正。本研究的特色在于通过利用大涡模拟技术模拟城市近地层的风场结构，提出用风速拐点作为城市粗糙子层的判断依据，从而定量地得到粗糙子层的厚度，进而明确城市近地层的垂直结构。同时本项目利用真实下垫面的模拟结果，讨论了城市近地层湍流观测的代表性问题。

城市近地层研究是边界层研究的一个重要和前沿的领域。深入认识和理解城市近地层的垂直结构对城市地区的地-气相互作用的模拟有着极其重要的作用。但到目前为止，城市近地层的垂直分层结构尚无定论，仅由观测和数值实验推导得到的经验公式所确定。.本项目利用大涡模拟以及外场观测的结果分析和探究城市近地层的垂直结构。本项目的主要研究内容包括以下两点：.1、.利用PALM模式模拟了多组理想建筑群算例模型在不同条件下的风场特点以及真实建筑群（南京市委党校）的风场特征。通过与观测结果的对比研究发现，在垂直方向上，真实建筑群风场的平均垂直廓线不能用单一幂指数廓线表示，其垂直廓线按照建筑物高度变化呈现多级分层分布。.2、.利用不同高度的湍流观测资料，分析复杂下垫面近地层湍流通量的垂直结构。分析结果表明：在冠层之上的粗糙子层当中，城市下垫面的近地面动量通量、感热通量和潜热通量都随高度增加，这些结果意味着在复杂下垫面之上实施通量观测需要在较高的离地高度上进行其观测结果才具有较为充分的局地代表性，在城市地区较低高度上的湍流通量观测结果会出现偏低估计。