CAREER: Multi-Scalar Transport and Similarity in the Urban Boundary Layer

全球一半以上的人口居住在城市地区，城市通过两大途径对大气产生重大影响：城市形态（即地表性质的变化）和城市功能（即释放热量和质量的人为活动）。这两条路径通过大气边界层中动量、能量和质量的湍流交换而发生，并带有城市形式和功能的“独特指纹”。对于越来越精细的气候和数值天气预报（NWP）模式来说，如何反映世界各地不同城市的这些“独特指纹”是一个持续的挑战，但同时又要以一种可推广和计算易于处理的方式。由于对多尺度输运的认识不完全，不同尺度的人为起源在城市表层是否服从相似关系尚不清楚。这也是推广多尺度城市陆气交换的关键障碍之一。特别是，将城市功能对地表-大气交换的影响纳入气候和NWP模式几乎完全缺失。因此，总体目标是提高对多标量输运的基本理解，并为地表-大气交换提供物理上现实的、可推广的估计，特别是对较少探索的标量。该项目将得出下一代城市气候建模工具所需的研究结果，这些工具可用于制定更精确的（即针对城市或社区的）缓解和适应气候变化的措施。为了实现整个项目的目标，这个项目的方法是由城市冠层与植被中的流动和运输的关键比较所驱动的，这已经得到了广泛的研究。这种方法将对两者之间的理论和模型的可转移性产生新的见解，为在现有植被对应模型的基础上开发城市特定的地表-大气交换模型提供信息。为了加深对多标量迁移和相似性偏离的基本理解，我们将分别在城市形态和功能异质性的微观和局部尺度上研究造成标量不相似性的机制。通过首先推导“城市轮廓生成”模块来概括城市形态和功能，将系统地研究微观和局部尺度上的多标量运输的理解（目标1）。然后，将测试关于多标量输运及其相似性的假设，以推进基本理解（目标2）。新的认识将有助于改善城市地表-大气交换模型和依赖于标量相似理论的观测结果的解释（目标3）。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

More than half of the global population live in urban areas, which nontrivially modify the atmosphere through two broad pathways: urban form (i.e., changes in surface properties) and urban function (i.e., anthropogenic activities emitting heat and mass). These two pathways occur via turbulent exchanges of momentum, energy and mass in the atmospheric boundary layer and carry ‘distinct fingerprints’ of a city’s form and function. For increasingly fine-scale climate and numerical weather prediction (NWP) models, it is a persistent challenge to reflect these ‘distinct fingerprints’ of different cities across the world, yet in a manner that is generalizable and computationally tractable. Due to incomplete understanding of multi-scalar transport, whether different scalars of anthropogenic origins obey similarity relations in the urban surface layer remains unclear. This is also one of the key stumbling blocks to generalize urban land-atmosphere exchanges for multiple scalars. In particular, incorporating the effect of urban function on surface-atmosphere exchanges into climate and NWP models is almost completely missing. Therefore, the overarching goal is to improve basic understanding of multi-scalar transport and inform physically realistic, generalizable estimates of the surface-atmosphere exchanges, especially for less explored scalars. The project will lead to findings necessary for the next-generation urban climate modeling tools, which can be implemented to develop more precise (i.e., city or neighborhood-specific) mitigation and adaptation measures with changing climates. To achieve the overall project goal, the approach of this project is motivated by a critical comparison between flow and transport in the urban canopy versus vegetated one, which has been extensively studied. Such an approach will generate new insight into the transferability of theories and models between the two, informing development of urban-specific models for surface-atmosphere exchanges based on the existing ones for vegetation counterpart. To advance basic understanding of multi-scalar transport and departure from similarity, the mechanisms responsible for scalar dissimilarity will be separately investigated at the micro- and local scale of heterogeneities in urban form and function. Understanding of multi-scalar transport at both the micro- and local scales will be systematically studied by first deriving a ‘city profile generation’ module to generalize urban form and function (Aim 1). Then, hypotheses regarding multi-scalar transport and their similarity will be tested to advance basic understanding (Aim 2). The new understanding will help improve urban surface-atmosphere exchange modeling and interpretation of observations that rely on scalar similarity theory (Aim 3).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.