Scale Effects and Heterogeneity in Land-atmosphere Interactions: Large Eddy Simulation Studies, Parameterizations and Field Validations

1环境与应用流体力学中心，2系。机械工程系，约翰霍普金斯大学，巴尔的摩，马里兰州21218，3Ecole理工学院，瑞士洛桑，以及摘要：在水文学中，获取区域尺度蒸发的主要实用方法仍然是基于大气边界层(ABL)的经典相似理论。该理论假设地表是均匀的，但由于ABL中的湍流有效地混合了各种来源和地形上的不均匀，所以在非均匀自然地表上的流动也经常被发现是可以接受的。因此，了解和预测土地非均质性和大气分层如何影响与这一混合过程相关的长度尺度是至关重要的。具体地说，混合层高度和地表温度和湿度通量的有效“平均”粗糙度长度是建立简化模型所必需的。在拟议的研究中，将通过大涡模拟(LES)来研究ABL内湍流流动和输送的混合特性，以确定不同层结条件下的湍流混合特性和空间非均匀粗糙度特性，包括分形分布。数值模拟将采用新开发和测试的拉格朗日尺度相关动力学模型，该模型已被证明特别适合于在湍流偏离各向同性、惯性范围行为的经典假设的复杂环境中捕捉未分辨的小尺度湍流物理。动态过程消除了指定可调模型系数的需要。将实施动态模型的扩展，以考虑标量传输。通过系统地改变地表粗糙度、几何排列、地表温度和/或热通量的一系列高分辨率参数模拟(参数大涡模拟)，驱动非均匀地形上陆地-大气交换动力学的特征将被量化，并建立相应的长度尺度。这些信息将被用于获取区域尺度通量的新战略，例如实际地形上的热通量和蒸发。将使用在计划中的瑞士Mosaic实验期间收集的数据对LES和参数进行现场验证。更广泛的影响：用于模拟天气和地球气候并预测未来几十年气温变化的大规模(区域或全球规模)地球系统模拟，在很大程度上依赖于参数化来表示大气边界层和陆地表面。具有精确测试的次网格模型的LES使我们能够对更大比例模型的新的、仔细的和单独测试的组件进行评估和开发。提高大型模型单个组件的可信度是决策机构更认真对待预测的必要步骤，最终也是更广泛的公众的预测。拟议研究活动的更广泛影响也通过我们独特的研究生培训计划实现。这些学生通过在不同系的课程工作接受严格的科学培训，可能会获得机械工程硕士学位，并通过CEAFM的双学位计划获得地理和环境工程系的博士学位。而且，通过地理学和环境工程专业的课程，他们将在社会与环境的界面上有更广泛的知识。这一计划的独特之处在于，它的重点是人类行为与自然之间随时间的相互作用，其结构将政治和人文方面与环境科学相结合。霍普金斯计划因其成功地通过坚实的科学影响公共政策而获得了相当大的认可。

1Center for Environmental and Applied Fluid Mechanics (CEAFM), 2Dept. of Mechanical Engineering, The Johns Hopkins University, Baltimore MD 21218, 3Ecole Polytechnique Federale Lausanne, Switzerland, and Dept. of Geography and Environmental Engineering, The Johns Hopkins University, Baltimore MD 21218.Summary:Intellectual merit: In hydrology, the main practical approach to obtain regional scale evaporation continues to be based on classical similarity theory of the atmospheric boundary layer (ABL). The theory assumes a uniform land surface yet has also often been found acceptable in flows over heterogeneous natural land surfaces due to the turbulent flow in the ABL, which efficiently blendsthe various sources and inhomogeneities across the landscape. It is thus essential to understand and predict how land heterogeneity and atmospheric stratification affect the relevant length-scales associated with this blending process. Specifically, the height of blending layers, and effective 'average') roughness lengths for surface fluxes of temperature and humidity are of needed to formulate simplified models. In the proposed research, Large Eddy Simulations (LES) of turbulentflow and transport in the ABL will be conducted to identify the blending properties of turbulent mixing under various conditions of stratification and spatially heterogeneous roughness properties, including fractal distributions. Numerical simulations will employ the newly developed and testedLagrangian scale-dependent dynamic model, which has been shown to be particularly well suited to capture unresolved small-scale turbulence physics in complex environments in which turbulencedeviates from the classical assumptions of isotropic, inertial-range behavior. The dynamic procedure eliminates the need to specify tunable model coefficients. Extensions of the dynamic model to account for scalar transport will be implemented. Through a parametric series of high-resolution simulations (parametric LES) where surface roughness, geometric arrangements, and surface temperature and/or heat flux are varied systematically, those features which drive the dynamics ofland-atmosphere exchange over heterogeneous terrain will be quantified, and their relevant lengthscales established. This information will be used in new strategies for obtaining regional scale fluxes such as heat flux and evaporation over realistic terrain. Field validations of the LES and parameterizations will be conducted using data collected during the planned Swiss MosaicExperiment. Broader impacts: Large-scale (regional or global-scale) earth-system simulations, used to simulate weather and the Earth's climate and project temperature changes in the coming decades, rely heavilyon parameterizations to represent the atmospheric boundary layer and the land surface. LES with accurately tested subgrid models allows us to undertake assessments and developments of new,carefully and individually tested, components of the larger scale models. Increasing the trustworthiness of individual components of large-scale models is a necessary step for predictions to be taken more seriously by policy-making bodies, and ultimately also by the broader public. Broader impact of the proposed research activity is also achieved through our unique graduate studenttrainingprogram. The students are trained rigorously in science through course-work in various departments, possibly leading to a M.S. degree in Mechanical Engineering and a PhD in theDepartment of Geography and Environmental Engineering through the CEAFM's Dual DegreeProgram. And, through the program in Geography and Environmental Engineering they will have abroader knowledge at the interface between society and environment. This program is distinctive inthe scope of its focus on the interaction between human behavior and nature over time and in itsstructure, which combines political and human aspects with the science of the environment. TheHopkins program has garnered considerable recognition for its success in influencing public policythrough solid science.