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（CEAFM），2部门。约翰霍普金斯大学机械工程系，巴尔的摩MD 21218，瑞士联邦洛桑理工学院，摘要：学术价值：在水文学中，获得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。该理论假设一个均匀的陆地表面，但也经常被发现是可以接受的，由于在ABL的湍流，这有效地混合了各种来源和景观的不均匀性的流动在异质性的自然陆地表面。因此，了解和预测土地异质性和大气层结如何影响与这一混合过程相关的长度尺度是至关重要的。具体而言，混合层的高度，和有效的“平均”）粗糙度长度的温度和湿度的表面通量是需要制定简化的模型。在拟议的研究中，大涡模拟（LES）的conventientflow和运输的ABL将进行识别的混合性能的湍流混合在各种条件下的分层和空间不均匀的粗糙度属性，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的动力学模型，已被证明是特别适合捕捉未解决的小尺度湍流物理在复杂的环境中，其中concentration偏离各向同性，惯性范围行为的经典假设。动态过程消除了指定可调模型系数的需要。扩展的动态模型，以考虑标量传输将实施。通过一系列参数化的高分辨率模拟（参数LES），其中表面粗糙度，几何结构，表面温度和/或热通量系统地变化，这些功能驱动的动态ofland-atmosphere交换超过异质地形将被量化，并建立其相关的长度尺度。这一信息将用于获取区域尺度通量的新战略，如现实地形上的热通量和蒸发。LES和参数化的现场验证将使用计划的瑞士MosaicExperiment期间收集的数据进行。更广泛的影响：用于模拟天气和地球气候以及预测未来几十年温度变化的大规模（区域或全球规模）地球系统模拟严重依赖参数化来表示大气边界层和陆地表面。LES与准确测试的子网格模型，使我们能够进行评估和发展的新的，仔细和单独测试，更大规模的模型的组成部分。提高大规模模型各个组成部分的可信度是决策机构以及最终更广泛的公众更认真对待预测的必要步骤。通过我们独特的研究生培训计划，也实现了拟议的研究活动的更广泛的影响。学生们通过各个部门的课程工作在科学方面受到严格的训练，可能会导致M.S.通过CEAFM的双学位课程，他获得了机械工程学位和地理与环境工程系的博士学位。而且，通过地理和环境工程课程，他们将在社会与环境之间的界面上拥有更广泛的知识。该方案是独特的，其重点是人类行为与自然之间的相互作用随着时间的推移，并在其结构，它结合了政治和人文方面与环境科学的范围。霍普金斯大学的计划已经获得了相当大的认可，其成功影响公共政策，通过坚实的科学。

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.