Analytical and Numerical Studies of Katabatic and Anabatic Flows in Stratified Atmospheric Environments

分层大气环境中下降流和非绝热流的分析和数值研究

• 批准号: 0622745
• 负责人: Alan Shapiro
• 金额: $ 29.29万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-02-01 至 2011-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0622745&HistoricalAwards=false
• 关键词: Analytical; Numerical; Studies; Katabatic; Anabatic

Katabatic and anabatic flows (winds) can be described, most basically, as turbulent natural convection flows along cooled/heated sloping surfaces in a stratified environment. They are ubiquitous in regions of complex terrain at all latitudes. In regions where basins are largely sheltered from synoptic effects, these flows are the building blocks of local weather. Even with a stronger synoptic forcing, pronounced slope flow signals are often apparent. Persistent katabatic winds are typical for vast areas of the earth like Greenland and Antarctica, and play an important role in the regional climate. In heavily industrialized/populated regions extending across basins (like Los Angeles and Phoenix), these local winds exert major controls over energy usage, visibility, fog formation, and pollutant dispersion. Even in their most idealized or elemental forms, slope flows conflate two notoriously difficult aspects of atmospheric dynamics: turbulence and natural convection. Although much progress has been made in the conceptual understanding and numerical modeling of such flows, long-standing difficulties with turbulence modeling in stably-stratified flows, and the variety of flow interactions that can occur with complex topography and surface inhomogeneity (e.g. from irregular snow/ice/soil cover, cloudiness, topographic shading, and land use) make slope flow dynamics a rich area of study. This research will focus on three aspects of katabatic/anabatic flows in stratified environments. First, the Principal Investigator will conduct a theoretical analysis of slope flows induced by inhomogeneous surface buoyancy forcing, in which the classical Prandtl slope flow model will be extended via a spatial similarity constraint to include effects of inhomogeneous slope buoyancy, cross-slope flow, external pressure gradient, ambient wind, and Coriolis force. Second, three-dimensional numerical modeling will be used to test the robustness of the similarity model, specifically with regard to boundary layer thickness, flow intensity, entrainment/detrainment effects, gravity wave generation, and breakdown of steady-state solutions (instability). A numerical approach will also be employed to study the nature of the instability without the similarity constraint. Third, the Principal Investigator will conduct direct and large-eddy numerical simulations to investigate heat and momentum transfer properties of turbulent katabatic/anabatic flows. Obtained analytical and numerical solutions will be used for scale analyses of slope flows and design of parameterizations for the slope-flow related heat and momentum transport processes in climate and weather prediction models. Intellectual merit: Analytical methods and advanced numerical techniques will be brought together to bear synergistically on a broad class of katabatic/anabatic flows associated with variety of dynamic and thermodynamic forcings. Such flows are of fundamental scientific interest and are also important for a number of atmospheric applications described above. New knowledge regarding the structure, stability, and parameter dependencies of these flow types will be established. Broader impacts: This knowledge will be used to parameterize physical processes in katabatic/anabatic flows. Such parameterizations may prove valuable in weather prediction and climate models, where treatment of stratified flows above sloping terrain is fraught with difficulties. The study will provide a superb opportunity for graduate student training in analytical techniques and advanced numerical methods in a modern meteorological context, and will be used for extensive promotion of these techniques among underrepresented student groups.

下降流和上升流（风）基本上可以描述为在分层环境中沿着冷却/加热的倾斜表面的湍流自然对流。 它们普遍存在于所有纬度的复杂地形区域。 在盆地基本上不受天气影响的地区，这些流动是当地天气的组成部分。 即使有较强的天气强迫，明显的斜坡流信号往往是明显的。 持续的下降风是地球上像格陵兰岛和南极洲这样的广大地区的典型现象，并在区域气候中发挥着重要作用。 在横跨盆地的高度工业化/人口稠密地区（如洛杉矶和凤凰城），这些当地风对能源使用、能见度、雾的形成和污染物的扩散起着重要的控制作用。 即使在最理想化或最基本的形式下，斜坡流也将大气动力学中两个众所周知的困难方面：湍流和自然对流混为一谈。 虽然已经取得了很大的进展，在概念上的理解和数值模拟这样的流，长期存在的困难与稳定分层流的湍流建模，和各种流的相互作用，可以发生复杂的地形和表面的不均匀性（例如，从不规则的雪/冰/土壤覆盖，云量，地形阴影，和土地利用）使坡面流动力学的研究丰富的领域。本研究将集中在三个方面的下降/上升流在分层环境。首先，首席研究员将进行理论分析的斜坡流引起的不均匀的表面浮力强迫，其中经典的普朗特斜坡流模型将通过空间相似性约束扩展到包括不均匀的斜坡浮力，跨坡流，外部压力梯度，环境风和科里奥利力的影响。 其次，将使用三维数值模拟来测试相似模型的稳健性，特别是关于边界层厚度、流动强度、卷吸/分离效应、重力波生成和稳态解的崩溃（不稳定性）。 一个数值方法也将被用来研究不稳定的性质，没有相似性约束。第三，首席研究员将进行直接和大涡数值模拟，以研究湍流下降/上升流的热量和动量传递特性。所获得的解析解和数值解将用于坡面流的尺度分析以及气候和天气预测模式中与坡面流有关的热量和动量输送过程的参数化设计。智力优点：分析方法和先进的数值技术将汇集在一起，协同承担与各种动态和热力学强迫相关的下降/上升流的广泛类别。这种流动具有基本的科学意义，并且对于上述许多大气应用也很重要。将建立有关这些流动类型的结构、稳定性和参数依赖性的新知识。更广泛的影响：这方面的知识将被用来参数化下降/上升气流中的物理过程。这样的参数化可能被证明是有价值的天气预报和气候模式，在处理以上的倾斜地形的层流充满了困难。这项研究将提供一个极好的机会，研究生培训的分析技术和先进的数值方法在现代气象学的背景下，并将用于广泛推广这些技术之间的代表性不足的学生群体。