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

最基本的描述是，在分层环境中，顺冷却/加热斜坡表面的湍流自然对流流动。它们在所有纬度的复杂地形地区普遍存在。在盆地基本上不受天气影响的地区，这些气流是当地天气的组成部分。即使有较强的天气强迫，明显的坡流信号也经常是明显的。持续的斜降风在地球上的大片地区如格陵兰岛和南极洲是典型的，在区域气候中起着重要作用。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），这些当地的风对能源使用、能见度、雾的形成和污染物的扩散起着主要的控制作用。即使在最理想或最基本的形式下，坡流也融合了大气动力学中两个众所周知的困难方面：湍流和自然对流。尽管在这类流动的概念理解和数值模拟方面取得了很大进展，但在稳定分层流动中湍流建模的长期困难，以及复杂地形和表面不均匀性（例如，不规则的雪/冰/土壤覆盖、云量、地形遮阳和土地利用）下可能发生的各种流动相互作用，使斜坡流动动力学成为一个丰富的研究领域。本研究将从三个方面探讨分层环境中渐退/渐退流动。首先，首席研究员将对非均匀表面浮力作用下的坡面流动进行理论分析，通过空间相似性约束对经典普朗特坡面流动模型进行扩展，包括非均匀坡面浮力、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鲁棒性，特别是关于边界层厚度、流动强度、夹带/夹带效应、重力波产生和稳态解的分解（不稳定性）。数值方法也将被用来研究没有相似约束的不稳定性的性质。第三，进行直接和大涡数值模拟，研究紊流的热动量传递特性。获得的解析解和数值解将用于坡流的尺度分析和设计气候和天气预报模型中与坡流相关的热量和动量传输过程的参数化。智力优势：分析方法和先进的数值技术将结合在一起，协同作用于与各种动力和热力学作用力相关的广泛的反/反流。这种流动具有基本的科学意义，对上述若干大气应用也很重要。将建立有关这些流型的结构、稳定性和参数依赖性的新知识。更广泛的影响：这方面的知识将用于参数化渐退/渐退流动中的物理过程。这种参数化可能在天气预报和气候模型中证明是有价值的，在这些领域，处理斜坡地形上的分层流动充满了困难。这项研究将为研究生在现代气象背景下进行分析技术和先进数值方法的培训提供极好的机会，并将用于在代表性不足的学生群体中广泛推广这些技术。

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.