CAREER: A Universal Framework for Large-Eddy Simulation of Atmospheric Boundary Layer Flow Over Complex Terrain

大气边界层(ABL)通过天气和空气质量直接影响人类生活。关于这个薄薄的大气层还有很多有待了解的地方，部分原因是它受到地形和地表特征变化的强烈影响。这些变化可能导致热力强迫流动，如平静条件下的谷风和大风条件下的大气层旋风和地形阻塞的背风波。了解这种流动特征的物理动力学需要详细的现场观测和高分辨率的数值模拟。大涡模拟(LES)是模拟ABL流动的最有前途的数值技术之一，因为它允许通过空间滤波来控制湍流的长度尺度，从而将大的、可分辨的运动从子过滤器尺度的湍流运动中分离出来。虽然大涡模拟主要用于理想流动条件的模拟，但它有可能在复杂地形上的ABL研究中得到普遍应用。智力优势：这项研究将调查关键的创新步骤，以扩展LES的可扩展性，使其可以从区域到非常精细的尺度使用。这将使LES有效地应用于复杂地形上的流动，并导致对边界层流动过程的更深入的了解。控制湍流长度尺度，改善侧边界强迫，生成集合模拟，减少由于次网格表面粗糙度参数化和陡峭地形表示而产生的数值误差的新策略将为复杂地形上的一般大涡模拟应用创造一个通用的框架。这一框架将与观测数据分析结合使用，以研究地形引起的流动特征，如山波和旋风以及山谷风环流。PI在陡峭山区的边界层流动以及为大涡模拟开发数值方法和湍流闭合方案方面拥有丰富的经验。提出了一个综合的教育和推广计划，通过一个互动的模拟网站，激发K-12学生和公众对大气边界层现象的认识，并为本科生和研究生提供数值模拟经验。学生将与加州大学伯克利分校的劳伦斯科学馆(LHS)一起参加这一公共推广计划，通过暑期助学金和一门新的大涡模拟研究生课程直接与在线展览相结合。这门课程还将通过提供数值方法的实践培训来加快研究生的研究进程。更广泛的影响：拟议的大涡模拟通用框架将通过从中尺度到城市尺度的嵌套模拟，实现所有尺度上的流动特征的无缝集成。通过这个新的数值框架获得的关于复杂流动的新知识将极大地改进用于预测天气、空气污染、污染物扩散和区域气候的模型。此外，对山区可能发生的大气环流和强烈重力波的洞察将对航空安全产生重要影响。在高级研究数值模型中实施的新计算方法将通过不断公开发布代码更新而接触到广泛的用户社区。将通过这项研究培训两名研究生，并通过加州大学伯克利分校的一流项目为未被充分代表的少数族裔工程学生提供两个本科生研究助学金。研究成果将通过期刊出版物和会议报告进行传播。拟议的教育工具的可用性将通过劳伦斯科学堂(LHS)的主要网站、PI的实验室和部门网站以及美国气象学会公报上的一篇文章进行宣传。互动建模网站有可能接触到数以千计的个人，并可在所有年龄段的课堂环境中使用，向学生介绍天气过程和数值建模。数百名额外的参观者，主要是K-12的学生，将参加由PI和学生提供的LHS博物馆地板演示。

The atmospheric boundary layer (ABL) directly influences human life through weather and air quality. Much remains to be understood about this thin atmospheric layer, partly because it is strongly affected by variations in topography and land-surface characteristics. These variations can lead to thermally-forced flow such as valley winds under calm conditions and atmospheric rotors and lee waves under strong winds with topographic blocking. Understanding the physical dynamics of such flow features requires detailed field observations and high-resolution numerical simulations. Large-eddy simulation (LES) is one of the most promising numerical techniques for modeling ABL flow because it allows control of turbulent length scales through spatial filtering to separate large, resolved motions from subfilter-scale, turbulent motions. Although primarily used for simulations of idealized flow conditions, LES has the potential to become universally applicable to ABL studies over complex terrain. Intellectual merit: This research will investigate key, innovative steps to extend the scalability of LES so it can be used from regional to very fine scales. This will allow LES to be effectively applied to flow over complex terrain and lead to greater insight into boundary layer flow processes. New strategies to control turbulent length scales, improve lateral boundary forcing, generate ensemble simulations, and reduce numerical errors due to subgrid surface roughness parameterizations and representation of steep topography will create a universal framework for general LES applications over complex terrain. This framework will be used together with observational data analysis to study terrain-induced flow features such as mountain waves and rotors and valley wind circulations. The PI has extensive prior experience with boundary layer flows over steep, mountainous terrain as well as with developing numerical methods and turbulence closure schemes for LES. An integrated education and outreach program is proposed to excite K-12 students and the general public about atmospheric boundary layer phenomena through an interactive modeling website and to provide numerical modeling experience to both undergraduate and graduate students. Students will participate in this public outreach program with UC Berkeley's Lawrence Hall of Science (LHS) through summer assistantships and a new graduate course on large-eddy simulation that will be directly coupled to the online exhibit. This course will also accelerate graduate research progress by providing hands-on training in numerical methods. Broader impacts: The proposed universal framework for LES will make possible seamless integration of flow features at all scales through nested simulations from the mesoscale to the urban scale. New knowledge of complex flows gained with this new numerical framework will dramatically improve models used to predict weather, air pollution, contaminant dispersion, and regional climate. Furthermore, insights into atmospheric circulations and intense gravity waves that can occur in mountainous areas will have important implications for aviation safety. New computational methods implemented in an advanced research numerical model will reach a broad community of users through continued public releases of code updates. Two graduate students will be trained through this research and two undergraduate research assistantships will be provided for under-represented minority engineering students through the SUPERB program at UC Berkeley. Research results will be disseminated through journal publications and conference presentations. The availability of the proposed educational tools will be advertised through the main Lawrence Hall of Science (LHS) website, through the PI's lab and department websites, and through an article in the Bulletin of the American Meteorological Society. The interactive modeling website has the potential to reach thousands of individuals and can be used in classroom settings at all age levels to introduce students to weather processes and numerical modeling. Hundreds of additional visitors, primarily K-12 students, will attend LHS museum floor demonstrations given by the PI and students.