Turbulent Fluxes and their Relation to Surface Heterogeneity and Transient Mesoscale Motions

湍流通量及其与表面异质性和瞬态中尺度运动的关系

• 批准号: 9310576
• 负责人: Larry Mahrt
• 金额: $ 31.64万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1993
• 资助国家: 美国
• 起止时间: 1993-11-01 至 1998-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9310576&HistoricalAwards=false
• 关键词: Turbulent; Fluxes; their; Relation; Surface

9310576 Mahrt The objective of this work is to analyze several new and existing data sets toward the goal of improving our understanding of the response of boundary-layer flow to heterogeneous surfaces ranging from multiple, well defined, discontinuities to more complex surface heterogeneity. The new data include aircraft, tower and limited remote sensing observations and allow examination of classes of heterogeneity in detail not previously considered. One of the goals is to examine the main influences on the area averaged surface fluxes. These influences include: 1) enhancement of the momentum flux associated with pressure drag induced by scatter trees, forest edges and other obstacles, 2) non-equilibrium effects in transition zones downstream from changes of surface conditions, 3) extra Reynolds terms associated with spatial variability and the nonlinear relationship between fluxes and gradients and 4) direct transport by mesoscale motions. To approach this problem, the flow observed by repeated aircraft runs over the same track is formally decomposed into turbulence, transient mesoscale motions and stationary mesoscale motions (primarily associated with surface heterogeneity). The modulation of the turbulence flux by the two mesoscale components will be considered in detail. From a more practical point of view, the above influences on the area averaged flux will be implicitly incorporated into calculation of effective roughness lengths and exchange coefficients corresponding to the area averaged fluxes. These calculations will be preceded by an analysis of flux sampling errors which will include some research on the techniques for estimating flux errors. Proposed theoretical work will be limited to interpretation of the mesoscale circulations over heterogeneous terrain in terms of several existing linear and nonlinear predictions. ***

9310576 Mahrt 这项工作的目标是分析几个新的和现有的数据集，以提高我们对边界层流对异质表面（从多个、明确的不连续性到更复杂的表面异质性）响应的理解。 新数据包括飞机、塔台和有限的遥感观测数据，并允许对以前未考虑过的详细异质性类别进行检查。 目标之一是检查对面积平均表面通量的主要影响。 这些影响包括：1) 与分散树木、森林边缘和其他障碍物引起的压力阻力相关的动量通量增强，2) 地表条件变化下游过渡区的非平衡效应，3) 与空间相关的额外雷诺项变化性以及通量和梯度之间的非线性关系；4）中尺度运动的直接传输。 为了解决这个问题，飞机在同一轨道上重复运行所观察到的流动被正式分解为湍流、瞬态中尺度运动和静止中尺度运动（主要与表面不均匀性相关）。 将详细考虑两个介尺度分量对湍流通量的调制。 从更实际的角度来看，上述对面积平均通量的影响将隐式地纳入到面积平均通量对应的有效粗糙度长度和交换系数的计算中。 在进行这些计算之前，将对通量采样误差进行分析，其中包括对估计通量误差的技术进行一些研究。 拟议的理论工作将仅限于根据几种现有的线性和非线性预测来解释异质地形上的中尺度环流。 ***