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

小行星9310576 这项工作的目的是分析几个新的和现有的数据集的目标，提高我们的理解边界层流动的异质表面的响应范围从多个，定义明确，不连续性更复杂的表面异质性。 新的数据包括飞机，塔和有限的遥感观测，并允许详细检查类的异质性以前没有考虑。 其中一个目标是检查的面积平均表面通量的主要影响。 这些影响包括：1）与散射树、森林边缘和其他障碍物引起的压阻相关的动量通量的增强，2）表面条件变化下游过渡区的非平衡效应，3）与空间变率和通量与梯度之间的非线性关系相关的额外Reynolds项，以及4）中尺度运动的直接输送。 为了解决这个问题，将飞机在同一轨迹上重复运行所观察到的气流正式分解为湍流、瞬时中尺度运动和静止中尺度运动（主要与表面非均匀性相关）。 两个中尺度分量对湍流通量的调制将被详细考虑。 从更实际的角度来看，上述对面积平均通量的影响将隐含地纳入到有效粗糙度长度和面积平均通量对应的交换系数的计算中。 这些计算之前，将分析通量采样误差，其中将包括一些研究的技术估计通量误差。 建议的理论工作将仅限于解释中尺度环流在异质地形的几个现有的线性和非线性预测。 ***

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. ***