Origin and Transport Properties of Coherent Structures in the Planetary Boundary Layer

本研究的目的是利用瞬态发展理论研究行星边界层中相干结构的起源和输运性质。先前关于该主题的理论工作仅限于对模态不稳定性的研究，这些研究证实，在对流不稳定条件下，通常显示为云街的卷形式的相干结构最有效地产生。最近对非分层实验室流动的瞬态非模态发展的研究表明，在没有模态不稳定的流动中，相干结构的发展是稳健的。在本项目中，瞬态发展理论将首次应用于对流稳定和不稳定粘性剪切流。导致最大能量增长的初始扰动将通过采用变分方法来确定。我们将研究这些扰动的结构和演化，以及它们对理查德森数、雷诺兹数和普朗特数的依赖。与二阶交换过程相关的输运性质也将被研究。由于结构随时间演化，二阶相关性将作为主导扰动从初始生长到最终衰变的整个生命周期的平均量来获得。这项研究解决了在NWP和气候模式中进一步理解示踪剂运输、海气相互作用、云街组织以及热量和动量参数化的重要问题。

The object of this research is the investigation of the origin and transport properties of coherent structures in the planetary boundary layer (PBL) using transient development theory. Previous theoretical work on this topic has been limited to the investigation of the modal instabilities and these studies confirm that coherent structures in the form of rolls, often revealed as cloud streets, are produced most efficiently under convectively unstable conditions. Recent work on transient non-modal development of unstratified laboratory flows demonstrates that coherent structures develop robustly in flows possessing no modal instabilities. In this project, transient development theory will be applied for the first time to convectively stable and unstable viscous shear flows. The initial disturbances that lead to the largest energy growth will be determined through the employment of a variational method. The structure and evolution of these disturbances will be studied, along with their dependence on the Richardson, Reynolds, and Prandtl number. Transport properties associated with the second order exchange process will also be studied. Because the structures evolve in time, the second order correlations will be obtained as mean quantities over the life cycle of the dominant perturbations from initial growth to ultimate decay. This study addresses issues important to further progress in understanding tracer transport, air-sea interaction, organization of cloud streets, and parameterization of heat and momentum in NWP and climate models.