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.
