SURFACE-ATMOSPHERE INTERACTION: THE IMPACT OF BUOYANCY AND HETEROGENEITY

Abstract

Surface-atmosphere interaction has significant impacts on atmospheric boundary layer dynamics and weather and climate variability. In this thesis, the effect of buoyancy and heterogeneity on surface-atmosphere interaction is examined using a combination of analytical, numerical and experimental approaches. The thesis is broadly separated into two parts: the first part focuses on the buoyancy effect (Chapters 2, 3 and 4) and the second part focuses on the heterogeneity effect (Chapters 5, 6, 7).

In the first part, the buoyancy is shown to induce dissimilarity between turbulent transports of momentum and scalars under unstable conditions. Under close-to-neutral but unstable conditions, dissimilarity between two scalars (i.e., temperature and water vapor) is also observed. The dissimilarity between momentum and scalars is linked to a change in the topology and scale of turbulent eddies. The length scale of the temperature profile becomes comparable to the length scale of a turnover eddy under unstable condition while the length scale of velocity profile is an order-of-magnitude larger that the length scale of the turnover eddy. The dissimilarity between temperature and water vapor is caused by large-scale processes such as advection or entrainment.

The second part of the thesis is rooted in urban environments and relies significantly on the Weather Research and Forecasting (WRF) Model. In particular, the parameterization of surface heterogeneity effects in the urban canopy model (UCM) is improved for studying various urban issues including the urban heat island (UHI) effect, the interaction between UHI and heat waves (HWs), as well as UHI mitigation. Results indicate a correct parameterization for the surface heterogeneity effect in urban areas is crucial for modeling UHI. The sub-grid scale variability of land use/land cover is also examined using the Noah land surface model. It is found that including the sub-grid scale variability is important for capturing the surface-atmosphere interaction over heterogeneous surfaces. The sub-grid scale variability of land surface characteristics also affects atmospheric boundary layer dynamics and rainfall patterns.