Analytical and Numerical Studies of Katabatic and Anabatic Flows in Stratified Atmospheric Environments

University Of Oklahoma Norman Campus, Norman OK

Investigators

Abstract

Katabatic and anabatic flows (winds) can be described, most basically, as turbulent natural convection flows along cooled/heated sloping surfaces in a stratified environment. They are ubiquitous in regions of complex terrain at all latitudes. In regions where basins are largely sheltered from synoptic effects, these flows are the building blocks of local weather. Even with a stronger synoptic forcing, pronounced slope flow signals are often apparent. Persistent katabatic winds are typical for vast areas of the earth like Greenland and Antarctica, and play an important role in the regional climate. In heavily industrialized/populated regions extending across basins (like Los Angeles and Phoenix), these local winds exert major controls over energy usage, visibility, fog formation, and pollutant dispersion. Even in their most idealized or elemental forms, slope flows conflate two notoriously difficult aspects of atmospheric dynamics: turbulence and natural convection. Although much progress has been made in the conceptual understanding and numerical modeling of such flows, long-standing difficulties with turbulence modeling in stably-stratified flows, and the variety of flow interactions that can occur with complex topography and surface inhomogeneity (e.g. from irregular snow/ice/soil cover, cloudiness, topographic shading, and land use) make slope flow dynamics a rich area of study. This research will focus on three aspects of katabatic/anabatic flows in stratified environments. First, the Principal Investigator will conduct a theoretical analysis of slope flows induced by inhomogeneous surface buoyancy forcing, in which the classical Prandtl slope flow model will be extended via a spatial similarity constraint to include effects of inhomogeneous slope buoyancy, cross-slope flow, external pressure gradient, ambient wind, and Coriolis force. Second, three-dimensional numerical modeling will be used to test the robustness of the similarity model, specifically with regard to boundary layer thickness, flow intensity, entrainment/detrainment effects, gravity wave generation, and breakdown of steady-state solutions (instability). A numerical approach will also be employed to study the nature of the instability without the similarity constraint. Third, the Principal Investigator will conduct direct and large-eddy numerical simulations to investigate heat and momentum transfer properties of turbulent katabatic/anabatic flows. Obtained analytical and numerical solutions will be used for scale analyses of slope flows and design of parameterizations for the slope-flow related heat and momentum transport processes in climate and weather prediction models. Intellectual merit: Analytical methods and advanced numerical techniques will be brought together to bear synergistically on a broad class of katabatic/anabatic flows associated with variety of dynamic and thermodynamic forcings. Such flows are of fundamental scientific interest and are also important for a number of atmospheric applications described above. New knowledge regarding the structure, stability, and parameter dependencies of these flow types will be established. Broader impacts: This knowledge will be used to parameterize physical processes in katabatic/anabatic flows. Such parameterizations may prove valuable in weather prediction and climate models, where treatment of stratified flows above sloping terrain is fraught with difficulties. The study will provide a superb opportunity for graduate student training in analytical techniques and advanced numerical methods in a modern meteorological context, and will be used for extensive promotion of these techniques among underrepresented student groups.