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A baroclinic, convective mixed-layer was modeled, using water, in a laboratory convection tank identical to that used in the free convection study of Deardorff and Willis (1985). Baroclinicity and mean-flow shearing were achieved by tilting the tank by an angle of 1O⁰. The resulting mechanical-production rate of turbulence kinetic energy was comparable in magnitude to the buoyancy-production rate at mid-levels within the mixed-layer. Velocities were obtained by taking time-lapse photographs of neutrally-buoyant oil droplets suspended in the mixed-layer fluid. Variances and other statistical descriptors of the turbulence obtained from these velocities are presented in comparison to the free convection results of Deardorff and Willis (1985). The deviation of the present results from those of Deardorff and Willis (1985) are assumed to be related to the effects of mean-flow shearing and are explained wherever possible with the aid of an appropriate kinetic energy budget (kinetic energy, here, refers to the kinetic energy of the turbulence and is not to be confused with the kinetic energy of the mean-flow). The results indicate that a maximum in downstream horizontal kinetic energy at mid-levels within the mixed layer was generated by shear-production and, also, by conversion from vertical kinetic energy. In the lower mixed-layer, vertical kinetic energy was amplified by a mechanical-production term associated with the divergence of the mean vertical velocity. Total turbulence kinetic energy, normalized by the square of the convective velocity scale, was much larger at mid-levels than in Deardorff and Willis (1985) due to mechanical-production which is not accounted for by simple mixed-layer scaling. Horizontal turbulence structure was predominately controlled by convection while vertical turbulence structure was significantly altered by mean-flow shearing. / Graduation date: 1989

A two-scale approach for the turbulent mixing of momentum in an unstable stratified boundary layer is proposed in an attempt to eliminate existing inconsistencies between parameterized mixing of heat and momentum. The parameterization of the large eddy stress is suitable for simple boundary layer models where computational efficiency is important. We test the proposed formulation in a simple boundary layer model and compare predicted momentum profiles with Lidar mean momentum profiles from FIFE 1989. We examine the sensitivity of the proposed mixing scheme to baroclinicity. While the proposed two-scale approach is able to better predict observed conditions of well mixed momentum profiles, the complexity of momentum transport in baroclinic conditions is not well approximated. / Graduation date: 1994

An eigenvector analysis of the velocity-temperature correlation matrix is applied to clear-air turbulence measured by aircraft in the Bora. The eigenvectors are identified with the main eddies of the turbulence. This study attempts to infer the three-dimensional structure of these eddies. The results are compared with turbulent structures in the stable boundary layer. The turbulence in the strongly stratified boundary layer appears to be dominated by double roller eddies with their axes of rotation tilted in the shear direction. The clear-air turbulence shows a larger variety of motion types. / Graduation date: 1986

A shallow convection scheme is derived from several data sets (BOMEX, GATE, AMTEX, BLX83) and developed for the OSU 1-D boundary layer model. Results of the model structure and characteristics of the saturation point (SP) profile are compared against the constant cloud diffusivity scheme of Tiedtke (1983) and the ECMWF boundary layer parameterization scheme. The results indicate that the primary mechanism that transports moisture away from the lower boundary layer is the boundary layer turbulent flux and that the boundary turbulent mixing alone is capable of maintaining an apparent moisture source near the inversion. While the sensible heat flux over ocean becomes quite small after a few hours of model simulation, the virtual heat flux remains positive and the boundary layer remains in the unstable regime. / Graduation date: 1987

The influence of irregular terrain on the evolution of the daytime planetary boundary layer (PBL) and meso-β scale dry circulations is studied using two three-dimensional hydrostatic σ-coordinate models with different approaches for the PBL parameterizations; the 4-layer model uses the mixed-layer (bulk-layer) approach, while the 7-layer model adopts the eddy-diffusivity (multi-layer) approach. Numerical experiments are carried out under the conditions of a dry, sunny summer day with moderate prevailing westerly winds blowing over gently sloping idealized hills in a domain of 150 km on a side. The results from the two models are compared and their performances are evaluated. The behaviors of the mean PBL depth and inversion strength are analytically described using a simple one-point mixed-layer model. Counterclockwise rotation of the mean PBL winds with time observed in both model results can be explained only when the non-zero momentum flux at the PBL top is taken into account. However, stresses associated with entrainment at the PBL top are not sufficient to pull the cold air out of the valleys so as to result in breakup of the early morning stable layer, as is suggested in a previous study. The regions of weak winds that persist in the morning PBL are attributed largely to the baroclinic effect of horizontal variations of potential temperature θ in the PBL, while the effect of surface drag is quite small in these areas. Significant differences in the flow patterns near the surface in two results suggest the importance of the local pressure gradient force associated with terrain irregularities. The effect of horizontal θ advection is also significant in helping reduce the PBL θ anomalies and promote breakup of the stable layer. The well-mixed assumption generally applies quite well to the development of the θ profiles, while for momentum it seems valid only during the peak of convective mixing and the eddy-diffusivity approach is probably preferable for a better description of the low-level flows. The fields of the PBL top height obtained using different procedures in the two models are found to correspond fairly well to each other. Mass-flux convergence associated with terrain irregularities and resulting changes in the wind fields are shown to play a key role in the midday PBL height patterns. The development of the PBL structure as revealed by the θ cross sections obtained from either model corresponds favorably to that indicated by idealized cross sections previously constructed from observed data. The formation of a region of mass-flux convergence and accompanying updrafts near the surface on the leeward side of a mountain, processes which are likely to be important in terrain-induced cloud initiations, seem to be simulated. / Graduation date: 1985

The laminar-to-turbulent transition process in swept-wing boundary layers is often dominated by an inflectional instability arising from crossflow. It is now known that freestream turbulence and surface roughness are two of the key disturbance sources in the crossflow instability problem. Recent experimental findings have suggested that freestream turbulence of low intensity (less than 0.2%) may have a larger influence on crossflow instability than was previously thought. The present work involves experimental measurement of stationary and traveling crossflow mode amplitudes in freestream turbulence levels between 0.02% and 0.2%. A 1.83 m chord, 45-degree swept-wing model is used in the Klebanoff-Saric Wind Tunnel to perform these experiments. The turbulence intensity and length scales are documented. Although a significant amount of research on the role of turbulence has been completed at higher turbulence levels, comparatively little has been done at the low levels of the present experiments, which more closely reflect the flight environment. It is found that growth of the traveling crossflow mode is highly dependent on small changes to the freestream turbulence. Additionally, previously studied attenuation of saturated stationary disturbance amplitudes is observed at these low turbulence levels. The extent of laminar flow is also observed to decrease in moderate freestream turbulence.

Thesis (M.S. in Meteorology and Oceanography)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Shaw, W.J. Second Reader: Nuss, W.A. "September 1990." Description based on title screen as viewed on December 29, 2009. DTIC Identifier(s): Marine atmospheres, marginal ice zones, geostropic wind, atmospheric boundary layer, stratus clouds, cumulus clouds, stratocumulus clouds, wind velocity, temperature inversion, air ice interactions. Author(s) subject terms: Marginal ice zone. Includes bibliographical references (p. 45-46). Also available in print.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 125-136).

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 184-197).