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

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

The oceanic phenomenon of upwelling along the Oregon coast is examined. Upwelling in both the open ocean and coastal regions is discussed. An idealized model is used, envisaging the ocean off Oregon to consist of homogeneous surface and deep layers separated by a pycnocline. The equations of motion are solved to yield the vertical velocity at the base of the surface layer. A comparison is made between the model and results inferred from hydrographic data. In the open ocean region qualitative agreement is observed between the wind stress curl and the depth of the surface layer. Geostrophic meridional transports relative to the 1000 decibar surface were computed and found to be of the order of the uncertainty. In the coastal upwelling region surface layer zonal transports were computed from the meridional component of the mean wind stress and compared with values inferred from oceanographic data. Coastal upwelling along the Oregon coast is clearly associated with the northerly (longshore) component of the wind stress. / Graduation date: 1964

Graduation date: 1999

We report upon an experimental study of internal gravity waves generated by the large-amplitude vertical oscillations of a circular cylinder in uniformly stratified fluid. Quantitative measurements are performed using a modified synthetic schlieren technique for strongly stratified solutions of NaCl or NaI. Oscillatory turbulent patches that develop around the cylinder are found to be the primary source of the observed quasi-monochromatic wave beams whose characteristics differ from theoretical predictions and experimental investigations of waves generated by small-amplitude cylinder oscillations. Over long times the waves break down into turbulence that is examined quantitatively through conductivity probe measurements and qualitatively through unprocessed synthetic schlieren images. Based on observations of the location of wave breakdown we determine that the likely mechanism for breakdown is through parametric subharmonic instability. This conclusion is supported by fully nonlinear numerical simulations of the evolution of a temporally monochromatic internal wave beam.

Boundary layer (BL) stratocumulus clouds are an important factor in the earth's radiation budget due to their high albedo and low cloud top heights. Continental BL stratocumulus clouds are closely coupled to the diurnal cycle and the turbulence in the BL affecting the surface energy and moisture budgets. In this study the turbulence and mass-transport structures in continental BL stratocumulus clouds are studied using data from the Atmospheric Radiation Measurements (ARM)'s Southern Great Plains (SGP) observing facility located at Lamont, Oklahoma. High temporal (4 sec) and spatial (45 m) resolution observations from a vertically pointing 35 GHz cloud Doppler radar were used to obtain the in-cloud vertical velocity probability density function (pdf) in the absence of precipitation size hydrometeors. A total of 70 hours of radar data were analyzed to report halfhourly statistics of vertical velocity variance, skewness, updraft fraction, downdraft and velocity binned mass-flux at five cloud depth normalized levels. The variance showed a general decrease with increase in height in the cloud layer while the skewness is weakly positive in the cloud layer and negative near cloud top. The updraft fraction decreases with height with the decrease mainly occurring in the upper half of the cloud layer. The downdraft fraction increases with decrease in height with the increase being almost linear. The velocity of eddies responsible for maximum mass-transport decreases from of 0.4 ms-1 near cloud base to 0.2 ms-1 near cloud top. The half-hour periods were then classified based on the surface buoyancy flux as stable or unstable and it was found that the variance near cloud top is higher during the stable periods as compared to the unstable periods. Classification was also made based on the cloud depth to BL depth ratio (CBR) being greater or less than 0.3. The variance profile was similar for the classification while the skewness was almost zero during periods with CBR less 0.3 and positive during periods with CBR greater than 0.3. A 14 hour period of stratocumulus cloud on March 25, 2005 was analyzed to study the diurnal changes in the turbulence structure and mass transports. The variance near cloud base during the day time when the BL turbulence is primarily due to surface buoyancy production was higher than during the nighttime when the BL turbulence is driven by radiative cooling near the cloud top. Output from a one dimensional radiative transfer model was analyzed to study the vertical structure of the radiative fluxes. A radiative velocity scale analogous to the surface convective velocity scale is proposed to assess the relative importance of radiative cooling near cloud top in generating turbulence compared with the surface buoyancy production. An attempt was also made to calculate the hourly liquid water flux by combining the high temporal resolution (20 sec) liquid water content estimates from the radar reflectivity and a microwave radiometer with the radar observed vertical velocity. The liquid water flux was found to peak at a level below the cloud top and show a divergence with height that was similar to that from model simulations.

In an effort to investigate the role of turbulence in near-forward scattering, laboratory measurements of scattering on turbulent flow were carried out in a Rayleigh-Bénard convective tank. Particle Image Velocimetry and profiling thermistor temperature measurements are used to characterize the turbulent flow through determination of the large scale flow features, turbulent kinetic energy dissipation rates, and thermal dissipation rates. Polarized diffractometer measurements allow for determination of the turbulence-induced depolarization rate, which is comparable to that observed with polarimetric lidar. Measurements were made over a range of turbulent strengths, with Rayleigh number between 10^8 and 3*10^9, and with turbulent parameters corresponding to those characteristic of the oceanic mixed layer. Results show that the turbulence-induced depolarization rate is indirectly proportional to the strength of the turbulent flow, suggesting that light beam depolarization from turbulent flow may contain useful information regarding the smallest length scales of turbulent flow.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oregon Graduate Center, 1980.

Thesis (Ph. D.)--Oregon Graduate Center, 1976.