Approved for public release; distribution is unlimited / The horizontal separations between convective thermal plumes, and features within a thermal plume, were determined through the use of an acoustic sounder, an anemometer and extensive data analysis. The mean, standard deviation, median and mode were calculated for the computed correlation lengths of the acoustic sounder data sampled in time intervals of 2, 5 and 10 minutes. The data sampled at 2 and 5-minute intervals emphasized features within an individual thermal plume. The mean correlation distances found for 2 and 5-minute intervals were 81 meters Å 70 meters and 89 meters Å 72 meters, respectively. Their medians were 61 meters and 69 meters; and their modes were 41 meters and 50 meters, respectively. The 10-minute time interval statistics used a low pass filter to emphasize larger scale features. The mean correlation length was 494 meters Å 373 meters, the median was 391 meters and the mode was 316 meters. These distances represent the distance between the center of a plume and the center of a quiet region adjacent to that plume. / Captain, United States Army

Globally intermittent turbulence is characterized by sudden switching from significant turbulence to weak turbulence and back on time scales ranging from seconds to tens of minutes as opposed to microscale intermittency, which is due to organization of small scale gradients by individual eddies on scales as small as the Kolmogorov microscale. This thesis examines globally intermittent turbulent atmospheric data by a conditional analysis technique. The conditional analysis separates the stronger turbulence sections of data from the weak sections and analyzes each type separately. This analysis is applied to two different sources of global intermittency. One case arises from the undulating structure of the top of a convective internal boundary layer that was forming due to a cool marine boundary layer being modified by a sun-heated beach. The other case is nocturnal boundary layer intermittency, the causes of which are not well known. When applied to the top of the convective internal boundary layer, the conditional analysis performs well in that a turbulent kinetic energy budget can be balanced. Conventional analysis of the same data is unsatisfactory. The conditional analysis improves the behavior of relationships for nocturnal intermittency, especially in that it reduces non-stationarity, but it does not explain all the scatter in the data. This may be due to the large role of self-correlation in the traditional presentation of the data. / Graduation date: 2003

Thesis (M.S. in Combat Systems Technology)--Naval Postgraduate School, December 2003. / Thesis advisor(s): D.L. Walters, D.K. Miller. Includes bibliographical references (p. 35-36). Also available online.

Thesis (M.S. in Space System Operations)--Naval Postgraduate School, Sept. 2004. / Thesis advisor(s): D.L. Walters, R.C. Olsen. Includes bibliographical references (p. 35). Also available online.

At the International Comparison of Turbulence Measuring Instruments, 1970, velocity components and momentum flux measurements were compared using propeller-type Fluxatrons (Hicks, 1970) and sonic anemometers from Kaijo-Denki, Japan and the Institute of Atmospheric Physics, U.S.S.R. There were distinct differences found in the measurements of the vertical velocity from the propeller sensors. The propeller's momentum flux measurements computed from its velocity components were also different. The U¹ propeller was found to be linear for lower frequencies with an associated distance constant of about 7 metre. Measurement of the variance of U¹ for f < 0.16 hz. showed the U¹ propeller in excess of both sonics by 20%. However, with the propeller's high frequency loss beyond f = 0.2 hz. the discrepancy was reduced to only an 8% excess for .00055 hz. < f < 10.8 hz. The W¹ propeller response was non-linear and had an upper cut-off frequency of 1hz. Because of its non-linear response and stalling characteristics at low wind speeds and also its high frequency cut-off the W¹ propeller was observed to measure only about 50% of the total fluctuating W¹ energy available. Analysis of the sonic cospectra of momentum showed that significant contributions to the momentum flux were to be found in the frequency domain 0.001 hz. < f < 5.0 hz. The combined response effects of the propeller were enough to reduce the Fluxatron’s estimate of this momentum flux by 32.5%. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The objective of this study was to investigate the turbulent transfer mechanisms near the surface. Direct measurements of the turbulent fluxes of momentum, heat, and moisture were made in the atmospheric surface layer: principally, 2 m above a grass surface at Ladner, Canada, and for comparison 8 m above the Atlantic Ocean near Barbados. The spectral correlation coefficients were considered to be a measure of the transfer efficiency as a function of scale size. For momentum transfer the efficiency decreased at all scales as instability increased. It was postulated that this was due to greater amounts of momentum being transferred in bursts of short duration, thus making the spectral correlation coefficient, averaged over sufficient time, smaller. The Ladner results for heat transfer showed that its transfer efficiency increased at all scales when instability increased. The ratios of the transfer efficiency of heat to that of momentum were greater than 1 for most scales, even for near neutral stratifications, and increased to between 2 and 3 for more unstable conditions. The efficiency of moisture transfer, when moisture is a passive scalar, was usually smaller than that for heat transfer and was found to depend on the correlation between moisture fluctuations and those of temperature, which is the active scalar. The results from Barbados pointed out two main differences between the subtropics and mid-latitudes: that the temperature spectrum is much narrower in bandwidth and that the humidity fluctuations make an equally important contribution to buoyancy. These features are reflected in the transfer mechanisms. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Two systems for remote measurements of the air-sea fluxes of momentum, sensible heat and moisture during moderate to strong winds are described. One employs the dissipation method and the other the Reynolds flux or eddy correlation method. A modified Gill propeller-vane anemometer is the velocity sensor and a method of resolving the vertical velocity component, that accounts for the propeller's non-cosine behavior and avoids its non-linear operating region, is derived. The dynamic responses of the sensors are found from measurements in the actual turbulent conditions of the flux measurements. The results of an experiment on the Bedford tower, a stable platform moored in 59m of water 10 km offshore, are presented. Spectra, cospectra, turbulence statistics and transfer coefficients are calculated from the Reynolds flux velocity and temperature data and found to be comparable to previously reported values. Simultaneous dissipation and Reynolds flux estimates of both the momentum and sensible heat fluxes in up to 20 m/s winds are shown to be in excellent agreement. Also presented are the results of a second experiment where the systems were deployed on the weathership CCGS Quadra. A comparison of ship and tower drag coefficients from the dissipation system, demonstrates that the Bedford tower is essentially an open ocean site. The neutral drag coefficient, CDN, is found, on average, to be nearly constant at 1.14x10⁻³ for winds between 4 and 10 m/s and to increase almost linearly to about 2.18x10⁻³ at 26 m/s. No variation with either fetch (greater than 10 km) or stability is observed. Dissipation estimates of the sensible heat flux from a wide range of conditions are presented. The neutral transfer coefficient, CTN, is found, on average, to vary from about 0.69x10⁻³ in stable stratification to 1.08x10⁻³ in the unstable case. An increase in CTN with increasing wind speed is suggested by only some of the data. Time series of the fluxes are used to investigate additional sources of variation in the transfer coefficients. Their statistical variability about a running mean is seen to be about 10%. Evidence is presented that indicates that persistent departures from average values are related to sea surface conditions. CDN is observed to be significantly smaller, on average, during rising winds than during falling winds or after a change in wind direction. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). "November 24, 2009." Includes bibliographical references (p. 325-330). Also available via the World Wide Web.

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published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy