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Steven R. Hanna
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Steven R. Hanna

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Observations of the relative diffusion of 13 sets of tetroon pairs in the mixed layer during convective conditions in eastern Tennessee are reported. The root-mean-square separation S is proportional to time t raised to a power of 1 for times from 2 to 30 min and a power of 0.75 for times from 30 to 100 min. On the average, the observations are satisfied by the approximation dS/dtσ y where σ y is the standard deviation of the lateral wind speed fluctuations, as sensed by the tetroon.

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Steven R. Hanna

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Steven R. Hanna

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Formulas for the variation with height of the buoyancy, volume, and water vapor fluxes from large wet cooling towers are derived. The simple formulas developed by Briggs are suggested for estimating plume rise, if the possibility of the release of latent heat is accounted for in the definition of the initial buoyancy flux. The probability of whether condensation will occur is sensitive to small variations in moisture content and temperature of the environment. Verification of the theory is hampered by the scarcity of adequate measurements of cooling tower plumes.

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Steven R. Hanna

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A one-dimensional plume and cloud growth model is applied to four months of radiosonde observations from Nashville, using as initial conditions the plume from single large cooling towers with waste heat outputs of 103, 104 and 105 MW, and a complex of cooling towers with a total waste heat output of 105 MW. Estimates of average annual plume rise from the four energy sources are 580,1180,2460 and 780 m, respectively.

The predicted plume rise, visible plume length and cloud formation are given as functions of time of day, year and weather type. For example, a cloud forms at the top of the plume from the 103 MW tower in 65% of the morning soundings during which ground level fog was observed. A cloud is predicted to occur 95% of the time at the top of the plume from the single 105 MW tower. It is found that if the towers in an energy center are separated by a distance greater than the average plume rise from one tower, then plume merging is minimized. Observations from TVA's Paradise steam plant are used to test the predictions of visible plume length from a single 103 MW tower.

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Steven R. Hanna

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Hourly ground-level concentrations of SF6 at downwind distances ranging from 0.5 to 50 km were observed by the Electric Power Research Institute (EPRI) on dense monitoring networks around power plants at Kincaid, Illinois, and Bull Run, Tennessee. Sigma y on given sampling arcs was estimated by a robust procedure. Over 160 h of data are available from monitoring arcs located at about five downwind distances, which show that σy is close to linear with downwind distance, x. During unstable conditions, σy u/w * x=0.6. When all the data are plotted together, the following empirical equation is valid:

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Steven R. Hanna

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Steven R. Hanna

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The linear relationship u′(t + τ) = u′(t)R(τ) + u″(t) is shown to be approximately valid for Lagrangian and Eulerian wind speed observations in the planetary boundary layer, where t represents any time and t + τ is some later time, u′ is the turbulent wind speed fluctuation, R(τ) the autocorrelation coefficient, and u″ a random wind speed component assumed to be independent of u′. Eulerian wind data from the Minnesota boundary layer experiment and Lagrangian wind data from tetroon trajectories near Las Vegas and Idaho Falls are analyzed. At extreme values of u′(t) for the Eulerian data, u′(t + τ) tends to be slightly less than that predicted by the above relationship. An application of this formula to the calculation of diffusion yields results in agreement with Taylor's theory.

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Steven R. Hanna

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It is suggested that helical roll vortices in the atmosphere are responsible for the formation of the longitudinal sand dunes that cover over half of the area of the large deserts of the world. The dunes are aligned in the direction of the prevailing wind and are spaced ∼2 km apart. Observations in the atmosphere and in the laboratory, and hydrodynamic stability theory, indicate that dominant forms of motion in the boundary layer of the atmosphere are counter-rotating helical roll vortices aligned along the wind and having diameters approximately equal to the thickness of the boundary layer. The necessary conditions for the formation of these roll vortices are fulfilled over large deserts and their spacings agree with the observed spacings of the dunes.

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Steven R. Hanna

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There is much evidence in the literature for the presence of mesoscale lateral meanders in the stable nighttime boundary layer. These meanders result in relatively high lateral turbulence intensities and diffusion rates when averaged over an hour. Anemometer data from 17 overnight experiments at Cinder Cone Butte in Idaho are analyzed to show that the dominant period of the mesoscale meanders is about two hours. Lidar cross-sections of tracer plumes from these same experiments show that the hourly average σ y is often dominated by meandering. Since meandering is not always observed for given meteorological conditions, it is suggested that nighttime diffusion cannot be accurately predicted without using onsite observations of wind fluctuations. In case no turbulence data are available, an empirical formula is suggested that predicts the hourly average lateral turbulence intensity as a function of wind speed and hour-to-hour variation in wind direction.

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