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Eugene M. Wilkins

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Eugene M. Wilkins

Eastern Idaho's Snake River Plain and that portion of the Continental Divide bordering it to the north comprise a topographic feature that provides an interesting local wind phenomenon. A sloping discontinuity surface is produced in a zone of conflict between slope and valley winds. The incursions of the front at the National Reactor Testing Station have become the subject of investigation because of their effect on the dispersion of stack effluents

Photographs are presented showing the effect of the frontal shear on a stack plume, smoke released at the ground, and a debris cloud from an experimental explosion. These photographs give an indication of the circulation pattern in the vicinity of the front. In addition, data from a network of recording stations, instruments on a 250-ft tower, and low-level wind and temperature soundings have been used to establish the circulation model.

Information is presented to show seasonal and diurnal effects, and also the influence of major pressure systems on the front phenomenon.

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Eugene M. Wilkins

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Formulas are derived, and their characteristics examined, for the purpose of optimizing objectively contoured patterns of air pollution concentrations where the diffusion equation is used as a dynamical constraint in the interpretation of network observations. The low-pan filter characteristics of the method are also demonstrated. An adjustment routine equation is derived for optimally correcting continuity discrepancies between successive isopleth patterns, such as might be computed for an automatic display system. Analytical expressions are obtained which predict the degree of improvement expected in practical applications where discrepancies occur in the analysis due to the natural periodic concentration variations which occur at monitoring stations. A sample calculation shows that the mean square residual error over a region can be reduced to less than 10% of its original magnitude when the adjustment routine is applied with a realistic set of meteorological parameters.

Such adjustment routines can be programmed into a computerized objective analysis method, and thus they can be applied with a high degree of automation and efficiency.

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Eugene M. Wilkins

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Eugene M. Wilkins

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A method is proposed whereby the Sutton-type diffusion coefficients appropriate for the instantaneous source may be estimated from observations of dissipation times for smoke puffs generated by standard gunpowder charges. It is logical to base the determination of these coefficients on observations of the spreading of smoke, especially if the technique is simple, inexpensive and subject to standardization.

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Eugene M. Wilkins

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The effect on instantaneous source diffusion of initial source size and diffusing time are studied from observations on the rate of separation of pairs of “zero lift” balloons.

The data indicate that the similarity concept of eddy diffusion is applicable for the scales of diffusion on the order of several minutes, and for distances of several kilometers, thus covering the region of many practical applications.

These findings provide some interesting information about the magnitude of the time dependency of the separation rate in the atmosphere. The rate of eddy energy dissipation calculated for a group of 10 runs was 70–200 cm2 set−3.

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Eugene M. Wilkins

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Eugene M. Wilkins

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Chris J. Diamond and Eugene M. Wilkins

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A simulation of tornadoes translating over the ground was carried out in a modified Ward simulator. The purpose was to investigate the effects of translation on tornado dynamics. The results are as follows:

• Secondary vortexes were found to be generated by the relative motion between the main vortex and rough “ground.” The secondary vortexes trail the primary vortex. Apparently they feed off the energy of the primary vortex, and achieve a momentary transition state from a single vortex to multiple vortexes.

• The core radius increases with swirl ratio and decreases with surface roughness. Translation causes a local increase in swirl ratio, increasing the core size over that of a stationary vortex.

• The central pressure drop increases with swirl ratio during translation. Translation also causes a steeper pressure gradient on the trailing side of the vortex core. A similar characteristic tilt on the trailing side of the pressure profile has been noted on barograms for real tornadoes.

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Eugene M. Wilkins and Chris J. Diamond

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Experimental data and theory suggest that certain convection cell scale factors must be specified for correct interpretation of tornado simulations. The most important nondimensional number appears to be the ratio of convection cell depth (relating to height of vortex terminal region) to radius of the updraft. This scale factor has been ignored by most investigators, but it is especially important when comparing experimental results between two simulators or when relating simulator results to real tornadoes. Implications are discussed for possible cell geometry effects on tornadoes.

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