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W. D. King

Abstract

It is shown that the trajectories of precipitation particles which grow via the riming process depend primarily on liquid water content and cloud depth, and not on the exact details of cloud temperature, crystalline shape, and graupel shape and size. Fall times for seeding at −15°C at an altitude of 5 km could be as long as 55 min. Particle masses cannot be calculated very precisely, mostly because of uncertainties in specification of the graupel shape and size. It is still possible, however, to develop general rules regarding cloud depth required for seeding, the much-used rule that cloud depth should exceed half the cloud-base height being a reasonable one to adopt.

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W. D. King

Abstract

The vapor field around an ice crystal growing on a membrane filter in a static diffusion chamber is modeled and the associated losses in deposition nuclei due to crystal-crystal vapor depletion calculated. The expression which is derived relates the depletion losses to the aerosol activity spectrum and the processing characteristics of the chamber, such as time constant, supersaturation and plate separation. In particular, it is suggested that depletion losses are affected most by changes in the time taken to reach the required supersaturation: with crystal-crystal depletion, a slow rise to the processing level increases the losses. The model, along with some of its underlying assumptions, is compared with experimental results using an AgI aerosol, and found to be in reasonable agreement. Some applications of the model to other types of filter processing chambers are also discussed, and a similar but untested model for depletion losses due to the presence of hygroscopic particles is given as an appendix.

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W. D. King

Abstract

The freezing rates of water droplets have been calculated. The interfacial position is specified as a power series in time, and expressions for determining the first five coefficients are given. The five–term series solution is compared with an exact numerical one for a particular case, and the agreement is within 1% during most of the freezing process. For small droplets, the solution reduces to a previously published one, and the results of experiments in which the freezing times of droplets were measured confirm this.

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W. D. King

Abstract

A potential-flow sink-source technique is used to model the flows around fuselage shapes. It is shown that the flow in any plane can be approximated reasonably well using an axisymmetric model of similar shape and that at a few fuselage radii from the nose the flow is determined principally by the size of the fuselage radius. Departures from the free-stream velocity are typically less than 10% and vary as the inverse square of the scaled distance from the nose. Analyses of water drop trajectories around three different aircraft shapes show that two of the more important features of the trajectories, the width of the shadow zone and the concentration enhancement factors, can be described quite generally in terms of a scaled fuselage radius and a parameter similar to the Stokes number. Thus the maximum width of the shadow zone is shown to be about one-fifth of the fuselage radius and occurs for a combination of particle size and aircraft speed for which the modified Stokes parameter has a value of about 6.

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W. D. King

Abstract

Earlier work that produced generalized rules for obtaining trajectories of water droplets moving around aircraft fuselages has been extended to cover the case for particles of arbitrary shape. The parameters determining the major features of the trajectories are the fuselage radius and a generalized Stokes number that can be used to calculate an equivalent water drop size for particles of arbitrary shape and density. As for water drops, the maximum width of the shadow zone for sampling the particles is about one-fifth of the fuselage radius, and it occurs for those in columns and plates of typical densities whose major dimensions are about 600 μm and 2 mm, respectively.

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W. D. King

Abstract

The equations of motion for an ice crystal moving around a body are simplified and used to obtain the preferred angular orientation of the crystals with respect to the body. It is shown that the calculated orientation angles are in good agreement with those measured by under-wing probes, and that the major cause of the preferential orientation of columns is the vortex generated at the tips of finite wings. It is also shown that a preferred orientation can be found in data obtained using fuselage-mounted probes, but there the agreement between the calculated and observed angles is not as good.

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W. D. King

Abstract

It is shown that the air flow around PMS canisters can be simulated using just two source and a sink. The flow field is easy to compute and more accurate than the sphere approximation which has been used by other workers.

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W. D. Neff
and
C. W. King

Abstract

We describe a sequence of tethersonde and solar measurements showing the effects of the pooling of cold air drainages in a basin located along the Colorado River below the Brush drainage. Results obtained during periods of weak ambient winds show that the basin fills over a period of several hours, then eventually overflows. The depth of the pool is such as to affect tributary drainages, such as that of Brush Creek, and to cause the accumulating drainage jets to become elevated as they flow down the larger drainage channels into the basin.

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W. D. King
and
D. E. Turvey

Abstract

A constant temperature probe for the measurement of solid water content of clouds is described. The probe is operated at a temperature of approximately 25°C, and is designed to collect and melt ice particles that impact in an open half-cylinder, the amount of power supplied to the probe being related to the solid water content through its dimensions, etc. Comparisons in a small wind tunnel with values derived from weighings of oil-coated slides suggest that the probe is accurate to about 50%, while data from two different aircraft indicate that it performs reliably under flight conditions.

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W. D. King
and
R. J. Handsworth

Abstract

It is shown that when liquid water contents are measured with the CSIRO hot-wire element, and cloud transmission measured in the UV with a simple optical system, then the two measurements can be combined to yield total droplet concentrations and average droplet size. Sizes and concentrations obtained from this technique are compared with those from an optical scattering probe, and reasonable agreement is found.

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