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All methods and instruments currently being used for the physical characterization of hailstones are listed and discussed. Apart from the simpler measurements of diameter, shape, roughness, surface temperature, etc., particular attention is paid to the aerodynamic forces acting on free-falling hailstones and to the way these forces are ascertained. Further paragraphs are devoted to the technique for obtaining thin sections and to their importance in explaining the growth of ice particles. The application of calorimeters and separators in demonstrating the presence of liquid water in the hailstones is also discussed.
All these methods can be used for investigating artificially produced ice particles.
All methods and instruments currently being used for the physical characterization of hailstones are listed and discussed. Apart from the simpler measurements of diameter, shape, roughness, surface temperature, etc., particular attention is paid to the aerodynamic forces acting on free-falling hailstones and to the way these forces are ascertained. Further paragraphs are devoted to the technique for obtaining thin sections and to their importance in explaining the growth of ice particles. The application of calorimeters and separators in demonstrating the presence of liquid water in the hailstones is also discussed.
All these methods can be used for investigating artificially produced ice particles.
Abstract
Hollow spheres filled with ethylenedichloride and snowballs of low mechanical cohesion drenched in water were exposed to blast waves. They did not show any effect that could be attributed to the explosion of 1 kg TNT at distances of 5 m and more from the explosive charge. The same conclusion was indicated by similar experiments in which artificial hailstones consisting of ice-water mixtures, grown in a hail tunnel, were used as test objects.
Therefore no justification is given for attempting to combat hail by any mechanical softening of the hail-stones-in the immediate proximity of exploding rockets.
Abstract
Hollow spheres filled with ethylenedichloride and snowballs of low mechanical cohesion drenched in water were exposed to blast waves. They did not show any effect that could be attributed to the explosion of 1 kg TNT at distances of 5 m and more from the explosive charge. The same conclusion was indicated by similar experiments in which artificial hailstones consisting of ice-water mixtures, grown in a hail tunnel, were used as test objects.
Therefore no justification is given for attempting to combat hail by any mechanical softening of the hail-stones-in the immediate proximity of exploding rockets.
Abstract
By setting up and solving general equations for the heat balance and the material transfer between a spherical hailstone and its environment it is possible to show how the different variables such as air temperature, air pressure, liquid water content of the air (in the form of drops), hailstone diameter, speed of fall of the hailstone, its surface temperature and growth rate are interdependent. At the same time growth zones can he delimited within which accretion is accompanied by evaporation or sublimation of H20, or where an increase of mass by sublimation exceeds the amount of accretion. From the growth conditions it is possible to classify the resulting ice deposits on a physical basis.
Abstract
By setting up and solving general equations for the heat balance and the material transfer between a spherical hailstone and its environment it is possible to show how the different variables such as air temperature, air pressure, liquid water content of the air (in the form of drops), hailstone diameter, speed of fall of the hailstone, its surface temperature and growth rate are interdependent. At the same time growth zones can he delimited within which accretion is accompanied by evaporation or sublimation of H20, or where an increase of mass by sublimation exceeds the amount of accretion. From the growth conditions it is possible to classify the resulting ice deposits on a physical basis.
Abstract
Modeling by Gillesple and List established the evolution to equilibrium of raindrop number distributions in one-dimensional shaft models. Donaldson and List et al. (LDS) then demonstrated mathematically that equilibrium distributionsƒ for raindrop number concentration N consist of a product of the rainfall rate R and a shape function Δ (which is independent of Donaldson et al. and LDS) showed that such spectra contain three at diameters of ∼0.3, 0.8 and 1.8 mm, whereas Brown obtained only the two smaller ones.
For equilibrium distributions, the present shows that the mass concentration M and the radar reflectivity Z are also proportional to the rainfall rate R, with Z=C z R and that N,M, R and Z are mutually proportional. Calculation provided C z=742μm3 (mm h−1)−1, which is suggested to be a universal constant for steady tropical rain.
Data from a tropical rain experiment, carried out jointly by the Malaysian Meteorological Service and the University of Toronto, confirmed the equilibrium peaks at diameters of ∼0.3 (estimate), 0.9 and 1.9 mm. Due to basic deficiencies of the disdrometer only study state events could be used to assess radar reflectivities. The four available cases of steady rain consist of 112 one-minute spectra with different types and origins of MID (warm clouds, clouds containing ice particles, convective or stratiform clouds). As in the model, the radar reflectivity Z as calculated from measured drop spectra, was found to be proportional to rainfall rate.
Abstract
Modeling by Gillesple and List established the evolution to equilibrium of raindrop number distributions in one-dimensional shaft models. Donaldson and List et al. (LDS) then demonstrated mathematically that equilibrium distributionsƒ for raindrop number concentration N consist of a product of the rainfall rate R and a shape function Δ (which is independent of Donaldson et al. and LDS) showed that such spectra contain three at diameters of ∼0.3, 0.8 and 1.8 mm, whereas Brown obtained only the two smaller ones.
For equilibrium distributions, the present shows that the mass concentration M and the radar reflectivity Z are also proportional to the rainfall rate R, with Z=C z R and that N,M, R and Z are mutually proportional. Calculation provided C z=742μm3 (mm h−1)−1, which is suggested to be a universal constant for steady tropical rain.
Data from a tropical rain experiment, carried out jointly by the Malaysian Meteorological Service and the University of Toronto, confirmed the equilibrium peaks at diameters of ∼0.3 (estimate), 0.9 and 1.9 mm. Due to basic deficiencies of the disdrometer only study state events could be used to assess radar reflectivities. The four available cases of steady rain consist of 112 one-minute spectra with different types and origins of MID (warm clouds, clouds containing ice particles, convective or stratiform clouds). As in the model, the radar reflectivity Z as calculated from measured drop spectra, was found to be proportional to rainfall rate.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
In conformity with experimental results the heat transfer of gyrating spherical hailstones is divided into two parts. One takes place over a normally wet but supercooled equatorial region of limited roughness, whiles the other occurs over a rough, dry polar zone which is at a substantially lower temperature than the equatorial region. The sensitivity of this complex heat transfer is studied by establishing the response of the heat transfer to changes of 15 individual parameters relative to the results of a single hailstone growth experiment.
The propagation of errors in individually setting the icing conditions of a laboratory experiment is somewhat different from the sensitivity study. Both sensitivity and error hierarchies are given and conclusions are made about measurement accuracies. The measurements for the case at hand suggest that treating hailstones as smooth, nonrotating particles underestimates the heat transfer by a factor as high as two. For the treatment of a whole dataset containing many hailstone growth experiments, roughness may no longer be considered as a single-valued quantity since it seems to vary with hailstone latitude and icing conditions.
The tool used, the “spreadsheet,” is ideal to assess the complex heat budget. It serves to indicate potential problems before large experimental series are launched.
Abstract
In conformity with experimental results the heat transfer of gyrating spherical hailstones is divided into two parts. One takes place over a normally wet but supercooled equatorial region of limited roughness, whiles the other occurs over a rough, dry polar zone which is at a substantially lower temperature than the equatorial region. The sensitivity of this complex heat transfer is studied by establishing the response of the heat transfer to changes of 15 individual parameters relative to the results of a single hailstone growth experiment.
The propagation of errors in individually setting the icing conditions of a laboratory experiment is somewhat different from the sensitivity study. Both sensitivity and error hierarchies are given and conclusions are made about measurement accuracies. The measurements for the case at hand suggest that treating hailstones as smooth, nonrotating particles underestimates the heat transfer by a factor as high as two. For the treatment of a whole dataset containing many hailstone growth experiments, roughness may no longer be considered as a single-valued quantity since it seems to vary with hailstone latitude and icing conditions.
The tool used, the “spreadsheet,” is ideal to assess the complex heat budget. It serves to indicate potential problems before large experimental series are launched.
