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T. Ohtake

Abstract

Size distributions of snowflakes and raindrops were obtained simultaneously at two altitudes along mountain slopes. The snow size distributions generally agreed with the Gunn and Marshall snowflake distribution, but were sometimes similar to the Marshall and Palmer raindrop distribution. Raindrops sampled just below the melting layer tended to have the same pattern of size distributions as snowflakes appearing at the upper station above the melting layer. The times at which the modes of distribution changed were the same at both stations. The implication is that most of the snowflakes do not break up into several small raindrops during melting.

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T. Kobayashi and T. Ohtake

Abstract

Many prismatic ice crystals have been observed to have grooves which circle the prism faces at right angles to the c-axis. In both natural and artificial crystals the grooves appear when the crystal is evaporating and disappear when it is growing. A possible ice-twinning structure is proposed to explain these observations, analogous to zinc-blende rotation twins and implying a diamond-structured layer at the interface.

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K. O. L. F. Jayaweera and T. Ohtake

Abstract

Single unrimed columnar ice crystals (>200 µm in length) from shallow layer clouds were collected in silicone oil, photographed under a microscope, and melted to determine their mass. These ice crystals were representative of those growing in a water sub-saturated environment in the temperature range −4 to −10C. The axial lengths of the crystals were related by the expression D = 6.3 L 0.437, where D and L are the lengths of the minor and major axes, expressed in micrometers, and have a nearly constant density of 0.3 gm cm−3. The habit of the ice crystals was very similar to those obtained in the water-droplet-free environment of laboratory diffusion chambers and was elementary or bundles of sheaths. Present observations suggest that bundles originate by the growth of secondary ice crystals on the prism face of the crystal. These secondary ice crystals then grow on the surface of the parent crystal and may grow at a rate faster than, and at the expense of, the parent crystal. The results of these observations were compared with those made on ice crystals growing in clouds supersaturated with respect to water.

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T. E. Osterkamp, T. Ohtake, and D. C. Warniment

Abstract

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