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HAIL FORMATION, VERTICAL CURRENTS, AND ICING OF AIRCRAFT

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  • 1 Observatorio de Cordoba, Cordoba, Argentina
  • | 2 Agrupacion de Estudiantes de Fisica, La Plata, Argentina
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Abstract

The theory that hail formation depends on strong ascending currents in clouds and the theory that it depends on tornadic action are critically examined. Aeronautic experience shows that neither theory is necessary.

The time and the speed of falling of growing hailstones are calculated for a standard atmosphere at rest. A hailstone falls the first 4 km in about 5 min. Hailstones are assumed to form from subcooled water droplets and ice or snow crystals. While the surface is wet, a transparent layer forms; when it dries, an opaque white layer appears.

A tentative description of the formation of large hailstones is given. An absolute humidity of 10 gm−3 would allow a stone falling from 8 km to 4 km through an atmosphere at rest to grow to a diameter of 5 cm. Ascending motion, turbulence, electrical phenomena, larger absoulte humidity, and greater cloud height should permit larger hailstones.

Icing of aircraft appears to follow the same pattern as hail formation

Abstract

The theory that hail formation depends on strong ascending currents in clouds and the theory that it depends on tornadic action are critically examined. Aeronautic experience shows that neither theory is necessary.

The time and the speed of falling of growing hailstones are calculated for a standard atmosphere at rest. A hailstone falls the first 4 km in about 5 min. Hailstones are assumed to form from subcooled water droplets and ice or snow crystals. While the surface is wet, a transparent layer forms; when it dries, an opaque white layer appears.

A tentative description of the formation of large hailstones is given. An absolute humidity of 10 gm−3 would allow a stone falling from 8 km to 4 km through an atmosphere at rest to grow to a diameter of 5 cm. Ascending motion, turbulence, electrical phenomena, larger absoulte humidity, and greater cloud height should permit larger hailstones.

Icing of aircraft appears to follow the same pattern as hail formation

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