Abstract
The properties of diamond dust type ice crystals were studied from replicas obtained during the 1975 austral summer at South Pole Station, Antarctica. The time variation of the number concentration and shapes of crystals, and the length of the c-axis, the axial ratio (c/a) and the growth mode of columnar type crystal were examined at an air temperature of -35°C.
Columnar type crystals prevailed, but occasionally more than half the number of ice crystals were plate types, including hexagonal, scalene hexagonal, pentagonal, rhombic, trapezoidal and triangular plates. A time variation of two hour periodicity was found in the number concentration of columnar and plate type crystals. When the number concentration of columnar type crystals decreased, the length of the c-axis of columnar type crystals also decreased. When the number concentration of columnar type crystals increased, the length of the c-axis of the crystals also increased. There was sufficient water vapor to grow these ice crystals in a supersaturation layer several tens to several hundred meters above the surface.
The growth mode of columnar type crystals was different from that of warm and cold region columns reported by Ono (1969). The mass growth rate was 6.0×10-10gr•sec-1, and was similar to that obtained in cold room experiments by Mason (1953), but less than that found in field experiments by Isono, et al. (1956).
The plate type crystals prevailed occasionally at an air temperature of -35°C, at which the sheath, hollow and solid prism (column) usually prevail. An important question arises with respect to the crystal habit with air temperature lower than -22°C in the Ta-Δρ diagram consolidated by Kobayashi (1961).
