Fukuta/Abstract Cirrus clouds often consist of polycrystalline ices, bullet- rosette in particular, and play an important role in the earth's radiative balance. Using a wedge-shaped ice thermal chamber and a continuous flow, horizontal gradient, ice-thermal diffusion chamber, the supersaturation temperature-polycrystalinity of formed ice crystals relationship and the growth of the polycrystalline ice will be studied with natural aerosol particles and pure water for the temperature down to about negative 38.5 degrees Celsius. Cirrus crystals frequently form out of supercooled clouds, and the vapor pressure of supercooled water is an important indicator for the phase equilbria and the phase change kinetics. Yet, the presently available data are extrapolated from those at higher temperature. Using the wedge-shaped ice thermal diffusion chamber with pure water droplets either free floating or supported on a nylon thread in the middle along the isothermal plane, and examining and comparing their growth/evaporation behaviour with the computed value, the vapor pressure of supercooled water will be determined for temperatures down to about negative 38.5 degrees Celsius and compared with the present table values.
