PRECIPITATION MECHANISMS OF CUMULONIMBUS CLOUDS AT POHNPEI, MICRONESIA

Eight specially developed radiosondes were sent into cumulonimbus clouds developed over Pohnpei, Micronesia. The radiosondes transmitted both the images and the electric charge of precipitation particles during their ascent through the clouds. Micronesian clouds contained numerous ice crystals. Interesting images of precipitation particles included spheroidal raindrops, frisbee-like snowflakes, tetrapod-like hailstones, and spatial crystals with wide planes near the tropopause. Precipitation mechanisms were identified through analysis of the precipitation particle distribution with regard to height. Three different cloud types were identified. Rainbands producing heavy precipitation grew frozen-particle-hailstones in a narrow layer just above the freezing level. Water accumulated heavily in this layer due to the interaction between the warm rain process and the drop freezing process. Two other cloud types seen were isolated cumulonimbus clouds and upper convective clouds. In the former, both warm rain and graupel formation processes worked independently, while graupel formation dominated in the latter cloud. Electric properties of clouds were also briefly described.