Characteristics of Raindrop Size Distribution Dependent on the Life Stage of a Convective Precipitation Cloud in the Baiu Season

A convective cloud varies considerably in physical structure from development to dissipation. This variation results in changes in the Raindrop Size Distribution (RSD) in the precipitation from a convective cloud. The characteristics of RSD in the life stages of a convective cloud are compared, based on the data measured by an optical raindrop spectrometer during the field projects; TREX (1996), X-BAIU-98 (1998), and X-BAIU-99 (1999), performed on the southern and western coasts of Kyushu Island in the Baiu season. The convective clouds that passed over the observational site were classified as being in the mature, or the dissipation stage. The relationship between the shape of the RSD, and the convective activity of the convective clouds, varied according to the stage of development. When clouds are in the mature stage, the raindrop number concentration in every size range increases as the convective activity increases. On the other hand, when clouds are in the dissipation stage, the raindrop number concentration with larger sizes tends to increase as the convective activity in the mature stage increases. On the basis of these new findings obtained from observations, the major precipitation mechanism is expected to change in the life stages of convective cloud.