Abstract
Three-dimensional distributions of precipitation water in a maritime cumulus cloud are investigated in detail through the life time by analyzing digital data of radar echo which were obtained at Miyako Island in the East China Sea during AMTEX'75. A preliminary consideration on the budget of precipitation water in the early period of the mature stage is also presented under a hypothetical assumption of vertical velocity. The macroscopic feature of the radar echo observed is that the maximum radar reflectivity is 42dB, the maximum height 4.9km and the life time 44min or so. The main results obtained in this study are as follows. (1) Although the cloud has a fairly long "nursing stage", the evolution is very rapid as soon as it begins to develop. The maximum ascent rate of the top of the radar echo is about 9m/s. (2) The larger value of radar reflectivity is analyzed around the central portion of the radar echo, which is located at 3 to 4km level during the mature stage. This suggests the existence of the localized accumulation zone of higher precipitation water. (3) In the early period of the mature stage, the radar echo shows little inclination together with little change of horizontal dimension in the vertical in spite of the existence of noticeable vertical wind shear. (4) The averaged horizontal size of the major portion of the radar echo is about 4 times in the early period of the mature stage and the most extensive region through the life time, which appears at a fairly low level (1.5 to 2km) in the decaying stage, is about 7.5 times as large as that just before development. (5) The movement of the radar echo is governed by the wind at extremely low level (about 1km) during the mature stage and it moves to the left of the wind in the middle layer. (6) According to a preliminary consideration on the budget of precipitation water, the generation of precipitation water is prominent in the middle layer of the cloud to result in its net increase against the loss due to mixing with the environmental air together with vertical advection. On the other hand, the increase due to vertical advection in the upper layer is almost canceled by evaporation, relative sedimentation and turbulent mixing, while in the layer around the cloud base evaporation is noticeable.
We compared our results with some of the works by other researchers.
