Some Aspects of Rain Formation in Warm Cloud (II). Liquid Water Content as a Function of Upward Velocity

[摘要] The liquid water content of a precipitating warm cloud is expressed as a function of upward velocity, taking into account the difference between the rate of condensation which accumulates the liquid water in the cloud and the rate of rainfall, which carries it out of the cloud. As for the condensation nuclei of raindrops, a simplified analytical expression of woodcock's size distribution (1953) is used.The liquid water content in a steady state is found to be proportional to 1/3 power of the upward velocity, the numerical values of which, for example, are 0.42, 0.90 and 1.93g/m3 for upward velocities 10cm/sec, 1 and 10m/sec respectively in a typical condition for the cloud and sea-salt nuclei.In transient state, the liquid water content of the cloud is found to take a maximum at a certain time after the beginning of cloud formation if upward velocities are larger than 10cm/sec, thereafter it begins to decrease due to falling out of raindrops and approaches a value of steady state.Preferred appropriate upward velocity for initial raindrop formation due to the presence of large sea-salt nuclei is discriminated from that due to the coalescence mechanism under the presence of various size distribution of nuclei.Effect of the entrainment of surrounding air into cloud on the salinity of rain water is qualitatively discussed from the viewpoint of nuclei budget of the cloud.

[学科分类] 大气科学