Microphysical parameters in relation to tropical cloud and precipitation distributions and their modification

Abstract

Microphysical parameters and the vertical wind profile are considered in relation to the shapes of spatial and temporal distributions of tropical rainfall. For a particular vertical velocity field, the precipitation beneath an updraft center is concentrated relative to that away from the center by increasing relative numbers of small drops in the distribution of rain particles. Increased collection efficiency of rain for cloud and a faster rate of growth of cloud particles reduces the amount of condensate which is carried to high levels and lost by effects of horizontal divergence to the immediate precipitation at the ground. The time of precipitation onset at the ground is related to updraft speed, drop distribution parameters, collection efficiencies, and cloud conversion rates. Relatively large changes of the microphysical parameters are required to alter the rain distribution at the ground appreciably, because the responses of water distribution in the model system usually tend to offset the effects of the microphysical changes. Possible responses of cloudiness and precipitation to modification of the microphysical parameters are discussed in the light of the model, with the assumption that the updraft distribution is unaffected by variations of the vertical profiles of cloud and precipitation. The possible of the Earth is also noted.