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The responses of cloud physical processes of a developing tropical deep convection to the increase of CCN concentration have been studied using a three‐dimensional cloud‐resolving model. Three sets of model simulations, each consisting of 30 runs initialized using a set of 30 different CCN profiles with maximum concentrations ranging from 50 to 6000/cm 3 , have been carried out. The finding of this study that cloud droplet number concentration increases while cloud droplet size decreases with aerosol concentration is similar to the previous results mainly revealed in studies of stratiform clouds. However, the responses to increasing aerosol concentration of many other cloud properties illustrated in this study, particularly precipitation, are very different from those found or suggested in studies of stratiform clouds. Increasing CCN concentration causes a stronger convection, added mass of condensed water, and enhanced microphysical conversions, all leading to the increase in precipitation as well as the expansion of the cloud coverage. Interestingly, when initial CCN concentration exceeds a certain level, many of the above effects become insignificant, suggesting a relationship between some cloud properties and the logarithm of CCN concentration and further implying that a more substantial aerosol effect on deep convection could be seen over a clean rather than polluted region. Overall speaking, increasing CCN concentration does not significantly affect the precipitation efficiency. The increase with CCN concentration of upward flux of water vapor entering the cloud thus leads to an enhancement in moistening the free troposphere brought by the modeled cloud, besides adding more precipitation to the ground.
Chien Wang (Tue,) studied this question.