| Urban is the most concentrated region of human activities. The urbanization may induce the distinct change of atmospheric environment, such as changes of atmospheric composition, land use and boundary structure etc. Whether these changes can induce the alteration of regional water cycle is a hot research topic. Since atmospheric precipitation is a main source of fresh water on and under the ground, the recharge of the water storage will be not enough in case of the decrease of atmospheric precipitation, which will produce a series of regional problems of ecosystem, environment as well as geology such as desertification, land-surface sink etc.China is undergoing a rapid urbanization stage, and the shortage of fresh water is becoming a serious problem with the rapid expanding of urban number and scale. Over 400 cities are suffering the water shortage, and 110 cities are under serious water shortage in 669 cities, in which cities like Beijing, Tianjin, Qingdao, Dalian etc are the most. The decrease of underground water level has already induced a series of geological and environmental problems due to the excessive use of underground water, which has brought wide public concern.Although many researches in the effect of urbanization on precipitation have been conducted in the past several decades, the conclusions are not consistent. One of important reasons of this is due to that the different city is located in different geographic and climatic background such as coastal, topographic and different climatic regions, the alteration of cloud and precipitation induced by urbanization is quite different.The research of urban effect in China has mainly focused on urban heat island and environmental problems, and that in the effect of urbanization on precipitation and regional water cycle is few. The prominent feature of urbanization in China is the heavy pollution emissions. Therefore, the research of this dissertation will focus on the clarification of the effect mechanism of polluted atmospheric aerosols as cloud condensation nuclei (CCN) on cloud and precipitation based on aircraft measurement and numerical simulation studies. The cloud and aerosol interaction is also an important aspect in climate change, and this research can also provide reference in the exploitation and use of atmospheric water source.The structure and aerosol-cloud interaction for a typical precipitating convection embedded stratiform clouds was investigated based on the aircraft measurement data collected during the Comprehensive Observation Period of National key Sci.& Tech. Project in the Beijing surrounding regions, and then the effect of size and concentration of aerosol on cloud and precipitation under the polluted atmospheric environment was conducted based a parcel model and a mesocale cloud-resolving model.The aircraft measurement indicated that the convective cells embedded in stratiform clouds are the most active regions for aerosol-cloud interactions. The results showed that the quite different features in cells indicate that the formation mechanism from aerosol to cloud dropelet is different. Small-size aerosol forms cloud droplet primarily by cloud condensation nucleation process, and that larger-size aerosol may form cloud droplets by both condensation and coalescence preocesses.Based on the observation, numerical experiments were conducted to investigate precipitation enhancement of convective clouds contaminated with ammonium sulfate particles by seeding of potassium chloride particles in the urbanized region of northern China. Modeling studies show that the size and concentration of potassium chloride particles plays a critical role in the precipitation enhancement of the polluted clouds. The cloud adding with particles sizes less than 0.1μm in diameter have little influence on the precipitation formation while those from 0.1μm to 1μm in diameter can generate the largest total number concentration of cloud droplets, smallest size of cloud droplets and longest cloud lifetime, and lead to a delayed precipitation formation. The cloud adding with particles sizing from 1μm to 2.5μm in diameter can produce the most amount of drizzles while those sizing from 2.5μm to 10μm in diameter can have the largest effects on cloud lifetime and precipitation development. The different concentrations of large size aerosols had different effects. With the increasing of concentration, it can accelerate the formation of raindrop, but the change could slow down when the concentrations were very high. With different concentrations, the large size aerosols all inhibited the drizzle formation and unchanged the appearance time of raindrop. The aircraft measurements conducted in the convective cells embedded in stratiform clouds in the study region provides strong supports for the model-derived results.WRF model was used to study the effects of aerosol on cloud and precipitation formation in real meteorology condition. The results were compared to the observation. The effects of different initial CCN concentration on cloud formation were further tested. The initial CCN concentrations were input based on the clean condition, model initial value and aircraft observations. The result shows that with the increase of initial CCN concentration, the cloud droplet concentration was also increased, and the rain drop concentration was decreased, especially in the heavy polluted condition. The simulated precipitation was decreased by the effect of high aerosol concentration. It suggests that the aerosols did produce a stronge impact on cloud and precipitation.
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