| Summary: | 碩士 === 國立臺灣大學 === 大氣科學研究所 === 96 === Humans cannot live without water. Due to the influence of increasing populations and degree of industrialization on global climate and environment, human influence on precipitation efficiency became a very important issue. Precipitation is one of the most basic commodities on earth sustaining human life. Its efficiency is strongly influence by aerosol particles that serve as cloud condensation nuclei (CCN) and ice nuclei (IN).
Some past studies indicated that more aerosols may result in more but smaller cloud drops. Smaller cloud drops would suppresses drop coalescence thus inhibit precipitation formation. But there are also studies that shown otherwise. The aerosol effect on clouds remains an unsolved issue and the processes involved are complicated and nonlinear.
The main motivation of this study is to gain a better understanding of the mechanisms involved in this aerosol-cloud interaction, using a non-hydrostatic mesoscale cloud model (MM5) as the main tool. A C&L Reisner 2 scheme that considers the effects of CCN on precipitation is incorporated into this model. The simulation results indicated that different concentration of aerosols has different effect on precipitation depending on the types of cloud system. More aerosols generally produce more and smaller cloud drops and inhibit warm rain formation; it also enhances the deposition growth of ice particles but limits their growth by riming. In the deep convective cloud system that simulated here, increasing aerosol can enhance surface rainfall; but for the shallow convective cloud system the surface precipitation is reduced. Increasing IN not necessary increase or decrease precipitation, and the effect actually depends on the strength of homogeneous nucleation and other nucleation processes. Overall, aerosols play complicated and nonlinear roles in precipitation process.
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