珠三角地区短期天气过程中大气气溶胶对云和降水的影响

The rapid economic development and the associated urbanization in the past thirty years have put tremendous stresses on the environment. The haze weather increases. Aerosols are fine particulates floating in the air and act as nuclei (CCN or IN) for the formation of cloud particles, thus affect the rainfall amount or frequency. The climate effect is one of the major uncertainties in the Intergovernmental Panel on Climate Change (IPCC) projection for global warming scenarios. .This study will examine the emission sources, transformation and distribution of aerosols in the Pearl River Delta region, and examine the detail short-term processes of aerosol, cloud and rainfall interactions using the most advanced weather forecasting model, coupled to aerosol chemistry, cloud microphysics and rainfall processes and calibrated and validated using ground and satellite observations. We will perform sensitivity tests to quantify some of the processes involved, such as evolution of cloud and rain drop concentration, cloud to rain conversion rate, and rate of aerosol removal by rainfall, and provide better parameterization to global climate models..An understanding of the sources and transport mechanism of regional aerosols is important for better city planning, design, environmental monitoring and knowledge of the interaction between aerosol, cloud and precipitation processes will enable quantification of aerosol impact on the rainfall type and frequency, thus contributing to development of environmental policies that are crucial to sustainable growth and development,and enhance the accurance of the forecast of air quality and short-term weather. Results from fine resolution models will enable improved parameterization of sub-grid processes in coarse scale global climate model for global warming scenario studies in the coming Intergovernmental Panel on Climate Change (IPCC) assessment.

三十年来珠江三角洲工业化和城市化进程非常迅速，灰霾天气增多。其中气溶胶可作为凝结核或冰核影响云和降水过程，因此气溶胶将对该地区空气质量、天气和气候产生重要影响。而气溶胶对云和降水的影响机制仍有很大的不确定性，是气候变化评估中最不确定的因子之一。本项目将通过地面观测和卫星遥感资料的分析，并采用一个包括气溶胶与云微物理以及大气化学过程的中尺度模式来进行华南地区短期天气过程的数值模拟和敏感性试验，试图定量化计算该地区气溶胶对云的结构和演变、云寿命、气溶胶的清除，对云和降水过程时空变化和分布，台风的路径、强度、降水、垂直结构，以及云微物理转化率等的影响，系统地研究珠江三角洲地区气溶胶与云和降水的相互作用及其综合影响。本项目可为提高空气质量和短期天气过程的预报准确率，和为全球环流模式的参数化提供更好的依据，不仅具有重要的科学意义，而且对提高珠江三角洲地区的天气和气候预测能力具有潜在的实际应用价值。

项目采用WRF-Chem模式围绕大气气溶胶对台风“天兔”的影响，对台风“珍珠”的影响，对一次大暴雨的影响等等进行了数值模拟研究。数值模拟表明，大气气溶胶对台风的路经和强度的不大，但是对台风的降水，水成物的分布以及云微物理过程有明显的影响。对台风和暴雨影响的数值模拟结果表明，气溶胶主要是通过间接效应而不是直接效应来影响台风和暴雨的。加入污染物排放源后，总累积降水量减少，而平均降水率峰值有所提高，并且降水初始时刻会比无污染物排放源时滞后一些。详细分析后可知，云水蒸发和雨水蒸发在降水初始阶段的减少，延缓了降水的发生；云水自动转化成雨水的增加致使雨水混合比在降水加强时段增加，造成平均降水率峰值的提高；以雨水被霰收集为主的冷云过程的减少导致总累积降水量减少。通过对比分析有无污染物排放源两种背景对云微物理转换过程随时间和空间变化的影响，以及直接效应和间接效应的模拟比较，进而了解云降水形成和发展的物理本质，进一步提高对珠三角地区气溶胶与云、降水之间的相互影响机理的认识。