1.Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration,and Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters,Nanjing University of Information Science Technology;2.Institute of Urban Meteorology,Chinese Meteorological Administration,Beijing
云滴谱离散度是云雨自动转化过程参数化中不可忽视的重要参数,对地面降水有着重要的影响。本文利用WRF-Chem (The Weather Research and Forecast coupled with Chemistry) 模式,对发生在2019年1月3日至6日长江中下游地区的一次降水过程进行了模拟。在清洁和污染的气溶胶背景下,设定不同的云滴谱离散度的数值(0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0),研究云降水微物理的变化。结果表明,该个例的降水主要来源于云雨自动转化以及云雨碰并过程。在清洁条件下的地面累计降水量大于在污染条件下的累计降水量,这是因为在清洁条件下云滴数浓度小,有利于云雨自动转化以及云雨碰并过程。虽然云雨自动转化以及云雨碰并过程占主导,但导致地面累计降水量随云滴谱离散度增大而增大的主要原因是：随着云滴谱离散度的增大,冰粒子质量浓度增大,导致融化过程增强,产生更多的雨滴,从而增强地表降水。所得结果将提高云降水对气溶胶和离散度响应过程的理论认识。
The dispersion of cloud droplet spectral dispersion is an important parameter that cannot be ignored in the parameterization of autoconversion, and has an important influence on surface precipitation. In this study, the weather research and forecast coupled with chemistry (WRF-Chem) model was used to simulate a precipitation process in the middle and lower reaches of the Yangtze River from January 3, 2019, to January 6, 2019. Different values of cloud droplet spectral dispersion (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were set to study the microphysical changes of cloud and precipitation under the clean and polluted backgrounds. The results show that the precipitation in this case mainly comes from the autoconversion from cloud droplets to rain and the accretion of cloud droplets by rain. The accumulated precipitation under the clean condition is greater than that under the polluted condition because the concentration of cloud droplets is smaller under the clean condition, which is beneficial to autoconversion and accretion. Although the autoconversion and accretion are dominant during precipitation processes, the main reasons leading to the increase of accumulated precipitation with the increase of cloud droplet spectral dispersion are as follows: With the increase of cloud droplet spectral dispersion, the mass concentration of ice particles increases, which leads to the enhancement of melting process and more raindrops, thus enhancing surface precipitation. The results will improve the theoretical understanding of the response of cloud and precipitation process to aerosol and cloud droplet spectral dispersion.