摘要
2004年7月4-6日,在我国东北地区有一次大范围的降雨过程。作者分析了此次层状云降雨的观测资料,包括机载PMS资料、雷达资料以及地面雨强计资料等,并用包含详细微物理过程的一维层状云模式进行了数值模拟,用顾震潮的三层概念模型(把层状云垂直结构分为三层:第一层为冰晶层,第二层为过冷水层,第三层为暖水层)分析了云的结构及降水形成过程。结果表明,这个模型基本反映了降水性层状云的结构和降水产生的物理过程。在第一层中,冰晶的凝华增长很重要,也存在冰晶的碰并过程。在第二层中,冰晶和雪的增长主要是通过凝华过程,Bergeron过程作用很大,但不同时刻Bergeron过程的作用程度不同。第三层中主要有云滴、雨滴和从第二层降落下来以后融化的雪和霰。云的第一层对第二层有播种作用,冰晶层对降水的贡献为7%,过冷水层对降水的贡献为54%,暖水层对降水的贡献为39%,降水的产生中冷云过程作用稍大,但暖云过程也起重要作用。
The purpose of this paper is to analyze the structure of a stratiform cloud and physical processes of precipitation formation through the observational data of airborne particle measuring system （PMS）, Doppler radar and rainfall in situ on 5 July 2004 in Changchun, Jilin Province. A numerical simulation is also conducted using one dimensional, time-dependent stratiform cloud model with detailed microphysical processes. The synoptic analysis shows that this stratiform precipitation process is induced by the typhoon, Mindulle, when it evolves into a low-pressure system. On the radar echo image, there is an obvious bright band. The observational PMS data indicate that the average number concentration of ice crystal is 2. 6 × 10^4 m^-3 and the supercooled water content is abundant above the 0℃ level. Below the 0℃ level, the water content is smaller. A one-dimensional cloud model is employed.The simulated results are well consistent with the observations. Koo Chen-Chao＇s three-layer cloud conceptual model can interpret the structure of the stratiform cloud well. In the first layer, namely ice crystal layer, the main water substance is ice crystal. The growth of ice crystals by deposition is very important. Besides this, the ice crystals grow also by collision-aggregation process that induces some snow crystals. The key parameter of this layer is the temperature of cloud top. In the second layer, namely supercooled water layer, there are composed by ice crystal, snow, graupel, cloud droplet and raindrop. The ice crystals grow by diffusion of water vapor to their surface due to the Bergeron process. The snow crystals grow by deposition. The snow crystals and graupels grow by collision and aggregation, collection and riming with snow crystals, graupel particles, and ice crystals. In addition, the cloud droplets transform to raindrops through autoconversion. The key parameters of the second layer are the content and thickness of supercooled water. In the third layer, namely warm water layer, the main water substances are cloud droplet, raindrop, and melting snow and graupel. The 50%- 60% of raindrops below the melting level come from the melting snow crystals and graupel particles. The raindrops grow almost through gravitational collision. Therefore, the thickness and water content of the warm layer are the determinate factors.
The three layers, ice crystal layer, supercooled water layer and warm water layer, contribute 7%, 54% and 39% to the surface precipitation, respectively. The first layer seeds ice crystals and a little snow crystals to the feeder cloud （the second layer）. And the second layer seeds snow crystals, graupel particles and raindrops to the feeder cloud （the third layer）. The extent of Bergeron process is very different at different times and layers, and warm cloud process is crucial sometimes.
出处
《大气科学》
CSCD
北大核心
2007年第3期425-439,共15页
Chinese Journal of Atmospheric Sciences
基金
中国科学院创新项目KZCX3-SW-225
国家自然科学基金资助项目40333033
40475005
关键词
层状
云观测和数值模拟
三层模型
降水机制
stratiform cloud, observation and simulation, three-layer cloud conceptual model, precipitation mechanism
