云并合的初始位置探讨

Initial Part Discussion of Cloud Merger

尽管很多云的并合过程最初是从云的中下部开始的（在这方面开展了大量研究）,但我们在观测中发现也有相当数量的云并合过程最初是从云的中上部开始的（然而这方面的文献记载很少）。基于云并合对云降水过程演变的重要作用,本文从个例研究入手,利用中尺度数值模式WRF,模拟2005年5月17～18日发生在我国西南山区（主要以贵州省为主）的一次云并合过程。在整个云（系）的发展过程中,前后共经历了数十次并合。观测和模拟结果表明并合共经历了三个阶段：（1）对流云单体间并合形成较大的对流云;（2）对流云并合形成对流云团;（3）对流云团并合形成范围较大的降水云系。在此次个例中：第一和第二阶段的并合首先是从云的中下部开始的,往往是处于发展阶段的云发生并合;第三阶段的云并合却是从云的中上部开始的,往往是那些比较成熟的对流云团发生并合。两种并合机制截然不同,但都与风切变和云内的上升气流速度密切相关。本文系统阐述了两种不同的并合机制。

Though many cloud merging processes begin from the middle and lower parts of clouds, but the authors find that many merging processes begin from the middle and upper parts of clouds. Because of the important effect of cloud merger, the authors studied a merging process on 17 May 2005 using a cloud-resolving mesoscale model WRF （Weather Research and Forecasting Model）. In this process, many mergers happened. Observation and simulation results show the process goes through three stages： （1） convective cells merging into a convective cloud; （2）convective clouds merging into a convective cloud cluster; （3） cloud clusters merging into a cloud system. The first and second stages of the merger process begin from the middle and lower parts, often between the young or developing clouds. The third stage of merger begins from the middle and upper parts, often between the mature cloud clusters. These two kinds of merging mechanisms are quite different, but both are related to wind shear and updraft velocity. In this paper, the authors set forth these two kinds of mechanisms in detail.