The formation and precipitation mechanism of two ordered patterns of embedded convection in stratiform cloud

Although convection embedded in stratiform cloud is often disordered, it is ordered under certain weather conditions. In particular, there are two forms of ordered convection: embedded convection with a ladder-like pattern and that with a parallel pattern. However, there is little literature regarding these patterns. Because stratiform clouds with embedded convection are major objects for weather-modification studies, it is important to explore the formation/development and characteristic precipitation of embedded convection from the perspective of cloud and precipitation physics. In this paper, using observation data, we simulate a large-scale precipitation event in China for July 19–21, 2007, employing the mesoscale Weather Research and Forecasting (WRF) model (V2.2). The rainfall-related clouds are analyzed through simulation, with particular focus being given to the genesis of embedded convection, the precipitation and microphysical properties. The results show that the WRF model can simulate features of this kind of nephsystem, indicating a close relationship between convection genesis and the 500 hPa trough and low-level convergence line. In such a favorable weather situation, there are two ordered patterns of embedded convection in the nephsystem, one being a group of convection centers arranged at different altitudes in a ladder-like manner and the other being a group of convection centers with a parallel pattern. In the first case, rainfall also has a ladder feature, with precipitation being highest for the top convection and reducing to the base convection. This implies that the higher the convection develops, the more active the microphysics in warm- and cold-cloud processes is, leading to greater precipitation; i.e. rainfall in a ladder-like distribution. In the second case, rainfall decreases step by step from south to north, with the precipitation depending strongly on the cloud-water content therein. The two patterns of embedded convection and their precipitation features and microphysics are intensively studied from a new point of view.