对流云中冰相过程的三维数值模拟——Ⅱ:繁生过程作用

Three-Dimensional Numerical Simulation of Ice Phase Microphysics in Cumulus Clouds. Part II: Effects of Multiplication Processes

在可压缩三维冷云数值模式里对冰晶繁生过程进行了参数化,显式考虑了过冷滴冻结破裂和Hallett-Mossop两个繁生机制,并对冰晶浓度进行了订正。对暖底孤立积云的模拟实例表明繁生作用对对流系统宏观特征没有显著改变,地面总降水略有增加,最大雨强增大且时间提前。繁生过程的主要作用是改变了云的微物理结构特征,使云中冰化时间提早,冰化程度大大加强,引起云上部增暖并抬高云顶。在所考虑的两个繁生机制中,冻结破裂繁生机制是引起微物理结构发生变化的主要过程。还对各冰相微物理过程的相对作用进行了分析。

Two ice crystal multiplication processes are parameterized in the compressible three-dimensional numerical cloud model described in part I of this study. The formation of secondary ice crystals by shattering of relatively large supercooled drops during freezing and Hallett-Mossop mechanism are explicitly considered, and the ice crystal concentration is modified . For isolated convective clouds with warm bases; the simulations show that the inclusion of ice multiplication processes causes insignificant modification on the cloud dynamics and macro-features , the simulated cloud only produces slightly more total ground precipitation whereas the maximum precipitation rate is increased and the appearing time of ice crystals is earlier. However, the processes do affect the microphysics of the cloud : They promote ice glaciation in clouds. As a result, more latent heat released warms the upper portion of the cloud and causes a higher cloud top. In the two multiplication processes, the shattering mechanism plays a dominant role in affecting on the cloud microphysics. The relative importance of each ice phase process is also analyzed .