摘要
边界层是中尺度对流系统(MCS)动力和水汽的主要来源。针对东北冷涡中MCS的边界层特征及边界层对MCS的触发和维持机理,应用MM5模式耦合Noar陆面模式对2004年7月5日发生在辽宁中西部的强对流过程进行了数值模拟。重点分析了MCS不同发展阶段边界层三维气流结构、边界层冷丘、边界层层结结构及其在MCS触发和维持中的影响。结果表明,本次MCS在边界层有3股明显的气流汇合于雷暴区,1股是来源于东北部长白山稳定气团的东北气流,1股是西北部的西北下沉气流,1股是西南气流,浅薄的东北部底层冷空气有利于西南气流的上升,形成对流。MCS初期边界层低层的辐合强于边界层高层辐合,边界层气流旋转作用较弱,边界层辐合线是对流触发的重要因素之一。MCS边界层上层的中尺度辐合涡旋主要由环境场辐合,边界层摩擦抽吸形成,是对流重要的能量、水汽输送系统,它伴随着强对流的发展而出现,同时对对流的维持、发展有重要的反馈作用,是边界层与自由大气进行交换的重要系统,是对流系统维持的入流的主要入口。MCS边界层冷丘内部为潜在稳定层结,特别在近地面层形成了非常稳定的层结,其温湿层结及气流结构改变了边界层入流。
Boundary layer is the major source of motivity and vapor for meso-scale convective systems（ MCS）. A severe storm event in the mid-west of Liaoning province on 5 July 2004 was simulated using the MM5（V3.6） coupled with the Noar LSM, to explore the boundary layer characteristics, and the triggering and maintaining mechanism of a MCS in the cold vortex process over Northeast China. The 3-D airflow structure, cold air dome, stratification structure of the boundary layer and their effects on the triggering and maintaining of the MCS were emphatically analyzed. The conclusions are as follow： there were 3 airflows converging in the area of the MCS; the first was the northeast flow from a stable air mass over the Changbai Mountains, the second was the northwest sinking flow from northwest Liaoning province and the third was a southwest flow. The shallow cold air in the bottom of the boundary layer in the northeast was favorable to the rise of the southwest flow and the generation of convection. In the initial stage, the convergence of the low layer was stronger than that of the upper layer of the boundary layer, and the rotation of the boundary layer flow was weak, so a convergence line of the boundary layer was one of important factors to trigger convection. In accompany with development of strong convection, a mesoscale vortex formed within the MCS at the upper boundary layer driven by convergence of the environmental wind field and Ekman pumping; it on one hand was the major entry for the inflow of the MCS, and on the other hand provided an important feedback to the maintain and development of convection. The cold air dome resulted from precipitation evaporation led to the formation of the stable stratification in the near surface layer, and the evolution of its temperature and moist stratifications and flow structure changed the inflow of the MCS from the boundary layer.
出处
《气象学报》
CAS
CSCD
北大核心
2009年第1期75-82,共8页
Acta Meteorologica Sinica
基金
国家自然科学基金(40375020)
关键词
MCS
边界层
温湿结构
冷丘
Mesoscale convective system, Boundary layer, Temperature and moisture structure, Cold air dome
