一次强降水过程涡旋状MCS结构特征及成因初步分析

Preliminary Analysis of Structure Characteristics and Causes for Heavy-Rain-Producing Vortex-Shaped MCS

利用新一代天气雷达资料分析了造成2011年6月18日湖北省江汉平原强降水涡旋状中尺度对流系统(MCS)发生发展过程的结构特征,联合常规观测、地面加密观测及雷达四维变分风场反演资料初步研究了MCS可能成因。结果表明:(1)成熟阶段的强降水涡旋状MCS回波表现为气旋性弯曲的多条螺旋对流回波带、周围被大片层状云回波所包裹的结构特征,后期因冷空气侵入演变出冷暖锋式结构。回波合并和旋转式列车效应是产生强降水的主要运动特征。(2)涡旋状MCS是在有利环境场下,主要由鄂西山地一江汉平原过渡带边界层中尺度涡旋系统强烈发展组织的结果。(3)中尺度涡旋系统形成发展与地面暖倒槽发展、西南低涡前侧降水和特殊地形作用有密切关系,来自不同方向气流形成的强烈辐合是其前期形成发展的主要机制,后期发展可能与潜热释放有关,涡旋环流向上发展到700 hPa。

Radar echo characteristics of the vortex-shaped mesoscale convective system （MCS） that pro- duced heavy rain in Jianghan Plain of Hubei Province on 18 June 2011 and the possible causes of MCS structure are analyzed by using Doppler radar data, conventional observations and dense surface observa- tions and the radar 4D-Var wind retrieval data. The results show that： （1） Heavy-rain-producing vortex- shaped MCS echoes in mature stage showed multiple spiral convective echo belts with cyclonic curvature, surrounded by stratiform cloud echoes and evolving into the cold and warm frontal structure as a result of invasion of cold air. Echo merger and vorticity train effect are the main characteristics of motion in produ- cing severe precipitation. （2） The vortex-shaped MCS which was in favorable environment was the result of severe development of boundary layer mesoscale vortex system in the transition zone of western Hubei mountain and Jianghan Plain. （3） The formation of the mesoscale vortex system was closely related to the development of the surface reverted warm trough, rainfall in the front of the southwest vortex and special terrain. Strong convergence of airflows from different directions was the main mechanism of the develop- ment in its earlier stage. The late development might be related to latent heat release, for the vortex circu- lation developed upward to 700 hPa.