春季两次东移型西南涡云系的发展演变特征

Evolution Characteristics of Two Southwest Vortex Clouds Moving Eastward in Spring

采用FY-2E和Cloud Sat卫星资料、雷达资料、NCEP再分析资料和常规观测资料,分析2013年春季2次西南涡云型、云系结构和雷达回波演变、环境场特征。结果表明:(1)2次西南涡形成都伴随有高原槽东移和高原东侧偏南低空急流增强,偏南低空急流增强对低涡形成和东移起重要作用;(2)西南涡云系结构与低涡环流密切相关,西南涡形成和东移初期,低涡环流结构呈椭圆形,西南涡云系表现为叶状云系或逗点云系,随着低涡后部冷空气入侵加剧,低涡云系形成典型的"S"型后边界。低涡云系的结构形式和边界形状,对低涡形成和东移、急流发展有指示作用;(3)低涡降水分布与低涡云系结构有一定关系,低涡水平云系分布为叶状云系时,降水中心位于其东南部,低涡云系水平分布为逗点云系时,降水中心位于其逗点云内;(4)受低涡云系结构影响,低涡云系降水可分为2个阶段,第1阶段为低涡暖区降水,回波带呈反气旋弯曲,向东移动并向东北方向旋转;第2阶段中层干冷空气下沉加剧,干冷和暖湿气团交汇形成西南—东北向带状回波,雷达回波上"人"字形回波形成。

Based on FY-2E satellite and Cloud Sat cloud images,Doppler radar data,NCEP reanalysis data and the conventional observations,the evolution of the two southwest vortex clouds structures and radar echo as well as the favorable environmental field were analyzed. The results are as follows：（ 1） The formation of the southwest vortex was accompanied by the plateau trough moving eastward and the enhancing southwest jet over the eastside of the plateau. The cold and warm advection had an important role on formation and maintenance of the vortex.（ 2） The structure of the southwest vortex cloud was related closely with low vortex circulation,at the early stage of formation and moving eastward of the southwest vortex,the structure of low vortex circulation presented elliptic shape,and the southwest vortex cloud showed leaf-like or comma structures. When cold air in the behind of low vortex invaded,the typical ＂S＂boundary shape of low vortex cloud formed. So the structure and boundary shape had directive function for vortex formation,shift eastward and jet development.（ 3） There was a certain relationship between precipitation and low vortex cloud structure. When low vortex cloud presented leaf-like structure,precipitation center was located in the southeast of it,while when it presented comma structure,rainfall center was under the comma cloud.（ 4） The low vortex cloud precipitation had two stages in its life cycle. At the first stage,the precipitation occurred in warm region of low vortex. While at the second stage,the dry and cold air in middle level sunk intensively,and the convergence of cold air and warm air formed ＂人＂shape echo on radar reflectivity figure.