渤海西岸暴雨中尺度对流系统的结构及成因

The Structure and Origin of a Rainstorm-inducing Mesoscale Convective System on Western Coast of Bohai Bay

利用卫星、雷达和加密自动站等监测资料,结合VDRAS系统资料和1°×1°NCEP再分析资料,对造成黑昼和暴雨的中尺度对流系统的空间、热动力结构特征和发生、发展及维持原因进行了分析。结果表明:2004—2009年渤海西岸圆形α-中尺度对流系统有别于南方,其中只有16%可发展为中尺度复合体;黑昼现象是影响系统的特殊性所致。突发性暴雨的制造者是α-中尺度对流系统西端不断新生的β-中尺度对流系统,其发生、发展、维持与边界层内冷池外流、对流层低层(1.3～2.4 km)侵入的西北气流与西南气流形成的辐合线或交汇线有密切关系。α-中尺度对流系统的上升速度中心在500 hPa附近,多个β-中尺度对流系统分别具有独自的垂直气流和弱边界层环流。α-中尺度对流系统内部扰动温度呈下负上正的垂直分布,促使了不稳定层结趋于稳定;冷池呈东厚西薄的楔形结构,有利于β-中尺度对流系统发展维持。

Black day phenomenon and sudden hard rain occur in Tianjin on 16 June 2009.Based on several monitoring data such as FY-2 satellites data,multi-radar composite and intensive automatic stations data,combing with VDRAS data,the origins of black day and the rainstorm are analyzed.The thermal and dynamical structure which leads to the occurrence and development of mesoβ-scale,mesoγ-scale convective systems in circular meso-α-scale convective system are also studied.31 circle-shape MCSs which lead to severe weather on western coast of Bohai Bay in 2004—2009 are preliminarily sorted and summed up in size and life-circle. Less than 16%circular MαCS on the western coast of Bohai Bay develop into MCC with no more than 15×10~4 km^2 large（where the TBB is equal to or below -52℃）.The MCCs generally last no more than 8 hours and always happen in night.But in the South China,it＇s common to see MCC larger than 20×10~4 km^2 which last more than 10 hours.＂6.16＂MαCS has special characteristics in range,time of occurrence and precipitation echoes on the thickness,which are the main causes for black day phenomenon.New MβCS and MγCS develop constantly in the west of MαCS move eastward into the high energy region with warm-moisture intensively and maintain, leading to rainstorm in Tianjin. Cold air intrudes into MαCS from its back at the height of 1.3 - 2.4 km.flows out from rain echoes convergence line or close-gradually line,and triggers the development of MβCS with southwestern warmmoisture flow. In the ascending center of MαCS,the vertical velocity is 0.7 Pa·s（？） at height of 500 hPa.Below the height of 700 hPa（about 3 km）,ascending vertical velocity reaches 1.8 m·s（？）,and each of MβCS1-3 has independent vertical circle.Under the height of 1 km,there is corresponding boundary layer circulation for MβS1-3.With evolution of MβCS1—3,cold pool（the areas of negative perturbation temperature） appears under the height of 2 km and the area of positive perturbation temperature appears above it, so the vertical structure is stable.