浙江省春季至夏初飑线分型及对比分析

根据大尺度背景场的差异，将影响浙江省的七次飑线过程分为两种类型:冷涡类西北气流型和槽前西南急流型。通过环境场和雷达结构特征提炼异同点，结果表明:飑线系统发生在高空槽配合地面低压发展的有利环境场，对流层中高层相对干冷的平流叠加在低层暖湿气流之上，在对流发展区建立显著的条件不稳定层结。西北气流型由东亚大槽后干冷平流的强迫作用及925 hPa至地面辐合线触发产生，生命史长、强度强是主要特点；西南急流型飑线多发生在江淮低压冷锋南下型的地面形势场，西北东南移向的飑线主要由锋前低压系统内的冷暖交汇加上锋面抬升触发，而西南东北移向的飑线由西南急流强迫产生，低层西南急流脉动或风速辐合、地面辐合线等为触发抬升条件。T_850-500大于27 ℃，可以较好表征雷暴大风天气的环境场，B_li、B_CAPE等指示意义显著，而K指数和S_i指数对西北气流型飑线无指示意义。强的环境风垂直切变有利于飑线回波的组织化及回波垂直结构的倾斜；径向速度场的大风速区和MARC特征是飑线的共同特征，大风速区能直观地判断大风的位置和强度；阵风锋易出现在自北向南的强对流系统中，和阵风锋相交的回波强度强，持续久，易产生冰雹；冰雹回波在径向速度图上通常存在强的切变辐合或中气旋等共同特征。 

CLASSIFICATION AND COMPARATIVE ANALYSIS OF THE SQUALL LINES FROM SPRING TO EARLY SUMMER IN ZHEJIANG PROVINCE

According to the difference of large-scale background field, seven squall lines affecting Zhejiang Province are divided into two types: the type of northwest airflow from a cold vortex and the type of a pre-trough southwest jet stream. Based on the features of the environmental field and radar structure, the general features and individual differences are analyzed. The results show that the squall lines occurred in favorable environmental fields where a high-altitude trough worked with a surface low-pressure. Relatively dry cold advection from the middle and upper layer overlaid on a warm and humid airflow from the low-level, thus establishing a significant conditional unstable stratification in the convective development zone. The northwest airflow type is triggered by the force of dry cold advection from an East Asian deep trough and a low-level convergence line. The long history of life and strong intensity are the main features. The southwest jet type of squall line mostly occurs in a ground field where Jianghuai has a low-pressure system. The squall line moving from northwest to southeast is triggered by cold-warm convergence and frontal lift, while the squall line moving from southeast to northeast is forced by the southwest jet stream, and a low-level southwest jet pulsation or wind speed convergence and a ground convergence line are the triggering mechanism. The index of T850-500 can better characterize the environmental field of thunderstorm and gale weather. The convection indexes of Bli and BCAPE have good indication, while the K index and the Si index have no indication, for the cold vortex squall line. The strong environmental wind vertical shear is beneficial to the organization of the ridge echo and the tilting of the vertical structure of the echo. The large wind speed region and the MARC of the radial velocity field are common features of the squall line, which can help to judge the location and intensity of the windy area; the gust front is easy to appear in the strong convection system from north to south, and the echoes that intersect with the gust front become stronger and longer and easy to produce hail from. The hail echoes usually have strong upwind or medium cyclone characteristics on the radial velocity.