山东半岛一次台风暴雨过程的冷空气侵入特征分析

Characteristic analysis of cold air intrusion during a typhoon-related torrential rain event in Shandong Peninsula

利用FY-2E卫星水汽图像、常规观测资料和NCEP/NCAR 1°×1°再分析资料,针对山东半岛一次与台风相关的大暴雨事件中干冷空气的侵入特征进行分析。结果表明:台风北上与极地大陆气团交汇,是导致此次大暴雨发生的重要因素。干冷空气从西侧侵入台风环流,台风变性,斜压锋生,位能向动能转换,导致上升运动加强,有利于产生强降水。冷空气具有高位涡和低湿度的特点,水汽图像上的暗区、高层等熵面上的干区和高位涡区有良好的对应关系。水汽图像直观地反映了此次大暴雨过程的系统演变过程。台风云系与斜压叶状云结合,先形成新的涡旋云系,后演变成逗点云型。暗区指示的干冷空气不断发展,先形成干舌,后以干缝的形式卷入涡旋中心。在实际预报中,除了流型识别外,通过水汽图像还可以追踪干湿区及其边界等变化特征。通过连续时次的对比分析,可监测高空动力强迫,判断灾害性天气系统的发展演变。

By employing conventional observation data, NCEP/NCAR 1°×1° reanalysis data, as well as FY-2E water vapor images, the characteristics of cold air intrusion during a typhoon-related torrential rain event in Shandong Peninsula is analyzed. Results reveal that the typhoon, moving northward and being coalesced with continental polar air, was a major contributing factor to the torrential rain. The cold and dry air intruded into the typhoon circulation from the west side, induced baroclinic frontogenesis and extratropical transition of typhoon, and resulted in transition from baroclinic potential energy to kinetic energy and the strengthening of the ascending motion. The cold air was characterized by high potential vorticity and low humidity. Dark zones in water vapor satellite imageries corresponded well with the areas of low humidity and high potential vortieity in high isentropic surface. Satellite imagery in the water vapor channel directly demonstrated the process of system evolution. The combination of typhoon circulation and baroclinie leaf was firstly developed into a new vortex and then a comma cloud. Water vapor dark zones associated with cold and dry air constantly developed from dry tongue to dry slot, which was drawn into the center of the vortex. Besides the identification of flow pattern, by analyzing water vapor images, the characteristics of dry or moist zone and their boundaries can also be clearly identified. Comparison analysis of continuous water vapor images provides the forecaster with additional information on dynamic properties in high levels, which is especially helpful when issuing severe weather warnings.