冷空气在北上台风“利奇马”致灾暴雨中的作用分析

利用NCEP逐6 h再分析资料、地面加密观测、探空、雷达资料,分析得出“利奇马”致灾暴雨是在长时间稳定维持的天气尺度环流背景下形成的。冷空气在降水所起的作用表现在:(1)长时间维持的弱冷空气与偏南暖湿气流交汇形成了边界层辐合线,辐射升温和暖湿气流的输送加大了辐合线两侧的温度和露点梯度,在高温高湿的有利环境下,对流在辐合线附近强烈发展。(2)高空槽后冷空气由“利奇马”环流西北侧渗入,先后形成3个冷平流中心,分别对应3个阶段的降水。(3)冷暖空气在降水区的持续辐合抬升作用增强了降水,最强降水时段发生在锋区垂直方向坡度最大的时段。(4)水平锋生有利于水汽输送和辐合抬升,垂直锋生有利于对流不稳定能量的累积和触发。冷空气形成的水平辐合和抬升造成大范围上升运动,使得锋生和垂直锋消同时存在,最强降水时段发生在水平锋生最强的时段。

Analysis of the role of cold air in the rainstorm caused by Typhoon“Lichma”

By using NCEP reanalysis data,ground encryption observations,sounding,and radar data,the analysis shows that the"Lichma"disaster-causing rainstorm is formed under the background of a long-term stable synoptic circulation background.The role of cold air in this precipitation is as follows:(1)In favor of the warm and wet environment,convection develops strongly near the convergence line which formed by the long-term maintenance of weak cold air and the southerly warm and humid air flow.The temperature and dew point gradients on both sides of the convergence line are increased by the radiation heating and the transport of the warm and humid air.(2)The cold air from the high trough infiltrates from the northwest side of the“lichtma”circulation,forming three cold advection centers successively corresponding to three stages of precipitation.(3)The strong convergence and uplift enhance the precipitation.The strongest precipitation occurs in the period of the maximum vertical slope in the front area.(4)Horizontal frontogenesis is conducive to water vapor transportation and convergence uplift,while vertical frontogenesis is conducive to the accumulation and triggering of convective instability energy.The horizontal convergence and uplift of cold air results in a large range of upward movement,which makes frontogenesis and vertical front dissipation exist at the same time.The strongest precipitation period occurs in the strongest period of horizontal frontogenesis.