一次华南准静止线状对流系统触发维持机制研究

A study on triggering and maintenance mechanism of a linear quasi-stationary convection system in South China

2014年5月10日08时左右,在广东阳江市附近有分散对流单体出现并发展合并形成为尺度约200 km的准静止东西向线状MCS (Meso-scale Convective System),持续近16 h,造成广东阳江以东至珠江入海口以西沿海强降水。通过实况分析、WRF-ARW (the Advanced Research WRF)模式模拟及地形敏感试验发现,在有利的大尺度水汽热力条件背景下,特殊的中尺度动力热力结构与云雾山地形的持续相互作用是该MCS触发和维持机制的关键因素。在大气低层出现的SLLJ (Super-low Level Jet)构成了向北输送的暖湿气流"通道",增强了云雾山南侧上干冷与下暖湿的大气对流不稳定层结,使得暖湿空气在云雾山地形的阻挡作用下被强迫抬升达到自由对流高度,气块的CAPE (Convective Available Potential Energy)被触发释放,在云雾山附近生成分散的对流单体,配合中层偏西引导气流的作用,对流单体向东移动发展。由于以上大气中尺度动力热力结构特征的持续维持,配合云雾山地形抬升作用,在此后的十余小时内,云雾山附近不断触发新对流单体,在中层引导气流作用下向东移动的同时,持续的SLLJ为对流的发展供给大气不稳定能量使得对流单体逐渐发展合并,以此往复,形成了西端位于云雾山附近的准东西向线状MCS并长时间维持。

At about 08:00 on May 10, 2014, there were scattered convection cells evolving in the vicinity of Yangjiang, Guangdong Province of China. They merged into a quasi-linear-stationary meso-scale convective system(MCS) with the scale of about 200 km. This MCS lasted for almost 16 hours with a maximum rainfall of 372 mm. By analyzing observational data and conducting a terrain sensitive numerical simulation experiment, it is found that under a favorable large-scale water vapor thermal condition, the special meso-scale dynamic structure of continued interaction of the thermal structure with the Yunwu Mountain terrain is the key factor in the MCS triggering and maintenance mechanism. The night-enhanced super-low level jet(SLLJ) constitutes a“channel”for the warm and humid air flowing to the north, enhancing the unstable convective stratification, so that the warm and humid air was blocked by the mountain terrain and forced up to reach the free convection height, and the Convective Available Potential Energy(CAPE) of the air is triggered to release. Then dispersed convective cells emerged near the Yunwu Mountain, and moved eastward under the middle level leading wind. Due to the above-mentioned meso-scale dynamic thermal structural features with the topographical elevation of the Yunwu Mountain continuously existed, the linear quasi-stationary MCS formed and maintained for a long time.