摘要
应用高分辨率中尺度数值模式WRF模拟了2007年8月8-9日陕西关中强暴雨过程,根据模式输出结果对强暴雨中尺度对流系统(MCS)的发生、发展规律、形成原因和三维结构,特别是暴雨过程中3个大暴雨中心的β中尺度对流系统(MβCS)的细微结构包括三维流场、动力和热力结构进行了分析。结果表明,此次强暴雨过程与一个α中尺度低涡的生成密切相关,其内部强烈发展的MβCS直接产生了岐山、礼泉、高陵3个强暴雨中心的对流降水;MβCS在850,700和500 hPa上分别表现为辐合(涡旋)系统、西北—东南向暖式切变线和阶梯槽。高空西风急流入口区右侧的动力强迫是对流层高层暴雨区辐散形成和加强的原因,动力强迫引起的非地转风是暴雨形成的原因之一;中空阶梯槽携带的干冷空气从后方流入雨团起到了对流不稳定的加强作用;低层和地面不同方向的风和风速形成的中尺度辐合以及中尺度西南急流和东南急流触发了强降水的发生,强降水的发生又激发了中尺度急流扰动,中尺度急流扰动对暴雨维持和加强起到了反馈作用;秦岭山脉的屏障作用和关中喇叭口地形的动力抬升作用有助于关中强暴雨的发生和加强。产生3个强暴雨中心的MβCS有不同的流场、动力、热力垂直结构:中低层不同方向和不同层次的气流流入β中尺度降水云塔,在不同高度上形成了不同的垂直环流支,云塔中的上升气流一直伸展到200 hPa(或150 hPa)后向东南、东北流出;歧山暴雨中心450 hPa以上为强辐散,450 hPa以下暴雨中心南侧为弱辐散和辐合、北侧为辐合和弱辐散,垂直上升运动先向南、后向北倾斜直至对流层顶;相当位温呈双高能中心形成的双重位势不稳定层结结构,温度则表现为中层两个暖中心、上下层冷中心的特征;礼泉和高陵暴雨中心为整层强上升运动柱与强散度柱和正涡度柱耦合,礼泉上升运动柱存在一个高、低层冷而中上层暖的特征,具有类似于地面气压场的鞍形结构,即中低层不稳定、中高层稳定、中层为中性的层结结构;高陵暴雨中心南缘550 hPa以下是高能量和温度离差锋区,其上空400 hPa以下为近饱和水汽柱。
A process of brief heavy rainfall on 8 -- 9 August 2007 in the central Shaanxi plain was simulated u- sing mesoscale model WRF with high resolution. The evolution, causes and three-dimensional structure of me- soscale convective system, especially the slight structural features of three rainstorm central meso-β-scale convec- tive system （MflCS） in the rainstorm process including three-dimensional stream field, dynamical and thermal structure were analyzed basing on model output. The results showed that the process of heavy rainstorm had fight relationship with development of a meso-α-scale vortex, in which the strong developing MβCS directly caused the three heavy rainstorm centers. MβCS showed as vortex, warm shear line and ladder trough on 850 hPa, 700 hPa and 500 hPa, respectively. The dynamical forcing of upper westerly jet right flank were possibly reason of divergent formation and strengthen, and ageostrophic wind caused by dynamical forcing was one of the reasons for the formation of rainstorm, and the ladder trough on 500 hPa played a role that carrying dry cold air inflow from the rear of rain group, which result in the strengthening of the convective instability, and the mesoscale convergence formed by the lower and ground wind in different directions and wind speed and mesoscale south- west jet and southeast jet triggered the occurrence of heavy precipitation, and the mesoscale jet disturbance was excited owing to occurrence of heavy rainfall, which played a feedback role to maintain and strengthen of rain- storm, and the barrier function of Qinling mountains and the dynamic lifting role of trumpet-shaped topography contributed to occurrence and enhancement of heavy precipitation. MβCS which bring three strong rainstorm cen- ters had different stream field, vertical dynamical and thermal structure. The vertical structure of the stream field given as follows： the air from different directions flowed into the meso-β-scale cloud tower in middle and lower troposphere, forming different vertical circulation circles in different layers; the updraft in cloud tower had been stretched to 200 hPa or 150 hPa and then turn to horizontal movement toward both southeast and northeast direc- tions out of the cloud tower. The vertical dynamical and thermal structure showed as. In Qishan： in middle re- gion of the meso-β-scale cloud tower, there were a strong divergence zone above 450 bPa, weak divergence or convergence zone at the south side of the meso-β-scale cloud tower and convergence or divergence zone at the north side of the meso-β-scale cloud tower below 450 hPa; the vertical lifting movement inclined to the south, then to the north, and finally to the tropopause. The potential equivalent temperature column appeared two high- energy centers, which brought about dual unstable stratification. The temperature bad a significant characteristic of vertical structure which there were two warm-corn in the middle layer and cold center in the upper and lower respectively. In the other two heavy precipitation centers in Liquan and Gaoling, the entire column of ascent movement was coupled with the strong divergence column, as well as the positive vorticity column. In Liquan, the lifting movement was a column with one strong warm center in the mid-high levels while cold in the high and low levels, which had the unstable stratification structure as ＇ the saddle＇ surface pressure field. In Gaoling, at the south edges of the meso-β-scale cloud tower, there were the： high, energy center and frontal zone of tempera- ture deviation below 550 hPa, saturated water vapor column bellow 400 hPa in middle region of the meso-β-scale cloud tower.
出处
《高原气象》
CSCD
北大核心
2014年第1期148-161,共14页
Plateau Meteorology
基金
北京局地暴雨中尺度对流系统研究(2010LASW-A05)
GRAPES中尺度模式的预报和改进(GYHY201006016)
关键词
强暴雨
数值模拟
中尺度系统
Brief heavy rainfall
Numerical simulation
Mesoscale system
