摘要
利用常规观测资料、地面加密自动站、多普勒雷达等多种观测资料以及雷达变分同化分析系统(VDRAS)的高分辨率分析场资料,对2012年7月21日发生在北京的全市性大暴雨、局地特大暴雨的系统结构演变特征及成因进行了初步分析。结果表明:(1)此次降水过程分为两个阶段,第一阶段在21日10—20时,呈现出短时雨强大且波动性显著的对流性降水特点,第二阶段降水在21日20时—22日04时,降水相对平缓,表现为锋面降水特征。(2)21日天气尺度环流形势场配置满足华北暴雨的典型背景条件:高空急流形成的辐散与对流层中低层的低涡、切变线及地面倒槽构成的深厚辐合区,形成强烈垂直运动并持续维持的机制,造成了长达16 h的强降水过程;副热带高压外围的东南水汽通道和西南低空急流的水汽输送为暴雨发生提供了充沛水汽条件。(3)大暴雨过程第一阶段降水回波具有明显的"列车效应"传播特征",列车效应"的初始对流起源于地形强迫造成的暖区内中尺度辐合以及低空急流增强过程中的风速脉动;中尺度对流单体沿低空急流轴左侧传播,具有明显的重力波传播特征,西南急流的稳定维持使惯性重力波不断从背景场中获得能量并不断发展。(4)地形对降水有明显的增幅作用,边界层内长时间维持的东南风在太行山脉前与西南风和东北风交汇,在山前形成辐合带并长时间维持,有利于水汽积聚;山脉的阻挡使东南气流在迎风坡爬坡抬升,从而加大了山前区域的降水量。
The synoptic configuration features and contributing factors of a torrential rain occurring in Beijing region on 21 July 2012 have been preliminarily investigated by using conventional observation data, intensive automatic weather station observations, Doppler-Radar data etc. and low-level thermal and dynamical retrieval system of 4Dvar based on Variational Doppler Radar Analysis System （VDRAS）. The con- clusions are drawn as follows. （1） There are two stages during the torrential rain. The first one is from 10 a.m. to 20 p.m. （LTC） on 21 July 2012 and presents convective precipitation with short-time, high rainfall intensity and obvious fluctuation. The second one is from 20 p.m. on 21 July to 04 a.m. on 22 July 2012 and presents smooth frontal precipitation. （2） The synoptic scale circulation situations on 21 July are typical circulation pattern of North China heavy rain. The divergence caused by high-level jet, low-vortex and shear in the lower and middle tropo- sphere, and deep convergence zone triggered by surface inverted trough cause the formation and continuance of strong vertical upward motion, which lead to 16 h severe precipitation process. The southeast moisture channel at the periphery of subtropical high and the southwesterly low-level jet supply sufficient moisture condition for the occurrence of torrential rain. （3） The precipitation echoes in the first stage of the pro- cess have an obvious train effect whose initiate convection originates from both mesoscale convergences in warm regions caused by topograph- ic forcing effect and wind velocity fluctuation in the enhancing process of low-level jet. The mesoscale convective cells moving along the left side of low-level jet axle have a significant gravity wave transmitting feature. The stable continuance of southwesterly jet made inertia-gravitational wave ohtain energy from amhient field and develop continuously. （4） Topography promotes precipitation increment. The southeast wind in boundary layer joins southwest wind or northeast wind in front of the Taihang Mountain and forms a continuing eonvergenee zone in front of lhe mountains, which is in rawer of the accumnlation of vapor, meanwhile, the southeast airflow is uplifted at the windward slope of lhe mountains, whieh leads to the increase of precipitation in the regions in front of the mountains.
出处
《暴雨灾害》
2012年第3期218-225,共8页
Torrential Rain and Disasters
基金
公益性行业(气象)专项"华北暴雨发生发展特点及预报技术研究"(GYHY200906011)
国家支撑项目"城市群高影响天气的特征和成因分析"(2008BAC37B01)
北京市科技计划项目"极端天气事件对城市安全运行的影响评估系统研究"
中国气象局"全国强对流预报创新团队"项目
关键词
大暴雨
系统结构
列车效应
地形
重力波
成因初探
torrential rain
synoptic configuration
train effeet
terrain
inertial gravity wave
mechanism analysis
