成都盛夏短时强降水特征统计分析

Statistical Analysis of the Characteristics of Short-time Heavy Rainfall in Chengdu in July and August

利用成都市2017-2019年7-8月国家级自动站逐小时降雨量和常规探空分析了盛夏典型短时强降水过程的环流形势特征,建立了4种短时强降水概念模型.高空辐散、切变线和风向风速辐合、500hPa负变温、低空急流、500hPa负变高和地面中尺度辐合线是有利于短时强降水发生的大、中尺度影响系统.通过物理量分析可知,短时强降水发生在热力不稳定层结、中低层水汽充沛、垂直风切变弱、抬升凝结高度低和暖云层厚度较厚的环境中.绝大多数短时强降水回波(≥90%)为低质心的块状回波,平均持续时间接近30 min,移速以20~31 km·h^-1为主.在对流层低层,持续时间达3~12 h且风向较一致的显著偏南气流或偏东气流对短时强降水发生有较好的警示作用.700hPa偏南或偏北风对强降水回波的移动方向具有较好指示意义.

Hourly rainfall data obtained from 18 national meteorological stations and radiosonde data in July and August from 2017 to 2019 are used to analyze the environmental background and characteristics of short-time heavy rainfall processes that happened in Chengdu.Four different types of conceptual models are proposed.Results indicate that shorttime heavy rainfall processes are mostly happened under the synthetic influence of the large-scale and mesoscale systems,including the upper divergence,shear line,wind convergence,500 hPa temperature decline,low-level jet,500 hPa geopotential height decrement,and ground mesoscale convergence lines.By using the statistical analysis of physical parameters,conclusions can be drawn as follows.When short-time heavy rainfall occours,the thermal stratification is unstable and there are abundant atmospheric water vapor in middle and lower level,thick warm cloud layer,low lifing condensation level,weak vertical wind shear between 0 and 6 km.Most of radar echoes of short-time heavy rainfall(≥90%)have low centroid,for which the average duration is near 30 min and the moving speed is mainly 20-31 km·h^-1.Significant southerly or easterly wind with relatively consistent direction in lower troposphere which always lasts3 to 12 hours can often be a good indicator of short-time heavy rainfall.Similarly,southerly or northerly wind on 700 hPa can denote the moving direction of the strong radar echo in short-time heavy rainfall.