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长沙一次大暴雨的双偏振及风场反演特征分析
唐明晖1,2, 付炜3, 罗源1, 周慧1,2, 蔡荣辉1,2
1. 湖南省气象台,湖南 长沙 410118;2. 气象防灾减灾湖南省重点实验室,湖南 长沙 410118;3. 株洲市气象局,湖南 株洲 412000
摘要:
利用 S波段双偏振雷达和 X波段相控阵雷达对 2022年 4月 25日长沙大暴雨过程进行分析。(1)回波带由东北-西南向带状演变成东-西向带状,差分反射率因子(ZDR)大值区(≥1.0 dB)呈带状分布,列车效应造成长沙大暴雨天气过程。(2)过程对流单体东-西向排列且强回波(≥45 dBZ)扩展至 6 km,ZDR、差分相移率(KDP)柱扩展至融化层高度以上;对流单体融化层高度以下 ZDR大部分为正值,且底层 ZDR、KDP大值区说明雨滴不仅水平直径大且数浓度高,对应雨强大。(3)分钟雨量超过 1 mm 对应 1.7~2.4 °·km-1 KDP值,且出现 KDP空洞;分钟雨量超过 2 mm 对应 2.4~3.1 °·km-1 KDP值。(4)三维风场显示强降水期间,带状对流回波前侧、南侧强西南风为大暴雨源源不断输送水汽;较深厚的辐合有利于带状回波维持;弓型回波伴有气旋式风场;高层风场有强辐散。(5)三维风场和强度垂直剖面显示最强降水时段有明显云砧回波,有利的动力抬升和水汽输送使得强回波中心M得以维持;随着中低层逐渐转为西北风或西风,回波减弱、分钟雨量陡降。以上分析结果表明双偏振产品对对流性降雨有明显的指示意义,X波段相控阵雷达反演的三维风场较好地刻画了对流强度及辐合、辐散特征。
关键词:  大暴雨  双偏振雷达  相控阵雷达  列车效应  ZDR  KDP
DOI:10.16032/j.issn.1004-4965.2024.055
分类号:
基金项目:
Analysis of Dual Polarization and Wind Field Inversion Characteristics of a Heavy Rainstorm in Changsha
TANG Minghui1,2, FU Wei3, LUO Yuan1, ZHOU Hui1,2, CAI Ronghui1,2
1. Hunan Meteorological Observatory, Changsha 410118, China;2. Key Laboratory of Preventing and Reducing Meteorological Disaster of Hunan Province, Changsha 410118, China;3. Zhuzhou Meteorological Bureau, Zhuzhou, Hunan 412000, China
Abstract:
This study aims to help forecasters to apply dual polarization and phased array radar products in the analysis of rainstorm process. The heavy rainstorm in Changsha on April 25, 2022, is analyzed by using S-band dual-polarization radar and X-band phased-array radar. The findings are as follows: (1) The precipitation echo belt changed from a northeast-southwest orientation to an east-west orientation. The high value region(≥1.0 dB) of difference reflectance factor (ZDR) showed zonal distribution, and the train effect caused the heavy rain in Changsha. (2) Multiple convective cells were arranged in an east-west direction and extended to a height of 6km. The expansion of ZDR and KDP columns above the height of the melting layer indicated that strong upward airflow provided favorable conditions for water droplets to break through the melting layer and form supercooled water droplets. Below the height of the melting layer of convective cells, most ZDR values were positive, with noticeable high values of ZDR and KDP in the bottom layer. This indicated large horizontal raindrop diameters and high number concentrations, corresponding to strong rainfall. (3) When minute rainfall exceeded 1 m, KDP ranged from 1.7 ° to 2.4 ° · km-1, and KDP cavities appeared. When minute rainfall exceeded 2 mm, KDP ranged from 2.4 ° to 3.1 ° · km-1. (4) The three-dimensional wind field of phased-array radar inversion showed that during the heavy precipitation, strong southwest wind in front and south of the zonal precipitation echo carried water vapor, contributing to the heavy rain process. The deep shear line facilitated the maintenance of banded echo, with a strong bow echo accompanied by cyclonic wind fields and strong divergence in the upper wind field. Guided by the airflow, the banded echo continuously passed through Changsha, forming the train effect. (5) The vertical section of three-dimensional wind field and intensity showed distinct anvil-shaped echoes during the heaviest precipitation period. The strong echo center was influenced by power lift and water vapor transport conditions. As winds changed to the northwest or west at mid-low levels, the echo gradually weakened, and minute rainfall decreased sharply. The above analysis indicates that dual polarization products can help indicate convective rainfall, and the three-dimensional wind field retrieved by X-band phased array radar effectively depicts the characteristics of convective intensity, convergence, and divergence.
Key words:  heavy rain  dual-polarization radar  phased-array radar  train effect  ZDR  KDP
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