华中地区飑线统计和结构特征及有利生成环境条件的观测分析研究

Squall line, which is typically characterized by sudden onset, rapid evolution, and strong destruction, is quite difficult to be captured for further study using conventional data. Observational facts show that many strong squall line incidents happen in Central China in recent years, led to serious meteorological disasters. But the study of squall line in Central China is relatively insufficient. Based on the dense unconventional observation data over central and eastern regions in Hubei province, the statistical and structural characteristics of squall line and its attendant favorable environment conditions is investigated. Using radar mosaic data generated by SWAN system and surface automatic weather station data in Central China, the temporal and spatial statistical characteristics, 3-D echo structure characteristics, and mesoscale system characteristics on ground surface are analyzed. Based on reanalysis data, the circulation background, synoptic-scale effect systems, and water vapor transport before squall line occurred are researched, to reveal the effective weather conditions for the squall line formation in Central China. According to case study and composite analysis of squall line using microwave radiometer and wind profiler radar data with high temporal and vertical resolution, the relationship between squall line formation and the evolution of vertical wind shear, inversion layer, atmospheric instability indexes, and temperature, pressure, relative humidity, wind on ground surface are indicated. The relationship between squall line evolution and change of temperature, humidity, wind profile, and atmospheric instability indexes are also explored. This study is in order to enhance the understanding of statistical and structural characteristics of squall line in Central China and its attendant favorable environment conditions, to reveal the different characteristics of squall line in Central China, particularly to improve the forecasting ability of squall lines formation and evolution tendency.

飑线突发性强、演变迅速、破坏力大，常规资料难以研究，近几年的观测发现，华中地区发生多次强飑线事件，引发严重气象灾害，但针对此区域飑线的研究相对较少。项目依托湖北省中东部地区较为稠密的非常规观测网，展开飑线统计和结构特征及生成有利环境条件的研究。利用SWAN系统雷达回波和地面自动气象站资料，研究华中地区飑线时空统计特征和三维回波结构特征，地面中尺度系统特征；利用再分析资料，研究飑线发生前环流背景、天气尺度影响系统和水汽输送情况，揭示有利于华中地区飑线发生的天气条件；利用高时间和垂直分辨率的微波辐射计和风廓线雷达等资料，通过典型个例研究与多个例合成分析，明确垂直风切变、逆温层、不稳定指数的演变和地面温压湿风的突变与飑线生成的关系；探索飑线前方温湿风廓线及特征指数的变化与飑线演变之间的联系。项目意在加深对飑线特征及生成环境条件的认识，揭示华中地区飑线的差异性特征，提高其生成和演变趋势的预测能力。

突发性强、演变迅速的飑线常伴随严重气象灾害，由于观测资料匮乏，华中地区的飑线缺乏系统性研究。本项目基于高时空分辨率的雷达回波、地面自动站和探空数据、ERA5再分析资料，配合风廓线雷达和微波辐射计的数据，对华中地区近十年的飑线开展了统计工作，对其结构特征和生成发展的有利环境条件进行研究。主要成果如下：.1、结合前人定义及华中地区强对流天气特点，给出了华中地区飑线和“准飑线”的定义，统计近十年“准飑线”个例，明确了其时空分布、强度、尺寸、移速、形成和组织方式等特征量统计特征，建立了华中地区飑线数据库。.2、对达到飑线标准的个例展开细致研究，发现飑线走向与移动方向之间的联系；TS型飑线尺度更大，对流发展的更强、更高，回波中心更低；飑线的组织方式和形成方式之间并无明显的对应关系。.3、华中飑线有台风型、槽后型、槽前型3类。台风型受台风暖湿气流影响，水汽供应量最充足；槽后型受西北冷空气影响，水汽供应量很少；槽前型水汽均来自南海地区，受到中层低涡和切变线、辐合线影响，低空急流和边界层急流作用显著。飑线移动方向与中层气流基本一致或在其右侧。华中地区飑线水汽条件相对较差，但对流不稳定性更高，且易向不稳定性更大的地方移动。.4、绝大多数飑线伴随显著的地面大风，风向与飑线移动方向一致或略偏右，TS型飑线大风的范围更大，强度更强；TS型飑线经过的站点出现了地面气压的涌生，PS型飑线则有部分站点没有；但所有类型的飑线移动路径上都出现了明显的冷池。.5、飑线生成之前南侧环境风随高度逆转，飑线越发展，低层风速越大，北侧边界层内环境风由强的偏南风转为偏北风。TS类飑线生成前边界层内的水汽密度增加的更早，飑线生成前出现突增，并向高层扩展；PS类飑线水汽密度增加集中在边界层。.项目成果加深了对华中飑线特征及生成环境条件的认识，明确了飑线生成前物理量的演变特征，这对提高飑线预报预警和灾害防护工作能力具有积极意义。