摘要:利用观测资料和高分辨率数值模拟资料对2014年6月26日发生在辽东湾北部的一次飑线过程进行了分析。本次飑线发生发展期间，对流层中层存在正在发展加深的槽，近地面则是偏南暖湿气流和西北干冷气流交汇形成的辐合线，天气尺度环境强迫较强，有利于强对流的触发和发展。此次飑线发生发展于地面辐合线的南段。对比分析表明模拟结果和实况观测较为一致。对辐合线北段对流较快消散，而南段对流得以继续发展成为飑线的原因进行了分析。结果表明，与北段相比，南段环境水汽更为丰富，对流有效位能大，水平风的垂直切变适宜。此外，南段环境还受海风锋导致的增湿、降温以及辐合带来的弱上升气流的影响。以上因素是导致辐合线北段对流较快消散而南段对流可以较长时间维持，并发展成为飑线系统的主要原因。本次飑线在成熟时期的气压场成显著的“高—低”结构分布。对流云区中部存在一个中高压，而尾流低压区位于对流云区后部与层状云区交界处。高压后部是一个强烈的地面辐散区，风速较大。飑线成熟时期中主要存在两支气流，前向入流在飑线前方低层流入，带入暖湿空气并在对流云区抬升，随后分成两支在飑线高层向前向后流出。后向入流在飑线后方中层流入，带入干冷空气并下沉，随后在近地面辐散流出。对飑线的对流云区、尾流低压区、层状云区及飑线后方的模拟探空展现了飑线不同区域的环境场特征。
关键词:飑线/
发展机理/
中尺度结构
Abstract:Results of the analysis based on observation and simulation of a squall line that occurred over Liaodong Gulf of China on 26 June 2014 are shown. The synoptic forcing was strong with a developing trough in the middle troposphere and a convergence line caused by the collision of moist and warm southerly flow and dry and cold northwesterly flow on the surface. The squall line was triggered and developed in the southern part of the surface convergence line. A high-resolution simulation of the squall line is carried out, which well reproduced the life cycle of the squall line. The study demonstrates the mechanism for different behaviors of the northern and southern parts of the convection, namely, while the northern part of the convection dissipated quickly, the southern part kept growing and evolved into a squall line. Results suggest that compared to that in the northern part, the moisture was more abundant and the environmental stratification was more unstable in the southern part, while the wind shear there was also more favorable for the development of the squall line. In addition, the sea-breeze front in the southern part helped to increase humidity, reduce temperature and induce weak updraft due to the convergence. All the above factors were accountable for different behaviors of the convection in the northern and southern parts. The pressure field of the squall line exhibited a significant "high-low" pattern in its mature stage. Namely, a meso-high was located in the convective region and a wake low was found in the transient region between convective and stratiform clouds. Strong divergence occurred in the rear of the meso-high, producing large surface winds. There were mainly two branches of flow in the squall line in its mature stage. A front-to-rear (FTR) inflow approached the squall line in the low-level from the front of the squall line, bringing in moist and warm air. The FTR inflow was lifted in the convective region, and split into two branches:an overturning outflow towards the front and an ascending outflow towards the rear in the high level. A branch of mid-level rear-to-front (RTF) inflow descended as it approached the squall line from the rear, bringing in cold and dry air. When it approached the surface, strong divergence occurred. Besides, simulated soundings of the squall line in the convective region, the wake low, the stratiform region and behind the squall line displayed different environment features in different regions of the squall line.
Key words:Squall line/
Developing mechanism/
Mesoscale structure
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