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《Chinese Journal of Atmospheric Sciences》 2018-05
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Observational and Numerical Analyses of a Squall Line Occurring over Liaodong Gulf of China

ZHANG Zhe;ZHOU Yushu;GAO Shouting;Key Laboratory of Cloud–Precipitation Physics and Severe Storms,Institute of Atmospheric Physics,Chinese Academy of Sciences;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences;  
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.
【Fund】: 国家重点基础研究发展计划(973计划)项目2014CB441402;; 国家自然科学基金项目41475054、41661144024、41475097、41575047;; 高原大气与环境四川省重点实验室开放课题PAEKL-2017-K2~~
【CateGory Index】: P445
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