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Evolution Mechanism of a Severe Squall Line Triggered by the Coupling of a Sea Breeze front and a gust front

Journal of Tropical Meteorology 2024年第2期30卷 200-210页

作者：万夫敬孙敏庞华基赵海军赵传湖 Qingdao Meteorological Bureau QingdaoShandong 266003 China Shanghai Central Meteorological Observatory Shanghai 200030 China Linyi Meteorological Bureau LinyiShandong 276037 China frontier Science Center for Deep Ocean Multispheres and Earth System(FDOMES)and Physical Oceanography Laboratory Ocean University of ChinaQingdaoShandong 266101 China

In the present study, a severe squall line(SL) was analyzed by using intensive observational surface data and radar monitoring products. In this process, mesoscale convergence lines, such as the sea breeze front(SBF), gust front and dry line, served as the main triggering and strengthening factors. The transition from convection triggering to the formation of the initial shape was mainly affected by the convergence line of the SBF, which combined with thermal convection to form the main parts of the SL. In the later stage, the convergence line of the gust front merged with other convergence lines to form a series of strong convective cells. The SBF had good indicative significance in terms of severe convective weather warnings. The suitable conditions of heat, water vapor and vertical wind shear on the Shandong Peninsula were beneficial to the maintenance of the SL. Before SL occurrence, tropopause folding strengthened, which consequently enhanced the baroclinic property in the middle and upper troposphere. The high sensible heat flux at the surface easily produced a positive potential vorticity anomaly in the low layer, resulting in convective instability, which was conducive to the maintenance of these processes. In the system, when precipitation particles passed through the unsaturated air layer, they underwent strong evaporation, melting or sublimation, and the cooling effect formed negative buoyancy, which accelerated the sinking of the air and promoted the sustained development of the surface gale. Together with the development of lowlevel mesocyclones, the air pressure decreased rapidly, which was conducive to gale initiation.

关键词： squall line sea breeze front gust front cold pool thunderstorm gale

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gust front Statistical Characteristics and Automatic Identification Algorithm for CINRAD

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Journal of Meteorological Research 2014年第4期28卷 607-623页

作者：郑佳锋张杰朱克云刘黎平刘艳霞 Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration Nanjing University of Information Science & Technology State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences College of Atmospheric Sciences Chengdu University of Information Technology Air Force Meteorological Center in Chengdu Fuzhou Meteorological Bureau

gust front is a kind of meso-and micro-scale weather phenomenon that often causes serious ground wind and wind shear. This paper presents an automatic gust front identification algorithm. Totally 879 radar volume-scan samples selected from 21 gust front weather processes that occurred in China between 2009 and 2012 are examined and analyzed. gust front echo statistical features in reflectivity, velocity, and spectrum width fields are obtained. Based on these features, an algorithm is designed to recognize gust fronts and generate output products and quantitative indices. Then, 315 samples are used to verify the algorithm and 3 typical cases are analyzed. Major conclusions include： 1） for narrow band echoes intensity is between 5 and 30 dBZ, widths are between 2 and 10 km, maximum heights are less than 4 km （89.33%are lower than 3 km）, and the lengths are between 50 and 200 km. The narrow-band echo is higher than its surrounding echo. 2） gust fronts present a convergence line or a wind shear in the velocity field;the frontal wind speed gradually decreases when the distance increases radially outward. Spectral widths of gust fronts are large, with 87.09% exceeding 4 m s-1 . 3） Using 315 gust front volume-scan samples to test the algorithm reveals that the algorithm is highly stable and has successfully recognized 277 samples. The algorithm also works for small-scale or weak gust fronts. 4） Radar data quality has certain impact on the algorithm.

关键词： gust front statistical characteristics identification algorithm narrow-band echo

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Atypical Occlusion Process Caused by the Merger of a Sea-breeze front and gust front

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Advances in Atmospheric Sciences 2015年第10期32卷 1431-1443页

作者： Abuduwaili ABULIKEMU XU Xin WANG Yuan DING Jinfeng WANG Yan Key Laboratory of Mesoscale Severe Weather(Ministry of Education) School of Atmospheric SciencesNanjing University Tianjin Weather Modification Office

An atypical occlusion process that occurred in North China on 14 July 2011 is studied based on both observations and a real-data Weather Research and Forecasting （WRF） model simulation. The results show that this atypical occlusion process was significantly different from the traditional, synoptic-scale occlusion process that occurs within extratropical cyclones. It was caused by the merger of two cold-type mesoscale fronts. One of the fronts developed from the gust front of convective storms, while the other was a sea-breeze front. As the two fronts moved towards each other, the warm air between them was squeezed and separated from the surface. An atypical occluded front was formed when the two fronts merged, with the warm air forced aloft. This kind of occlusion is termed a ＂merger＂ process, different from the well-known ＂catch-up＂ and ＂wrap-up＂ processes. Moreover, local convection was found to be enhanced during the merger process, with severe convective weather produced in the merger area.

关键词： occlusion process sea-breeze front gust front merger

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The scattering mechanism of squall lines with C-Band dual polarization radar.Part Ⅰ:echo characteristics and particles phase recognition

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frontiers of Earth Science 2022年第2期16卷 221-235页

作者： Jiashan ZHU Ming WEI Sinan GAO Hanfeng HU Lei MA Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science&TechnologyNanjing 210044China Leihua Electronic Technology Research Institute of Aviation Industry Corporation of China Wuxi 214063China

Squall line is a kind of common mesoscale disaster weather.At present,there are few studies on the elaborate detection of squall line by dual polarization radar.With the dual polarization upgrade of weather radar network,we need to study the relationship between squall line echoes of base data and polarization data to reveal new echo phenomena and formation mechanisms.The relationship between radar parameters and atmospheric physical processes also need to be examined.Based on the NUIST CDP radar,a squall line in the Yangtze and Huaihe River basin that occurred from July 30 to 31,2014 is analyzed.The results show that polarization parameters have obvious advantages in the characteristics analysis of size,phase state,shape and orientation of the water condensate particles.The phase states of water condensate particles in convection cell can be distinguished through comparative discussion.Several phase states exist in the squall line,including small,medium and large raindrops,melting hails,dry hails and ice crystal particles and the Z_(DR)column can be used to identify the location of the main updraft.In addition,the polarization parameters are more sensitive to the melting layer.The gust front is presented as a narrow linear echo in Z affected by strong turbulence.It is an obvious velocity convergence line in V and approximately 0.70 inρ_(HV).The Z_(DR)can be used as a criterion to distinguish the horizontal and vertical scale of turbulence.The deforming turbulence,which is affected by environmental airflow,will cause an abnormally high Z_(DR)in the gust front and a negative Z_(DR)before and after the gust front.The variation of Z_(DR)depends on the turbulence arrangement,orientation and relative position between turbulence and radar.These dual polarization parameter characteristics offer insights into understanding the structure and evolution of the squall line.

关键词： dual polarization Doppler radar RHI squall line gust front turbulence

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