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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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squall line and Its Vertical Motion Under Different Moisture Profiles in Eastern China

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Journal of Tropical Meteorology 2020年第3期26卷 321-335页

作者： ZHENG Lin-lin SUN Jian-hua ZHANG Jiao QIU Xue-xing YAO Chen Anhui Meteorological Observatory Hefei 230031 China Anhui Institute of Meteorological Sciences Hefei 230031 China Anhui Province Key Laboratory of Atmospheric Science and Satellite Remote Sensing Hefei 230031 China Institute of Atmospheric Physics Chinese Academy of SciencesBeijing 100029 China University of Chinese Academy of Sciences Beijing 100049 China

The impacts of different moisture profiles on the structure and vertical motion of squall lines were investigated by conducting a set of numerical *** base state was determined by an observational sounding,with high precipitable water representing moist environmental conditions in the East Asian monsoon *** reveal the impact of moisture at different levels,the moisture content at the middle and low levels were changed in the numerical *** numerical results showed that more convective cells developed and covered a larger area in the high moisture experiments,which was characteristic of the convection during the Meiyu season in *** addition,high moisture content at low levels favored the development of updrafts and triggered convection of greater *** was demonstrated by the thermodynamic parameters,including Convective Available Potential Energy(CAPE),Lifted Index(LI),Lift Condensation Level(LCL),and Level of Free Convection(LFC).Dry air at middle levels led to strong downdrafts in the environment and updrafts in *** could be because dry air at middle levels favors the release of latent heat,thereby promoting updrafts in clouds and downdrafts in the ***,high relative humidity(RH)at low levels and low RH at middle levels favors updrafts in the cloud ***,moist air at low levels and dry air at middle levels promotes the development of convective cells and the intensification of cold *** squall line can be organized by the outflow boundary induced by cold *** balance of cold pool and environmental wind shear is favorable for the maintenance and strengthening of squall lines.

关键词： squall line numerical simulation precipitable water downdraft latent heat cold pool

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Moisture Analysis of a squall line Case Based on Precipitable Water Vapor Data from a Ground-Based GPS Network in the Yangtze River Delta

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Advances in Atmospheric Sciences 2007年第3期24卷 409-420页

作者：丁金才杨引明叶其欣黄炎马晓星马雷鸣 Y. R. GUO Shanghai Meteorological Center Shanghai 200030 Shanghai Remote Sensing and Measurement Application Center Shanghai Typhoon Institute Shanghai 200030 National Center for Atmospheric Research CO USA

A squall line swept eastward across the area of the Yangtze River Delta and produced gusty winds and heavy rain from the afternoon to the evening of 24 August 2002. In this papers the roles of moisture in the genesis and development of the squall line were studied. Based on the precipitable water vapor （PWV） data from a ground-based GPS network over the Yangtze River Delta in China, plus data from a Pennsylvania State University/National Atmospheric Center （PSU/NCAR） mesoscale model （MM5） simulation, initialized by three-dimensional variational （3D-VAR） assimilation of the PWV data, some interesting features are revealed. During the 12 hours prior to the squall line arriving in the Shanghai area, a significant increase in PWV indicates a favorable moist environment for a squall line to develop. The vertical profile of the moisture illustrates that it mainly increased in the middle levels of the troposphere, and not at the surface. Temporal variation in PWV is a better precursor for squall line development than other surface meteorological parameters. The characteristics of the horizontal distribution of PWV not only indicated a favorable moist environment, but also evolved a cyclonic wind field for a squall line genesis and development. The ＂＋2 mm＂ contours of the three-hourly PWV variation can be used successfully to predict the location of the squall line two hours later.

关键词： squall line global positioning system (GPS) precipitable water vapor (PWV)

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Convective Scale Structure and Evolution of a squall line Observed by C-Band Dual Doppler Radar in an Arid Region of Northwestern China

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Advances in Atmospheric Sciences 2010年第5期27卷 1099-1109页

作者：刘黎平庄薇张芃菲牟容 The State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences CIMMS University of Oklahoma Norman Oklahoma USA

A long-lived and loosely organized squall line moved rapidly across U¨ru¨mqi, the capital city of Xinjiang Uygur Autonomous Region of China on 26 June 2005, generating hail and strong winds. The squall line was observed by a dual Doppler radar system in a field experiment conducted in 2004 and 2005 by the Chinese Academy of Meteorological Sciences and the local meteorological bureau in northwestern China. The 3D wind fields within the squall line were retrieved through dual Doppler analyses and a variational Doppler radar analysis system （VDRAS）. The formation and structure of the squall line as well as the genesis and evolution of embedded convective cells were investigated. During its life period, the squall line consisted of six storm cells extending about 100 km in length, and produced hail of about 25 mm in diameter and strong surface winds up to 11 m s^-1. Radar observations revealed a broad region of stratiform rain in a meso-β cyclone, with the squall line located to the west of this. Two meso-γ scale vortices were found within the squall line. Compared to typical squall lines in moist regions, such as Guangdong Province and Shanghai, which tend to be around 300–400 km in length, have echo tops of 17–19 km, and produce maximum surface winds of about 25 m s^-1 and temperature variations of about 8-C this squall line system had weaker maximum reflectivity （55 dBZ）, a lower echo top （13 km） and smaller extension （about 100 km）, relatively little stratiform rainfall preceding the convective line, and a similar moving speed and temperature variation at the surface.

关键词： dual Doppler radar convective scale squall line

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Assimilating Surface Observations in a Four-Dimensional Variational Doppler Radar Data Assimilation System to Improve the Analysis and Forecast of a squall line Case

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Advances in Atmospheric Sciences 2016年第10期33卷 1106-1119页

作者： Xingchao CHEN Kun ZHAO Juanzhen SUN Bowen ZHOU Wen-Chau LEE Key Laboratory for Mesoscale Severe Weather/MOE and School of Atmospheric Science Nanjing UniversityNanjing 210046China National Center for Atmospheric Research BoulderColorado 80301USA

This paper examines how assimilating surface observations can improve the analysis and forecast ability of a four- dimensional Variational Doppler Radar Analysis System （VDRAS）. Observed surface temperature and winds are assimilated together with radar radial velocity and reflectivity into a convection-permitting model using the VDRAS four-dimensional variational （4DVAR） data assimilation system. A squall-line case observed during a field campaign is selected to investigate the performance of the technique. A single observation experiment shows that assimilating surface observations can influence the analyzed fields in both the horizontal and vertical directions. The surface-based cold pool, divergence and gust front of the squall line are all strengthened through the assimilation of the single surface observation. Three experiments--assimilating radar data only, assimilating radar data with surface data blended in a mesoscale background, and assimilating both radar and surface observations with a 4DVAR cost function--are conducted to examine the impact of the surface data assimilation. Independent surface and wind profiler observations are used for verification. The result shows that the analysis and forecast are improved when surface observations are assimilated in addition to radar observations. It is also shown that the additional surface data can help improve the analysis and forecast at low levels. Surface and low-level features of the squall line-- including the surface warm inflow, cold pool, gust front, and low-level wind--are much closer to the observations after assimilating the surface data in VDRAS.

关键词： VDRAS 4-D data assimilation radar data surface data squall line

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The Predictability of a squall line in South China on 23 April 2007

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Advances in Atmospheric Sciences 2013年第2期30卷 485-502页

作者：吴多常孟智勇严大春 Laboratory for Climate and Ocean-Atmosphere Studies Department of Atmospheric and Oceanic Sciences School of PhysicsPeking University

This study investigated the predictability of a squall line associated with a quasi-stationary front on 23 April 2007 in South China through deterministic and probabilistic forecasts. Our results show that the squallline simulation was very sensitive to model error from horizontal resolution and uncertainties in physical parameterization schemes. At least a 10-km grid size was necessary to decently capture this squall line. The simulated squall line with a grid size of 4.5 km was most sensitive to long-wave radiation parameterization schemes relative to other physical schemes such as microphysics and planetary boundary layer. For a grid size from 20 to 5 km, a cumulus parameterization scheme degraded the squall-line simulation （relative to turning it off）, with a more severe degradation to grid size -10 km than 〉10 km. The sensitivity of the squall-line simulation to initial error was investigated through ensemble forecast. The performance of the ensemble simulation of the squall line was very sensitive to the initial error. Approximately 15% of the ensemble members decently captured the evolution of the squall line, 25% failed, and 60% dislocated the squall line. Using different combinations of physical parameterization schemes for different members can improve the probabilistic forecast. The lead time of this case was only a few hours. Error growth was clearly associated with moist convection development. A linear improvement in the performance of the squall line simulation was observed when the initial error was decreased gradually, with the largest contribution from initial moisture field.

关键词： squall line predictability South China ensemble moisture

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Analysis of the Structure and Propagation of a Simulated squall line on 14 June 2009

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Advances in Atmospheric Sciences 2015年第8期32卷 1049-1062页

作者： LIU Lu RAN Lingkun SUN Xiaogong Institute of Atmosphere Physics Chinese Academy Sciences Graduate University of Chinese Academy of Sciences Chinese Academy of Meteorological Sciences

A squall line on 14 June 2009 in the provinces of Jiangsu and Anhui was well simulated using the Advanced Regional Prediction System （ARPS） model. Based on high resolution spatial and temporal data, a detailed analysis of the structural features and propagation mechanisms of the squall line was conducted. The dynamic and thermodynamic structural charac- teristics and their causes were analyzed in detail. Unbalanced flows were found to play a key role in initiating gravity waves during the squall line＇s development. The spread and development of the gravity waves were sustained by convection in the wave-CISK process. The squall line＇s propagation and development mainly relied on the combined effect of gravity waves at the midlevel and cold outflow along the gust front. New cells were continuously forced by the cold pool outflow and were enhanced and lifted by the intense upward motion. At a particular phase, the new cells merged with the updraft of the gravity waves, leading to an intense updraft that strengthened the squall line.

关键词： squall line structural feature gravity wave cold pool outflow

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Evaluation of Two Momentum Control Variable Schemes and Their Impact on the Variational Assimilation of Radar Wind Data:Case Study of a squall line

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Advances in Atmospheric Sciences 2016年第10期33卷 1143-1157页

作者： Xin LI Mingjian ZENG Yuan WANG Wenlan WANG Haiying WU Haixia MEI Jiangsu Research Institute of Meteorological Sciences Nanjing 210009China Key Laboratory of Mesoscale Severe Weather/MOE and School of Atmospheric SciencesNanjing UniversityNanjing 210023China Jiangsu Provincial Observatory Nanjing 210008China

Different choices of control variables in variational assimilation can bring about different influences on the analyzed atmospheric state. Based on the WRF model＇s three-dimensional variational assimilation system, this study compares the be- havior of two momentum control variable options-streamfunction velocity potential （ψ-χ） and horizontal wind components （U-V）-in radar wind data assimilation for a squall line case that occurred in Jiangsu Province on 24 August 2014. The wind increment from the single observation test shows that the ψ-χ control variable scheme produces negative increments in the neighborhood around the observation point because streamfunction and velocity potential preserve integrals of velocity. On the contrary, the U-V control variable scheme objectively reflects the information of the observation itself. Furthermore, radial velocity data from 17 Doppler radars in eastern China are assimilated. As compared to the impact of conventional observation, the assimilation of radar radial velocity based on the U-V control variable scheme significantly improves the mesoscale dynamic field in the initial condition. The enhanced low-level jet stream, water vapor convergence and low-level wind shear result in better squall line forecasting. However, the ψ-χ control variable scheme generates a discontinuous wind field and unrealistic convergence/divergence in the analyzed field, which lead to a degraded precipitation forecast.

关键词： three-dimensional variational assimilation momentum control variable Doppler radar data squall line

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THE RELATIONSHIP BETWEEN HORIZONTAL VORTICITY INDUCED BY VERTICAL SHEAR AND VERTICAL MOTION DURING A squall line PROCESS

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Journal of Tropical Meteorology 2018年第1期24卷 1-14页

作者： ZHAO Xiang-jun DING Zhi-ying Nanjing University of Information Science and Technology/Key Laboratory of Meteorological Disaster co-fimded by Ministry of Education and Jiangsu Province Jiangsu Nanjing 210044 China State Key Laboratory of Severe Weather Chinese Academy of Meteorological of Sciences Beijing 100081 China

The horizontal vorticity equation used in this study was obtained using the equations of motion in the pressure coordinate system without considering friction, to reveal its relationship with vertical shear. By diagnostically analyzing each term in the horizontal vorticity equation during a squall line process that occurred on 19 June 2010, we found that the non-thermal wind term had a negative contribution to the local change of upward movement in the low-level atmosphere, and that its impact changed gradually from negative to positive with altitude, which could influence upward movement in the mid-and upper-level atmosphere greatly. The contribution of upward vertical transport to vertical movement was the largest in the low-level atmosphere, but had negative contribution to the upper-level atmosphere. These features were most evident in the development stage of the squall line. Based on analysis of convection cells along a squall line, we found that in the process of cell development diabatic heating caused the subsidence of constant potential temperature surface and non-geostrophic motion, which then triggered strong convergence of horizontal acceleration in the mid-level atmosphere and divergence of horizontal acceleration in the upper-level atmosphere. These changes of horizontal wind field could cause a counterclockwise increment of the horizontal vorticity around the warm cell, which then generated an increase of upward movement. This was the main reason why the non-thermal wind term had the largest contribution to the strengthening of upward movement in the mid-and upper-level atmosphere. The vertical transport of large value of horizontal vorticity was the key to trigger convection in this squall line process.

关键词： horizontal vorticity horizontal vorticity equation vorticity of horizontal vorticity squall line non-thermal wind

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A Modeling Study on the Mechanism of Convective Initiation of a squall line over Northeastern China

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Journal of Tropical Meteorology 2020年第3期26卷 336-347页

作者： ZHANG Zhe ZHOU Yu-shu DENG Guo Key Laboratory of Water Cycle and Related Land Surface Processes Institute of Geographic Sciences and Natural Resources ResearchChinese Academy of SciencesBeijing 100101 China Key Laboratory of Cloud-Precipitation Physics and Severe Storms Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029 China National Meteorological Center Beijing 100081 China

High-resolution numerical simulation results of a squall line initiated along a convergence zone in northeast China on 26 June 2014 were presented in this *** simulation was performed by a convection-permitting model with coarse and fine grids of 4 and 1.33 km,respectively,and the simulation results were validated against the *** showed that the simulation adequately reproduced the life cycle of the squall line,which allowed detailed investigation of the mechanism of convective initiation in this *** synoptic condition was favorable for convective initiation and the convection was triggered in a convergence zone,where a branch of dry and cold air and a branch of moist and warm air *** water vapor flux divergence was inhomogeneous and some cores of water vapor convergence existed in the convergence *** cores were the spots where water vapor converged intensely and the air there was forced to rise,creating favorable spots where the convection was initially triggered.A series of quasi-equally spaced vortices near the surface,which themselves were the result of horizontal shear instability,were accountable for the inhomogeneity of the surface water vapor flux *** vortices rotated the moist air into their north and dry air into their south,thus creating more favorable spots for convective initiation in their *** initiation,the updraft turned the horizontal vorticity into vertical vorticity in the *** vortices near the surface collaborated with the vorticity maxima in the mid-level and enhanced the development of convection by providing water vapor.

关键词： squall line convective initiation vortices

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