Analysis on development mechanism of two consecutive warm zone squall lines in Zhejiang Province

doi:10.11755/j.issn.1006-7639(2023)-05-0764

Abstract

Abstract:

Two consecutive squall lines affected Zhejiang Province on 25 April 2022, causing a large-range wind disaster. The study of the occurrence and development of continuous squall lines is of important reference value for the forecast of such catastrophic weather. The development process and mechanism of two consecutive squall lines are analyzed by using ERA5 reanalysis data, observations of surface automatic meteorological stations, blackbody brightness temperature (TBB) and doppler radar data. The results show that the two consecutive squall lines (named “squall line 1” and “squall line 2”, according to the sequence of squall lines) developed in the upper jet stream divergence area, in front of the middle-level trough and in the warm zone in the south side of the low vortex at the lower level and at the top of the southwest jet stream axis. The squall line 1 was a medium β scale squall line triggered by the upper dry intrusion and the weak cold front near the surface in the early stage. The meso-scale convergence line caused by the bottom outflow and the strong inflow of southeast wind over the Hangzhou Bay and the vertical wind shear at the lower level promoted the squall line to strengthen gradually during its movement. The squall line 2 rose from the middle β scale to the middle α scale during the primary to mature stage. It was related to the migration of the upstream convective system in the early stage. Its formation was related to the migration of the upstream convective system in the early stage, affected by the upper dry intrusion, the vertical wind shear at the lower level, the convergence line of the weak cold front behind the squall line 1 and the merging of the upstream echoes, the upscaling phenomenon occurred in the mature stage. When the vertical wind shear decreased and the northern segment of the squall line 2 moved into the sea faster, the squall line 2 broke.

Key words: squall line, upscale growing, isentropic potential vortex, weak cold front, vertical wind shear

摘要：

2022年4月25日连续两次飑线影响浙江且造成大范围风灾，研究连续飑线的发生发展对此类灾害性天气预报有重要参考价值。应用ERA5再分析资料、地面自动气象站实况数据、云顶亮温资料和多普勒雷达数据，分析连续飑线发展过程及机制。结果表明：连续两次飑线（按照飑线发生先后顺序分别称“飑线1”和“飑线2”）是在高层急流辐散区内、中层槽前、低层低涡南侧和西南急流轴顶端的暖区中发展起来的。飑线1为中β尺度飑线，初生阶段受高层干侵入和近地面弱冷锋触发，底部出流与杭州湾东南风强入流造成的中尺度辐合线和低层垂直风切变促使其移动过程中逐渐增强；飑线2初生到成熟阶段从中β尺度升至中α尺度，其初生与上游对流系统移入有关，受高层干侵入、低层垂直风切变、飑线1后部弱冷锋辐合线和上游回波并入影响，成熟阶段出现升尺度增长现象，当垂直风切变减小，且飑线2北段入海移速加快后，飑线2出现断裂。

关键词: 飑线, 升尺度增长, 等熵位涡, 弱冷锋, 垂直风切变

CLC Number:

P458

QIAN Zhuolei, ZHAO Chiyu, ZHU Zhejun, SHENG Zhewen. Analysis on development mechanism of two consecutive warm zone squall lines in Zhejiang Province[J]. Journal of Arid Meteorology, 2023, 41(5): 764-773.

钱卓蕾, 赵驰宇, 朱哲君, 沈哲文. 浙江连续两次暖区飑线发展机制分析[J]. 干旱气象, 2023, 41(5): 764-773.

Figures/Tables 9

Fig.1 The evolution of combined reflectivity factor at Jinhua station （the top， Unit： dBZ） and TBB （the bottom， Unit： ℃） on 25 April 2022

Fig.2 The 200 hPa wind field （wind vectors， Unit： m·s-1）（a）， 500 hPa geopotential height field （contours， Unti： gpm） and 850 hPa wind field （wind vectors， Unit： m·s-1）（b） at 12：00 on 25 April 2022

Fig.3 The sounding curves at Jiaxing station at 11：00 （a） and Shaoxing station at 14：00 （b） on 25 April 2022 （The red thick line is the stratification curve， and the dark green thick line is the dew point curve， and the vertical wind field is shown on the right）

Fig.4 Distribution of convective effective potential energy （color shaded， Unit： J·kg-1）， K index （brown solid lines， Unit： °C） and temperature difference between 850 hPa and 500 hPa （blue dotted lines， Unit： °C） at 12：00 （a）， 14：00 （b）， 16：00 （c） and 18：00 （d） on 25 April 2022

Fig.5 The vertical section of vortex potential （isolines， Unit： 10-6 m2·s-1·K·kg-1）， relative humidity （color shaded， Unit： %） and wind field （wind vectors， Unit： m·s-1） on the isentropic surface at 12：00 （a）， 14：00 （b）， 16：00 （c） and 18：00 （d） on 25 April 2022

Fig.6 The one-hour surface extremely strong wind （wind vectors， Unit： m·s-1）， one-hour pressure change （isolines， Unit： hPa） and radar reflectivity factor on 0.5° elevation at Jinhua station （color shaded， Unit： dBZ） at 13：00 （a）， 15：00 （b）， 17：00 （c） and 19：00 （d） on 25 April 2022 （The red thick dashed line represents the mesoscale convergence line）

Fig.7 Vertical wind shear from 0 to 3 km （wind vectors， Unit： m·s-1）， one-hour ground temperature change （isolines， Unit： °C） and radar reflectivity factor （color shaded， Unit： dBZ） on 0.5° elevation at Jinhua station at 13：00 （a）， 15：00 （b）， 17：00 （c）， 19：00 （d） on 25 April 2022

Fig.8 Vertical profiles of reflectivity factor along vertical direction of the squall line （the AB and CD segments in fig.7） at 15：00 （a） and 17：00 （b） on 25 April 2022 （Unit： dBZ）

Fig.9 Schematic diagram of the development of two consecutive squall lines

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