Evolution Process and Mechanism Analysis of the Mesoscale System of an Extreme Summer Rainstorm in Shandong Province
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摘要: 对2020年7月22日山东半岛一次极端暴雨天气过程开展观测分析,并利用中尺度模式WRF对此次局地降水过程进行了高分辨率数值模拟,对暴雨过程进行了天气背景和中尺度降雨的诊断。WRF模式较好地再现了此次极端暴雨过程,结果表明:此次极端暴雨过程短时降水强度大且局地性强,在时空上具有明显中尺度特征。降水发生在北抬副热带高压与华北低涡底部之间的西南气流中,强低涡与低空急流是影响此次降水的重要天气系统。西南急流为本次暴雨过程极端水汽的主要输送载体;在弱高空辐散场下,从地表延伸至500 hPa高空的深厚低涡是造成本次暴雨的主要影响因子,其时空演变特征与中尺度云团变化一致,与暴雨的发生直接相关。低涡、低空急流和副高之间的相互作用使低涡加强发展,低涡南部有暖湿气流入流,北部有干冷气流流入,比湿梯度基本呈现为自南向北递减分布,是典型的伴有低空急流的中尺度低涡流场分布;低涡辐合及其与副热带高压边缘强风速带的共同作用,导致强垂直运动发展并维持,是造成本次山东半岛极端暴雨的重要原因。Abstract: The synoptic circulation pattern and mesoscale systems associated with the extreme torrential rain occurring in the Shandong Peninsula on 22 July 2020, are analyzed with conventional observational data and a high-resolution numerical simulation using the mesoscale model WRF. The simulation agreed well with the precipitation process. The results show that the rainstorm process is characterized by mesoscale features spatially and temporally, represented in its high intensity of short-term rainfall, severe locality, etc. Precipitation occurs in the southwest airflow between the subtropical north elevation and the bottom of a low vortex. Strong vortices and low-level jets are important weather systems that affect this precipitation. The southwest jet stream is the main carrier of extreme water vapor during this heavy precipitation. Under a high-level weak divergent field, the main influence of this rainstorm is the deep low vortex extending from the surface to the 500-hPa high altitude. Its temporal and spatial evolution characteristics are consistent with the mesoscale cloud cluster changes shown by the FY-2E hourly TBB data. This consistency is directly related to the occurrence of heavy rain. The interaction between the vortex, low-level jet, and subtropical high strengthens the development of the low vortex. There are warm, wet airflows from the north and cold, dry airflows from the south of the low vortex. The specific humidity gradient is roughly distributed from south to north, which is a typical flow field distribution of a vortex accompanied by a low-level jet. The convergence of the low vortex and its interaction with the strong wind speed belt at the edge of the subtropical high lead to the development and maintenance of strong vertical motion, thereby contributing to the persistence of extreme rainstorms.
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Key words:
- Shandong Peninsula /
- Extreme rainstorm /
- Low vortex /
- Low-level jet /
- Developmental process
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图 2 2020年7月22日00时(左)、12时(右)位势高度(黑色实线,单位:dagpm)、风场(箭头,单位:m s−1)分布:(a、b)850 hPa;(c、d)500 hPa;(e、f)200 hPa。阴影为大于3500 m地形
Figure 2. Distributions of geopotential height (black solid lines, units: dagpm) and wind (vectors, units: m s−1) at 0000 UTC (left) and 1200 UTC (right) on 22 July 2020: (a, b) 850 hPa; (c, d) 500 hPa; (e, f) 200 hPa. The gray shading is the terrain larger than 3500 m
图 3 2020年7月(a)22日18时、(b)23日00时850 hPa位势高度(黑色实线,单位:dagpm)、温度(红色虚线,单位:°C)、大于1.5 m s−1的风场(黑色箭头)、相对涡度(彩色阴影,单位:10−4 s−1)。灰色阴影表示地形(单位:m)
Figure 3. Distributions of geopotential height (black solid lines, units: dagpm), temperature (red dashed lines, units: °C), wind more than 1.5 m s−1 (black vectors), relative vorticity (color shadings, units: 10−4 s−1) at 850 hPa at (a) 1800 UTC and (b) 2300 UTC on 22 July 2020. The gray shading shows the terrain (units: m)
图 4 2020年7月(a)22日18时、(b)23日00时850 hPa水汽通量(黑色流线)、水汽通量散度(彩色阴影,单位:10−8 kg m−1 s−1 hPa−1)。灰色阴影表示地形(单位:m)
Figure 4. Moisture fluxes (black streamline) and their divergence (color shadings, units: 10−8 kg m−1 s−1 hPa−1) at 850 hPa at (a) 1800 UTC and (b) 2300 UTC on 22 July 2020. The gray shading shows the terrain (units: m)
图 6 2020年7月22日04时至23日00时850 hPa位势高度(黑色实线,单位:dagpm)和TBB逐小时分布(彩色阴影,单位:°C)。灰色阴影表示地形高度(单位:m)
Figure 6. Hourly distributions of geopotential height (black solid lines, units: dagpm) and brightness temperature (color shadings, units: °C) from the FY-2E satellite at 850 hPa from 0400 UTC 22 July to 0000 UTC 23 July 2020. The gray shading shows the terrain (units: m)
图 8 2020年7月22日实况(左)、模拟(右)的6 h累计降水量(单位:mm):(a、b)00~06时;(c、d)06~12时;(e、f)12~18时;(g、h)18时至23日00时
Figure 8. Accumulated 6-h precipitation (units: mm) obtained from simulation (left) and observation (right): (a, b) 0000–0600 UTC 22 July 2020; (c, d) 0600–1200 UTC 22 July 2020; (e, f) 1200–1800 UTC 22 July 2020; (g, h) 1800 UTC 22 July 2020 to 0000 UTC 23 July 2020
图 9 2020年7月22日山东省青岛探空站(a、b)00时、(c、d)12时实测(左)、模拟(右)探空曲线。绿色粗实线表示露点温度,红色粗实线表示层结曲线
Figure 9. Soundings obtained from (a, c) observation (left), (b, d) simulation (right) at Qingdao station in Shandong Province at (a, b) 0000 UTC and (c, d) 1200 UTC 22 July 2020. The bold green line is the dew point temperature, and the bold red line is the stratification curve
图 12 2020年7月22日经低涡中心(图10a黑色线段所示位置)的相对涡度垂直剖面(彩色阴影,单位:10−5 s−1):(a)00时;(b)04时;(c)14时;(d)18时。灰色阴影为地形,红色三角表示近地面低涡中心,下同
Figure 12. Vertical cross sections of the relative vorticity (color shadings, units: 10−5 s−1) across the low-vortex center (black line in Fig. 10a) on 22 July 2020: (a) 0000 UTC; (b) 0400 UTC; (c) 1400 UTC; (d) 1800 UTC. The gray shading indicates the terrain, and the red triangle indicates the low-vortex center in the surface layer, the same below
图 13 2020年7月22日经低涡中心(图10a黑色线段所示位置)的垂直速度(阴影,单位:10−5 m s−1)、风矢量(箭头,单位:m s−1)的垂直剖面:(a)00时;(b)10时;(c)13时;(d)17时
Figure 13. Vertical cross sections of the vertical velocity (color shadings, units: 10−5 m s−1) and wind vector (arrows, units: m s−1) across the low-vortex center (black line in Fig. 10a) on 22 July 2020: (a) 0000 UTC; (b) 1000 UTC; (c) 1300 UTC; (d) 1700 UTC
图 15 2020年7月22日经低涡中心沿线(图14a红色线段)温度扰动(彩色阴影,单位:°C)、温度(红色实线,单位:°C)、相当位温(蓝色实线,单位:K)的垂直剖面:(a)03时;(b)07时;(c)18时;(d)22时
Figure 15. Vertical cross sections of temperature perturbation (color shadings, units: °C), temperature (red solid lines, units: °C), and equivalent potential temperature (blue solid lines, units: K) across the low-vortex center (red line in Fig.14a) on 22 July 2020: (a) 0300 UTC ; (b) 0700 UTC; (c) 1800 UTC; (d) 2200 UTC
图 16 2020年7月22日经低涡中心沿线(图10a黑色线段)相对湿度(彩色阴影)、比湿(蓝色实线,单位:g kg−1)、风矢量(箭头,单位:m s−1)的垂直剖面:(a)00时;(b)05时;(c)14时;(d)22时
Figure 16. Vertical cross sections of the relative humidity (color shadings), specific humidity (blue solid lines, units: g kg−1), and wind (arrows, units: m s−1) across the low-vortex center (black line in Fig.10a) on 22 July 2020: (a) 0000 UTC; (b) 0500 UTC; (c) 1400 UTC; (d) 2200 UTC
表 1 WRF模式模拟中使用的主要参数
Table 1. List of main parameters used in WRF (Weather Research and Forecasting) simulation
模拟区域一 模拟区域二 模拟区域分辨率 15000 m 3000 m 格点数 155×130 571×521 微物理方案 Thompson Graupel Scheme (Thompson et al., 2008) Thompson Graupel Scheme (Thompson et al., 2008) 对流参数化方案 Grell 3D Ensemble Scheme (Grell and Dévényi, 2002) Grell 3D Ensemble Scheme (Grell and Dévényi, 2002) 长波辐射方案 RRTMG Scheme (Iacono et al., 2008) RRTMG Scheme (Iacono et al.,2008) 短波辐射方案 RRTMG Scheme (Mlawer et al., 1997) RRTMG Scheme (Mlawer et al., 1997) 近地表方案 Monin-Obukhov (Janjic Eta) Similarity Scheme
(Monin and Obukhov, 1954; Janjic, 1996)Monin-Obukhov (Janjic Eta) Similarity Scheme
(Monin and Obukhov, 1954; Janjic, 1996)陆地过程方案 Noah Land–Surface Model (Chen and Dudhia, 2001) Noah Land–Surface Model (Chen and Dudhia, 2001) -
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