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Meso-scale Convective Characteristics of "7·22" Extreme Rain in the West Mountainous Area of Fujian
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摘要: 2015年7月22日福建西部山区经历了一次罕见的极端降水过程，6 h降水量高达254.9 mm，24 h最大降水量达295.5 mm。利用常规天气资料、自动气象站、卫星云图、风廓线雷达以及多普勒天气雷达资料，分析此次过程的中尺度对流系统的环境条件及结构演变特征。分析表明：低空季风槽北抬减弱后的切变和高空高压之间的南北向槽缓慢向东北移动是此次强降雨的主要影响系统，不稳定能量加大、抬升凝结高度和自由对流高度低、大气可降水量大及中等到弱的垂直风切变形成有利于中尺度对流系统发展的环境条件。中尺度对流系统在发展过程中结构发生改变，由线状对流伴随层云（TL/AS）的结构转变为静止后向建立的中尺度对流系统，极端降水出现在静止后向传播阶段。高空冷空气入侵，低空西南急流加强并伴风速辐合，冷暖空气交汇导致中尺度对流系统加强发展，边界层西南气流在有利的喇叭口地形作用下加强抬升，北上受到山脉阻挡形成小涡旋，西北侧对流单体移入后不断加强，对流单体的移动方向和传播方向相反，中尺度对流系统形成静止后向传播，产生列车效应，出现极端降水。Abstract: An extreme severe rain occurred in the west mountainous area of Fujian on 22 July 2015, with the precipitation of 254.9 mm for 6 hours and the maximum total precipitation of 295.5 mm. Using conventional observations, automatic weather station data, satellite data, wind-profiling radar and CINRAD-SA Doppler radar data, this extreme severe precipitation is analyzed focusing on the environmental conditions and structure characteristics of the meso-scale convective system (MCS). Results show that predominate influencing systems are the low-level shear line and the upper trough between subtropical high and the anticyclone over Yunnan and Guangxi. The reinforcement of unsteady convective stratification, decrease in the level of lifting condensation and free convection, high atmospheric precipitable water and weak vertical wind shear over the rainstorm-hit area are all favorable to the development of MCS. The initial convective cloud develops on the edge of Guangdong and Fujian. Convective cells develop strongly with the favorable meso-scale environmental conditions. At the stage of northeast development, convective cells are born in the north of MCS and move southeast. Many northwest and southeast short echo bands come into being one after another. MCS moves northeastward under actions of cell advection and storm propagation. At the stage of quasi-stationary, the strong temperature gradient area locates in the middle of MCS. The north and south cloud clusters weaken rapidly. The structure of MCS changes from training line and adjoining stratiform MCS to back-building and quasi-stationary MCS in the stage of development. Back-building and quasi-stationary MCS results in the extreme severe rain. The northwest airflow on high level increases and extends to low level. The inflow in front of MCS on low level is strengthened and extends to high level. The cold air intrusion at high level and reinforcement of southwest jet with wind velocity convergence at low level over the rainstorm-hit area lead to the development of MCS. The effect of the trumpet-shaped topography strengthens the southwest airflow on the boundary layer. A small cyclonic eddy generates in the north of Liancheng and is closely related to the southwest airflow within the boundary layer blocked by mountain. When the northwest convective cell moves in, the convective cell strongly develops. The northeast-southwest back-propagating MCS rarely moves because directions of cell advection and storm propagation are in confrontation. The back-propagating MCS causes obvious train effect, which brings about extreme severe rain.
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Key words:
- extreme severe rain;
- MCS;
- quasi-stationary back-propagating
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图 1 2015年7月21日20：00—22日20：00龙岩降水量分布(单位：mm)
Fig. 1 Observed precipitation at Longyan from 2000 BT 21 Jul to 2000 BT 22 Jul in 2015(unit:mm)
图 2 2015年21日20：00—22日20：00连城、培田及文亨3站小时降水量柱形图
Fig. 2 Hourly precipitation at Liancheng, Peitian and Wenheng from 2000 BT 21 Jul to 2000 BT 22 Jul in 2015
图 3 2015年7月21—22日中尺度对流系统龙岩雷达组合反射率因子演变(黑色圆圈代表强中心)
Fig. 3 Evolution of MCS in the composite reflectivity of Longyan radar from 21 Jul to 22 Jul in 2015
图 4 2015年7月22日01:33，02:03和02:34龙岩雷达0.5°仰角反射率因子(填色)
(02：03和02：34叠加02:00和03:00降水量(数字)，单位：mm)
Fig. 4 The reflectivity(the shaded) of Longyan radar with 0.5° elevation at 0133 BT, 0203 BT and 0234 BT 22 Jul 2015
(0203 BT and 0234 BT superpose 0200 BT, 0300 BT hourly precipitation(the number), unit:mm)
图 5 2015年7月22日09:54龙岩雷达组合反射率因子(a)、2.4°(b)及3.4°(c)仰角径向速度
Fig. 5 Composite reflectivity(a) and velocity of Longyan radar with the elevation of 2.4°(b), 3.4°(c) at 0954 BT 22 Jul 2015
图 6 2015年7月22日01：36—03：18武平风廓线雷达风场随高度变化
Fig. 6 Wind vector of Wuping wind-profiling radar from 0136 BT to 0318 BT on 22 Jul 2015
图 7 2015年7月22日09:00连城地面风场
(填色为地形)
Fig. 7 Surface wind field of Liancheng at 0900 BT 22 Jul 2015
(the shaded denotes terrain)
表 1 2015年7月21—22日赣县、河源和厦门探空站环境参数
Table 1 Enviromental parameters of Ganxian, Heyuan and Xiamen from 21 Jul to 22 Jul in 2015
时间 站点 对流有效位能/(J·kg-1) 对流抑制能量/(J·kg-1) 抬升凝结高度/hPa 自由对流高度/hPa 地面到500 hPa垂直风切变/(m·s-1) 21T08:00 赣县 318.9 18.3 963.3 791.3 5.55 河源 27.9 1.4 988.7 962.7 5.46 厦门 2130.8 3.0 972.0 952.0 13.96 21T20:00 赣县 655.7 50.0 947.1 817.1 7.03 河源 425.3 9.2 983.5 897.5 10.60 厦门 1340.3 3.3 973.8 947.8 11.10 22T08：00 赣县 501.8 38.5 946.2 808.2 6.00 河源 603.2 8.2 976.9 926.9 4.51 厦门 923.9 1.6 981.9 957.9 6.02 
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