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“7·18”济南突发性大暴雨特征
A Jinan Heavy Rainfall on 18 July 2007
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摘要: 运用FY-2号气象卫星资料、NCEP再分析资料、常规资料以及自动站加密观测资料，对2007年7月18日济南市突发性大暴雨天气过程的形成发展进行了综合分析。结果显示：这次大暴雨发生在大气层结十分不稳定和高、低空急流耦合的有利大尺度环流背景下，由强烈发展的中尺度对流云团直接造成，具有明显的中尺度特征。低层冷空气南侵，触发了具有高不稳定能量的对流发展；低空强劲的西南急流直抵黄河下游一带，不仅与南下的冷空气形成强烈辐合，还将大量水汽和能量输送到该地区，使降水得以加强。Abstract: Jinan is stricken suddenly by an extraordinary rainstorm on 18 July 2007. From 17:30 to 20:30, the maximum rainfall of the city exceeds 153.1 mm. An synthetic analysis of this heavy rain event is performed, using multiple data, including FY-2 double satellite data, NCEP 6-hour reanalysis data, routine observational data and automatic meteorological station data. The results show the heavy rainfall takes place under the favorable large-scale circumfluence, which includes the continental high pressure in west China developing eastward, and Jinan locates at the northeast of it. At the same time, coupling between a high level jet steam and a low level jet steam intensifies, and becomes strong divergence in the upper and strong convergence in the low over Jinan. The cold vortex in northeast China develops dramatically, and the cold air of its rear strengthens. The short wave trough at middle layer moves eastward, and lies over the shear-line in the low level. Both of them form the shape of forward trough. All of these lead together to atmospheric stratification around Jinan turning very unstable. This rainfall process is caused directly by strong meso-scale convective cloud, which is formed by the mergence of two deeply convective clusters at the tail of frontal clouds, and it shows a quasi-round shape structure of a horizontal scale of 200 km×200 km, and a time scale of no more than 5 hours. There is a meso-scale low pressure over the surface corresponding to the cloud. The heavy rain occurs during the rapid intensification stage of the meso-seale convective system. In addition, the transport of warm and moist southwest air current in the low-level leads heavy rain to develop strongly. This water channel extends northeastward and shows northeast-southwest orientation via Jinan, which provides plenty of water for rainfall.
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Key words:
- abrupt heavy rain;
- strong convective cloud;
- jet stream;
- cold air
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图 1 2007年7月18日14:00 500 hPa位势高度场 (单位:dagpm) 和850 hPa风矢量场
(粗实线为500 hPa槽线，粗虚线为850 hPa切变线; 黑色圆点为济南市, 下同)
Fig. 1 The geopotential height of 500 hPa (unit：dagpm) and wind field of 850 hPa at 14：00 on July 18, 2007
(solid line is for the rough, dashed line is for the shear; black dot is Jinan, hereinafter)
图 3 2007年7月18日13:00—21:00 FY-2C卫星 BB分布图
(单位: ℃;阴影为TBB低于-32℃)
Fig. 3 The infrared brightness temperature of FY-2C during 13:00-21 :00 on July 18, 2007
(unit: ℃; shaded areas denote infrared brightness temperature below -32℃)
图 4 2007年7月18日08:00—19日07:00济南市每小时降雨量和FY-2C逐时TBB变化
Fig. 4 The change of ihe hourly precipitation and FY-2C hourly TBB from 08：00 on July 18 to 07：00 on July 19, 2007
图 5 2007年7月18日14:00沿117°E的θse经向垂直剖曲图 (单位: K; ▲为济南市）
Fig. 5 Meridian-height section of θse along 117.0°E at 14:00 on July 18, 2007(unit: K; ▲ is Jinan)
图 6 2007年7月18日14:00地面流场 (a) 和17:00地面气压场 (b) (Unit: hPa)
Fig. 6 The surface stream field at 14:00 and the surface pressure field at 17:00 on July 18, 2007 (unit：hPa)
图 7 2007年7月18日14:00 925 hPaa 24 h 变温场 (单位: ℃)
Fig. 7 The 24-hour change temperature field of 925 hPa at 14:00 on July 18, 2007 (unit: ℃)
图 8 2007年7月18日14:00 1000~400 hPa水汽通量散度场
(单位：10-4g/(s·hPa·cm2), 虚线为最大水汽通量散度轴）
Fig. 8 The divergence of water flux integrated from bottom to 400 hPa at 14:00 on July 18, 2007
(unit：10-4g/(s·hPa·cm2), dashed line indicates the maximum axis of water flux divergence)
表 1 2007年7月18日暴雨发生前后不稳定能呈的比较
Table 1 The comparison of instability energy between the pre-past rainstorm on July 18, 2007
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