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Statistical Characteristics of Isolated Convection in the Jianghuai Region
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摘要: 孤立对流云是江淮地区重要的降水云系，通过分析江淮地区2013—2016年6—9月的多普勒天气雷达数据，统计得到664个对流云，其中孤立对流云196个，占江淮地区对流云发生频率的29.5%，7月和8月是江淮地区孤立对流云的高发期，6月相对较少，9月最少，同时12：00（北京时，下同）—18：00是孤立对流云的高发时段，05：00—07：00孤立对流云发生频率最低。针对2013年7月20日安徽定远出现的孤立对流云个例，综合分析多普勒天气雷达和C波段连续波雷达探测资料，发现此次暖区孤立对流云内部强反射率因子中心交替生成，导致内部反射率因子呈强弱交替出现的波状结构，沿着移动方向由弱到强，降水粒子下落速度与之对应，降水粒子最大落速出现在孤立对流云中下部的强反射率因子区域，速度超过10 m·s-1。Abstract: Isolated convective clouds are important precipitation cloud systems in the Jianghuai Region. Based on the analysis of radar data from June to September during 2013-2016, a total of 664 convective clouds are identified, in which 196 are isolated convective clouds. It is found that isolated convective clouds account for 29.5% of the total convective clouds in the Jianghuai Region. July and August are the high incidence periods of isolated convective clouds, while isolated convective clouds occur less in June and the frequency of occurrence is the least in September. At the same time, the high incidence time of isolated convective clouds is from 1200 BT to 1800 BT, and the lowest incidence time is from 0500 BT to 0700 BT. It is found that the circulation background has a great influence on the isolated convective clouds in this area. July-August is the high incidence of isolated convective clouds in the Jianghuai Region, which is mainly related to the circulation background during this period. The Jianghuai Region is often in the periphery of the subtropical anticyclone in July-August due to the high temperature and the increase of local unstable energy, and it often leads to the occurrence of local scattered convective clouds. In addition, in view of the isolated convective clouds at Dingyuan, Anhui Province on 20 July 2013, the Doppler radar and the C-band Frequency Modulation Continuous Wave radar detection data are comprehensively analyzed. It is found that there is a strong echo center alternately generated in the isolated convective clouds in the warm area, resulting in the wave structure of the internal echo reflectivity with the intensity distribution from weak to strong along the moving direction. In the vertical direction, the radar reflectivity factor increases at first and then decreases from top to bottom. The falling velocity intensity of precipitation particles correspond to it. The maximum falling velocity of precipitation particles appears in the strong echo region in the middle and lower parts of isolated convective clouds, and the velocity is over 10 m·s-1.
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图 1 雷达位置及研究区域
(×为多普勒天气雷达位置，Δ为C波段连续波雷达位置)
Fig. 1 The location of radars and the target area
(× is the location of Doppler radar, Δ is the location of C-FMCW)
图 2 2013—2016年6—9月江淮地区孤立对流云发生频次
Fig. 2 The frequency of isolated convective clouds in the Jianghuai Region from Jun to Sep during 2013-2016
图 3 2013年7月31日08:00 500 hPa高度场(等值线，单位：gpm)和850 hPa风场(风羽)
Fig. 3 500 hPa height (the contour, unit:gpm) and 850 hPa wind (the barb) at 0800 BT 31 Jul 2013
图 4 2013年7月20日08:00 500 hPa高度场(等值线，单位：gpm)和850 hPa风场(风羽)
Fig. 4 500 hPa height (the contour, unit:gpm) and 850 hPa wind (the barb) at 0800 BT 20 Jul 2013
图 5 2013年7月20日10:00—13:00定远站降水量
Fig. 5 Rainfall amount at Dingyun Station from 1000 BT to 1300 BT on 20 Jul 2013
图 7 2013年7月20日定远站组合反射率因子
Fig. 7 Superimposition of radar reflectivity at Dingyuan Station on 20 Jul 2013
图 8 2013年7月20日定远孤立对流云垂直结构(a)反射率因子, (b)粒子下落速度
Fig. 8 Vertical structure of an isolated convection at Dingyuan Station on 20 Jul 2013 (a)reflectivity, (b)particle fall velocity
表 1 C波段连续波雷达和多普勒天气雷达主要参数
Table 1 Main parameters of C-FMCW radar and Doppler radar
雷达参数 多谱勒天气雷达 C波段连续波雷达 探测方式 体扫描方式 固定式垂直指向 探测量程 水平460 km，垂直20 km 150 m~24 km 时间分辨率 6 min 3 s 空间分辨率 1 km 30 m 探测精度 ≤1 dBZ ≤1 dBZ 
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表 2 2013—2016年6—9月不同对流云数量统计
Table 2 The number of different convections from Jun to Sep during 2013-2016
月份 孤立对流云数量 对流云数量 孤立对流云所占比例 6 30 157 19.1% 7 53 196 27% 8 89 228 39% 9 24 83 28.9%
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