Observational Analysis of Mesoscale Rain Cluster During Typical Torrential Rain Processes in Inner Mongolia
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摘要: 利用FY-2E逐时云顶黑体亮温资料 (TBB)、闪电定位资料、自动气象站资料和逐时降水资料,对2009—2013年6—8月内蒙古7例暴雨天气过程的中尺度雨团特征进行分析。结果表明:内蒙古暴雨的降水强度在1~3 h即可达到暴雨或大暴雨量级,中尺度雨团活动是内蒙古暴雨过程形成原因,而80%雨团活动是中尺度对流系统 (MCS) 造成的。MCS内TBB不超过-52℃冷云区和地闪密度大值中心对雨团强度和发展具有重要的指示作用,冷锋云系中MCS造成的雨团多原地生成和消亡,TBB不超过-52℃冷云区面积小,维持时间为2~8 h,地闪密度增长缓慢而且发生频次低;冷涡云系中雨团跳跃式出现在MCS冷云区或冷空气流入一侧,出现TBB不超过-62℃冷云区,雨团出现频次高,持续出现时间可长达24 h,地闪密度增长迅速且发生频次高。7次暴雨过程中约有60%雨团伴有地闪活动,地闪密度达到最大值时刻预示未来1~3 h最强雨团出现和MCS发展到成熟。地面加密风场中尺度辐合线先于MCS和雨团出现,中尺度辐合线造成的局地辐合可作为MCS发展的启动机制。Abstract: Inner Mongolia Autonomous Region is located in the northern frontier of China, where characteristics of torrential rain are local and convective, and the strong precipitation duration is short. High temporal and spatial data such as the satellite cloud, lighting data and automatic weather station data are very effective tools for discovering and monitoring mesoscale convective sgstem (MCS) continuously. But these approaches are not often carried out in Inner Mongolia. In view of this, using black body temperature (TBB) data of FY-2E, lightning data, automatic weather station data and hourly precipitation data, characteristics of mesoscale rain cluster (RC) of seven typical torrential rain cases are studied in Inner Mongolia from June to August during 2009-2013. Results show that in Inner Mongolia, hourly rain intensity of torrential rain processes can reach torrential rain or heavy torrential rain in 1 h or 3 h, and 80% RC activity is caused by MCS. The strong precipitation is closely related with the terrain, and the highest value occurs in the southward mountain facing warm moist airflow, which are favorable for the development of MCS. The highest peak of strong precipitation occurs in the afternoon, and the secondary peak occurs in the midnight and early morning. It has important presage function with regard to intensity and development of RC that the TBB no more than-52℃ cold-cloud shield centroid of MCS and high value center of cloud-to-ground lightning flashes density (CGD). RC in MCS of cold front cloud system gives expression to generation and extinction in the same region, the TBB no more than-52℃ cold-cloud shield centroid is small and last for 2-8 h, CGD increases slowly and has lower frequency. RC occurs jumpily in cold cloud area or the side cold air flowing into in MCS of the vortex clouds system, the TBB no more than-62℃ cold-cloud shield centroid emerge and last for 24 h, CGD increases rapidly and occur with higher frequency. RC is located in right side of coldest cloud of forward MCS where the cold air flows into. But the region where MCS shifts out exist RC caused by stratiform clouds. Approximately 60% RC of seven cases is associated with cloud-to-ground lightning flashes activities. RC appears around the highest value of CGD. The moment of maximum CGD value indicates maximum precipitation and the maturity stage of MCS in the future of 1-3 h. When CGD decrease or increase is not obvious, the rainfall intensity of RC weakens, and MCS is in the dissipation phase. Mesoscale convergence line on the dense surface wind field is prior to the MCS and RC, and the local convergence caused by mesoscale convergence line can be used as starting mechanism of MCS development.
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图 6 个例2中2011年7月18日06:00—13:00逐时地闪密度 (填色) 和1 h降水量
(等值线,单位:mm,最小值为10 mm, 间隔为10 mm)(虚线矩形为所研究正、负地闪区域)
Fig. 6 CG lightning density (the shaded) and 1 h precipitation (the contour, unit:mm, the minimun is 10 mm, interval is 10 mm) from 0600 BT to 1300 BT on 18 Jul 2011 of Case 2 (the dotted rectangle represents the target region of positive and negative CG lighting)
图 7 个例5中2012年7月20日14:00—23:00逐时地闪密度 (阴影) 和1 h降水量
(等值线,单位:mm,最小值为10 mm, 间隔为10 mm)(虚线矩形为所研究正、负地闪区域)
Fig. 7 CG lightning density (the shaded) and 1 h precipitation (the contour unit:mm, the minimum is 10 mm, interval is 10 mm) from 1400 BT to 2300 BT on 20 Jul 2012 of Case 5 (the dotted rectangle represents the target region of positive and negative CG lighting)
图 9 个例5中2012年7月20日14:00—21日08:00自动气象站风场 (风羽)、辐合线 (双实线)、逐时TBB (填色) 和1 h降水量 (等值线,单位:mm,最小值为10 mm, 间隔为10 mm)
Fig. 9 Wind field of automatic weather stations (the barb), convergence line (double solid lines), TBB (the shaded) and 1 h precipitation (the contour, unit:mm, the minimum is 10 mm, interval is 10 mm) from 1400 BT 20 Jul to 0800 BT 21 Jul in 2012 of Case 5
表 1 暴雨个例影响时间、范围和强度概况以及雨团特征
Table 1 Influence time, occurring area, intensity and rain cluster characteristics of torrential rain cases
个例编号 时间 持续日数/d 影响地区 暴雨站次 原地生消雨团过程 移动雨团过程 个例1 2009-08-16—20 4 5 9 3 0 个例2 2011-07-15—21 6 3 6 2 1 个例3 2011-07-23—27 4 4 10 4 1 个例4 2012-06-24—29 5 3 4 2 2 个例5 2012-07-19—22 3 8 27 0 3 个例6 2012-07-24—31 7 9 18 2 2 个例7 2013-07-14—16 3 7 19 1 2 -
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