Heavy rainfall is one kind of extreme weather which is harmful to human beings. Since the formation mechanism of heavy rainfall is very complicated, it brings great challenge to weather forecasting and warning. An unusual double-belt heavy rainfall with high precipitation intensity and long-duration precipitation happened on July 1st 2013 around Beijing-Tianjin-Hebei area, under the synoptic background of northwards stretching subtropical high, southwards strengthening low-level jets, and eastwards moving upper trough. The formation mechanism and mesoscale characteristics of this case is analyzedbased on conventional observation, NCEP (National Centers for Environmental Prediction) reanalysis data, multi-type of intensive observation, and the variational radar data assimilation. The result shows that thosetworainfall belt promote mutually, although their formation mechanism and mesoscale evolution differ obviously. The south branch heavy rainfall belt occurred under the strengthened southwest warm and moist environment, with high convective instability and deep moist layers. The heavy rainfall is triggered, organized by the warm mesoscale convergence line and developed by MCC(Mesoscale Convective Complex). The radar echoes of the rainfall is characteristic of "train-effect" and backpropagation. It is a deeper warm-zone wet convection rainstorm with extremely high rainfall intensity, large amount of accumulated rainfall, and obvious mesoscale features. The location of rainfall belt and the extremely intensive precipitation core is dominated by the position of the surface convergence line and the mesoscale eddies. Propagating direction of the intense radar reflectivity is indicated by the cold pool outflow generated by heavy rainfall together with the maximum temperature gradient formed by the southerly warm and wet airflow. The north branch heavy rainfall belt is brought about by multi-cell echoes belt formed by shearline cloud system, under the influence of cold shear line and low-level low vortex. It sinstability energy is lower than that in the south branch heavy rainfall belt, but the upward motion is stronger thanks to the coupling action of the upper and lower synoptic systems. Intrusion of dry and cold air in middle layer forms an obvious θse frontal zone. It is a frontal convective system. Meanwhile, the terrain helps to enhance precipitation markedly. Various factors jointly make the case be characteristic of relative weak rainfall intensity, long-lasting precipitation and large area with heavy rain. The moving path of the low-level low vortex is well consistent with the location of the rainfall belt and heavy rainfall region. The easterly wind induced by warm-zone precipitation within the south branch heavy rainfall belt not only brings water vapor to the north branch rainfall belt but also the orographic lifting made by the Taihang mountain benefits the occurrence and development of those severe convection cells, which furtherly enhance the rainfall intensity of the north branch rainfall belt. On the other hand, the cold pool formed by severe convective rainfall accelerates the formation of surface mesoscale eddies, which cause intense convective radar echoesmergence and strengthen the rainfall again at the later stage of the south branch rainfall belt.
[1]Davis R S, 2001. Flash flood forecast and detection methods:Severe convective storms[J]. American Meteorological Society, 28(50):481-525.
[2]Doswell C A Ⅲ, Brooks H E, Maddox R A, 1996. Flash flood forecasting:An ingredients-based methodology[J]. Weather and Forecasting, 11(4):560-581.
[3]Sun J Z, Crook N A, 1997. Dynamical and microphysical retrieval from Doppler radar observations using a cloud model and its adjointI:Model development and simulated data experiments[J]. Journal of the Atmospheric Sciences, 54(12):1642-1661.
[4]Sun J Z, Crook N A, 1998. Dynamical and microphysical retrieval from Doppler radar observations using a cloud model and its adjoint Ⅱ:Retrieval experiments of an observed Florida convective storm[J]. Journal of the Atmospheric Sciences, 55 (5):835-852.
[5]Sun J Z, Crook N A, 2001. Real-time low-level wind and temperature analysis using single WSR-88D data[J]. Weather and Forecasting, 16(1):117-132.
[6]Sun J Z, Zhang Y, 2008. Analysis and prediction of a squall line observed during IHOP using multiple WSR-88D observations[J]. Monthly Weather Review, 136(7):2364-2388.
[7]陈明轩, 王迎春, 高峰, 等, 2011.基于雷达资料4DVar的低层热动力反演系统及其在北京奥运期间的初步应用分析[J].气象学报, 69(1):64-78.
[8]丁治英, 常越, 朱莉, 等, 2008.1958-2000年6月连续性暴雨的特征分析[J].热带气象学报, 24(2):117-126.
[9]丁治英, 朱莉, 常越, 等, 2009.一次连续性暴雨中双雨带的成因分析[J].热带气象学报, 25(6):697-705. DOI:10.3969/j.issn.1004-4965.2009.06.008.
[10]孔凡超, 赵庆海, 李江波, 2016.2013年7月冀中特大暴雨的中尺度系统特征和环境条件分析[J].气象, 42(5):578-588. DOI:10.7519/j.issn.1000-0526.2016.05.007.
[11]廖晓农, 倪允琪, 何娜, 等, 2013.导致"7·21"特大暴雨过程中水汽异常充沛的天气尺度动力过程分析研究[J].气象学报, 71(6):997-1011. DOI:10.11676/qxxb2013.081.
[12]吕晓娜, 2017.河南一次强对流天气潜势、触发与演变分析[J].高原气象, 36(1):195-206. DOI:10.7522/j.issn.1000-0534.2016.00023.
[13]苗爱梅, 郝振荣, 贾利冬, 等, 2014. "0702"山西大暴雨过程的多尺度特征[J].高原气象, 33(3):786-800. DOI:10.7522/j.issn.1000-0534.2013.00014.
[14]孙建华, 赵思雄, 傅慎明, 等, 2013.2012年7月21日北京特大暴雨的多尺度特征[J].大气科学, 37(3):705-718. DOI:10.3878/j.issn.1006-9895.2013.12202.
[15]孙继松, 何娜, 王国荣, 等, 2012. "7·21"北京大暴雨系统的结构演变特征及成因初探[J].暴雨灾害, 31(3):218-225.
[16]孙靖, 程光光, 2017.北京城区热动力条件对雷暴下山后强度的影响[J].高原气象, 36(1):207-218. DOI:10.7522/j.issn.1000-0534.2016.00007.
[17]孙明生, 李国旺, 尹青, 等, 2013. "7·21"北京特大暴雨成因分析(Ⅰ):天气特征、层结与水汽条件[J].暴雨灾害, 32(3):210-217. DOI:10.3969/j.issn.1004-9045.2013.03.003.
[18]孙明生, 杨力强, 尹青, 等, 2013. "7·21"北京特大暴雨成因分析(Ⅱ):垂直运动、风垂直切变与地形影响[J].暴雨灾害, 32(3):218-223. DOI:10.3969/j.issn.1004-9045.2013.03.004.
[19]孙永刚, 孟雪峰, 仲夏, 等, 2014.河套气旋发展东移对一次北京特大暴雨的触发作用[J].高原气象, 33(6):1665-1673. DOI:10.7522/j.issn.1000-0534.2014.00029.
[20]谭冠日, 严济远, 朱瑞兆, 1985.应用气候[M].上海:上海科学技术出版社, 229.
[21]汤鹏宇, 何宏让, 阳向荣, 等, 2015.北京"7·21"特大暴雨中的干侵入分析研究[J].高原气象, 34(1):210-219. DOI:10.7522/j.issn.1000-0534.2013.00128.
[22]王婧羽, 崔春光, 王晓芳, 等, 2014.2012年7月21日北京特大暴雨过程的水汽输送特征[J].气象, 40(2):133-145. DOI:10.7519/j.issn.1000-0526.2014.02.001.
[23]吴正华, 1992.华北暴雨[M].北京:气象出版社, 9-12.
[24]杨青, 阎琦, 陈力强, 等, 2015.辽宁一次典型双雨带暴雨过程分析[J].气象与环境学报, 31(6):34-42. DOI:10.3969/j.issn.1673-503X. 2015.06.005.
[25]俞小鼎, 2012.2012年7月21日北京特大暴雨成因分析[J].气象, 38(11):1313-1329.
[26]俞小鼎, 2013.短时强降水临近预报的思路与方法[J].暴雨灾害, 32(3):202-209. DOI:10.3969/j.issn.1004-9045.2013.03.002.
[27]章国材, 2011.强对流天气分析与预报[M].北京:气象出版社, 98-100.
[28]张迎新, 李宗涛, 姚学祥, 2015.京津冀"7·21"暴雨过程的中尺度分析[J].高原气象, 34(1):202-209. DOI:10.7522/j.issn.1000-0534.2013.00096.
[29]赵桂香, 薄燕青, 邱贵强, 等, 2017.黄河中游一次大暴雨的观测分析与数值模拟[J].高原气象, 36(2):436-454. DOI:10.7522/j.issn.1000-0534.2016.00093.
[30]赵庆云, 傅朝, 刘新伟, 等, 2017.西北东部暖区大暴雨中尺度系统演变特征[J].高原气象, 36(3):697-704. DOI:10.7522/j.issn.1000-0534.2016.00140.
[31]赵玉春, 李泽椿, 肖子牛, 2008.华南锋面与暖区暴雨个例对比分析[J].气象科技, 36(1):47-54.
[32]郑维忠, 余志豪, 黄菲, 1999.梅雨锋暴雨个例的中尺度数值模拟研究(Ι)-中<i>α</i>尺度双雨带[J].南京大学学报(自然科学), 35(3):346-354.
