利用常规观测资料、NCEP/NCAR的1°×1°再分析资料和WRF3.2模式的模拟结果分析了一次由台风"海鸥"与西风槽远距离相互作用产生的山东暴雨过程的水汽和干冷空气活动。结果表明:水汽辐合主要来自南边界的水汽流入,南边界水汽输入的增强主要是台风向北的水汽输送造成的,对流层低层的低涡使水汽在山东中西部地区集中。南北方向水汽辐合的大小与降水量有较好的对应关系。暴雨过程中有明显干冷空气活动,暴雨初期,对流层顶的干冷空气先行侵入降水区,引起高层西风加速和辐散加强,进而导致上升运动发展。暴雨发展期,对流层中层(500 hPa或600 hPa)干冷空气由西北向东南以偏西气流的方式侵入降水区,与暖湿空气以东西风的形式辐合上升。暴雨强盛期,对流层中层不仅有来自中纬度西北方向的干冷空气侵入,而且还有来自高纬的干冷空气侵入。干侵入始终具有高层超前于低层的特点,有利于位势不稳定的发展。干冷空气与暖湿空气活动的加强使山东地区中低层锋生加强,激发非地转垂直上升运动,是上升运动加强的机制之一。暴雨过程中对流性不稳定和条件性不稳定共存,干冷空气侵入使等相当位温面倾斜及强迫暖湿气流沿锋面倾斜上升,有利于条件性对称不稳定的发展。
A heavy rainfall event that occurred in Shandong Province on 17-19 July 2008 was caused by the interaction between typhoon Haiou and westerly trough. The water vapor and the activities of dry and cold air of this heavy rainfall event were studied by using routine observation, NCEP/NCAR 1°×1° reanalysis and simulated data from the WRF3.2 model. The results show that the water vapor convergence was mainly from the inflow of the southern boundary. The intensification of the inflow of the water vapor from southern boundary primarily contributed to the northward transportation of water vapor from the typhoon. The convergence of water vapor in the west and middle parts of Shandong Province resulted from the vortex in the lower troposphere. The convergence of water vapor in the south-north direction corresponded well with rainfall. Dry and cold air apparently intruded into rainfall area in the process of the rainfall. In the initial phase of the heavy rainfall, dry and cold air in the tropopause first intruded into the rainfall area and induced the acceleration of west wind in the high levels and the enhancement of divergence, which led to the development of upward motion. In the development phase of the heavy rainfall, dry and cold air in the middle troposphere (500 hPa or 600 hPa) intruded into rainfall area with westerly wind from northwest to southeast and met with warm and moist air, resulted in upward motion. In the heavy rainfall period, dry and cold air came not only from northwest in the mid-latitude but also from the high latitudes. Dry intrusion in the higher levels was always ahead of that in the lower levels, which is favorable to the development of potential instability. The activities of dry and cold air as well as warm and moist air intensified frontogenesis in the lower and middle levels in Shandong Province and ageostrophic ascending motion was triggered, which is one of the mechanisms of the intensification of the ascending motion. Convective instability and conditional symmetric instability existed in the heavy rainfall event. Dry intrusion can slant the equivalent potential temperature surface and force warm and moist air to move upward slantwise along front, which is beneficial to the development of conditional symmetric instability.
[1]Bennetts D A,Hoskins B J. 1979. Conditional symmetrical instability-possible explanation for front rainbands[J]. Quart J Roy Meteor Soc,105:945-962.
[2]Bosart L F,Carr F H. 1978. A case study of excessive rainfall centered around Wellsville,New York,20-21 June 1972[J]. Mon Wea Rev,106:348-362.
[3]Browing K A,Golding B W. 1995. Mesoscale aspects of a dry intrusion within a vigorous cyclone[J]. Quart J Roy Meteor Soc,121:463-493.
[4]Browning K A,Roberts N M. 1994. Structure of a frontal cyclone[J]. Quart J Roy Meteor Soc,120:1535-1557.
[5]Browning K A,Roberts N M. 1996. Variation of frontal and precipitation structure along a cold front[J]. Quart J Roy Meteor Soc,122:1845-1872.
[6]Browning K A. 1997. The dry intrusion perspective of extra-tropical cyclone development[J]. Meteor Appl,4(4):317-324.
[7]Cote M R. 2007. Predecessor rain events in advance of tropical cyclones[D]. New Yrak:Department of Atmospheric and Environmental Sciences,University at Albany,State University of New York,1-200. http://cstar.cestm.albany.edu/CAP_Projects/Project10/index.htm.
[8]Danielsen E F. 1964. Project Springfield Report[R]. Washington D C:Defense Atomic Support Agency,99.
[9]DiMego G J,Bosart L F. 1982a. The transformation of tropical storm Agnes into an extratropical cyclone. Part I:The observed fields and vertical motion computations[J]. Mon Wea Rev,110:385-411.
[10]DiMego G J,Bosart L F. 1982b. The transformation of tropical storm Agnes into an extratropical cyclone. Part II:Moisture,vorticity and kinetic energy budgets[J]. Mon Wea Rev,110:412-433.
[11]Elsberry R L. 2002. Predicting hurricane landfall precipitation:optimistic and pessimistic views from the symposium on precipitation extremes[J]. Bull Amer Meteor Soc,83:1333-1339.
[12]Emanual K A. 1983. On assessing local conditional symmetric instability from atmospheric sounding[J]. Mon Wea Rev,111:2016-2033.
[13]Galarneau T J,Bosart L F,Schumacher R S. 2010. Predecessor rain events ahead of tropical cyclones[J]. Mon Wea Rev,138:3272-3297.
[14]Gao S,Meng Z,Zhang F,et al. 2009. Observational analysis of heavy rainfall mechanisms associated with severe tropical storm Bilis (2006) after its landfall[J]. Mon Wea Rev,137:1881-1897.
[15]Huang H L,Yang M J,Sui C H. 2014. Water budget and precipitation efficiency of typhoon Morakot (2009)[J]. J Atmos Sci,71:112-129.
[16]Lemon L R. 1998. On the mesocyclone ‘dry intrusion’ and tornadogesis[C]//Preprints,19<sup>th</sup> Conference on Severe Local Storms. Minneapolis:Amer Meteor Soc,752-755.
[17]Schumacher R S,Galarneau T J,Bosart L F. 2010. Distant effects of a recurving tropical cyclone on rainfall in a midlatitude convective system:a high-impact predecessor rain event[J]. Mon Wea Rev,139:650-667.
[18]Wang Y,Wang Y,Fudeyasu H. 2009. The role of typhoon Songda (2004) in producing distantly located heavy rainfall in Japan[J]. Mon Wea Rev,137:3699-3716.
[19]Yang M J,Ching L. 2005. A modeling study of typhoon toraji (2001):Physical parameterization sensitivity and topographic effect[J]. Terr Atmos Ocean Sci,16(1):177-213.
[20]白涛,李崇银,王铁,等. 2013. 干侵入对陕西"2008.07.21"暴雨过程的影响分析[J]. 高原气象,32(2):345-356. Bai Tao,Li Chongyin,Wang Tie,et al. 2013. Analysis of influence of dry intrusion on rainstorm on 21 July 2008 in Shaanxi Province[J]. Plateau Meteor,32(2):345-356. DOI:10.7522/j.issn. 1000-0534.2012.00034.
[21]陈联寿,丁一汇. 1979. 西太平洋台风概论[M]. 北京:科学出版社,8-9. Chen Lianshou,Ding Yihui. 1979. Introduction to the Western Pacific Typhoon[M]. Beijing:Science Press,8-9.
[22]丛春华,陈联寿,雷小途,等. 2012. 热带气旋远距离暴雨的研究[J]. 气象学报,70(4):717-727. Cong Chunhua,Chen Lianshou,Lei Xiaotu,et al. 2012. A study on the mechanism of the tropical cyclone remote precipitation[J]. Acta Meteor Sinica,70 (4):717-727.
[23]龚佃利,王庆,刘诗军. 2006. 山东一次春季暴雨过程的水汽收支和降水转化数值分析[J]. 气候与环境研究,11(1):109-118. Gong DianLi,Wang Qing,Liu Shijun. 2006. The numerical analysis about water vapor budget and transform during a spring heavy rain process in Shandong region[J]. Climatic Environ Res,11(1):109-118.
[24]杨仁勇,闵锦忠,郑艳. 2014. 强台风"纳沙"引发的特大暴雨过程数值试验[J]. 高原气象,33(3):753-761. Yang Renyong,Min Jinzhong,Zheng Yan. 2014. Numerical simulations of the extraordinary rainstorm by typhoon Nesat[J]. Plateau Meteor,33(3):753-761. DOI:10.7522/j.issn. 1000-0534.2013.00047.
[25]刘会荣,李崇银. 2010. 干侵入对济南"7.18"大暴雨的作用[J]. 大气科学,34(2):374-386. Liu Huirong,Li Chongyin. 2010. Impacts of the dry intrusion on Ji'nan torrential rain occurring on 18 July 2007[J]. Chinese J Atmos Sci,34(2):374-386.
[26]孙建华,赵思雄. 2000. 登陆台风引发的暴雨过程之诊断研究[J]. 大气科学,24(2):223-237. Sun Jianhua,Zhao Sixiong. 2000. Diagnoses and simulations of typhoon (Tim) landing and producing heavy rainfall in China[J]. Chinese J Atmos Sci,24(2):223-237.
[27]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. Tang Pengyu,He Hongrang,Yang Xiangrong,et al. 2015. Research and analysis of dry intrusion during Beijing ‘7.21’ extreme torrential rain[J]. Plateau Meteor,34(1):210-219. DOI:10.7522/j.issn. 1000-0534.2013.00128.
[28]陶诗言. 1980. 中国之暴雨[M]. 北京:科学出版社,1-225. Tao Shiyan. 1980. Heavy rainfalls in China[M]. Beijing:Science Press,1-225.
[29]王培,沈新勇,高守亭. 2012. 一次东北冷涡过程的数值模拟与降水分析[J]. 大气科学,36(1):130-144. Wang Pei,Shen Xinyong,Gao Shouting. 2012. A numerical study and rainfall analysis of a cold vortex process over Northeast China[J]. Chinese J Atmos Sci,36(1):130-144.
[30]吴国雄,蔡雅萍,唐晓菁. 1995. 湿位涡和倾斜涡度发展[J]. 气象学报,53(4):387-404. Wu Guoxiong,Cai Yaping,Tang Xiaojing. 1995. Moist potential vorticity and slantwise vorticity development[J]. Acta Meteor Sinica,53(4):387-404.
[31]武麦凤,王桂梅,曹玲玲,等. 2014. 台风"洛克"远距离引发陕西暴雨过程的成因分析[J]. 高原气象,33(5):1297-1304. Wu Maifeng,Wang Guimei,Cao Lingling,et al. 2014. Analysis on rainstorm in Shaanxi distance caused by typhoon ‘Roke’[J]. Plateau Meteor,33(5):1297-1304. DOI:10.7522/j.issn. 1000-0534.2013.00072.
[32]姚秀萍,于玉斌. 2005.2003年梅雨期干冷空气的活动及其对梅雨降水的作用[J]. 大气科学,29(6):973-985. Yao Xiuping,Yu Yubin. 2005. Activity of dry cold air and its impacts on Meiyu rain during 2003 Meiyu period[J]. Chinese J Atmos Sci,29(6):973-985.
[33]赵宇,崔晓鹏,高守亭. 2011. 引发华北特大暴雨过程的中尺度对流系统结构特征研究[J]. 大气科学,35(5):945-962. Zhao Yu,Cui Xiaopeng,Gao Shouting. 2011. A study of structure of mesoscale systems producing a heavy rainfall event in North China[J]. Chinese J Atmos Sci,35(5):945-962.
[34]赵宇,李媛,赵光平. 2013. 引发暴雨天气的中尺度低涡的数值研究[J]. 大气科学学报,36(6):751-763. Zhao Yu,Li Yuan,Zhao Guangping. 2013. A numerical study on a mesoscale vortex producing a heavy rainfall event[J]. Transactions Atmos Sci,36(6):751-763. DOI:10.3969/j.issn. 1674-7097.2013.06.012.
[35]朱洪岩,陈联寿,徐祥德. 2000. 中低纬度环流系统的相互作用及其暴雨特征的模拟研究[J]. 大气科学,24(5):669-675. Zhu Hongyan,Chen Lianshou,Xu Xiangde. 2000. A numerical study of the interactions between typhoon and mid-latitude circulation and its rainfall characteristics[J]. Chinese J Atmos Sci,24(5):669-675.