一次冷性停滞型西南低涡结构的演变特征
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摘要
利用常规气象观测资料、NCEP(National Centers for Environmental Prediction,美国国家环境预报中心)再分析资料、雷达资料、卫星以及区域站资料等对2015年8月16日08:00(北京时,下同)至18日20:00四川盆地持续性大暴雨过程作了系统分析。结果表明:在西太平洋副热带高压(下称西太副高)阻塞形势下,高原涡东侧和西太副高西北侧的正涡度平流共同为西南低涡提供动力条件,前侧温度槽叠加在中低层暖性浅薄天气系统上加强了对流不稳定,冷空气缓慢侵入造成冷性停滞型西南低涡持续发展;西南低涡中的降水通过凝结潜热释放作用与西南低涡相伴增强;西南低涡成熟阶段,高低层正涡度柱几乎垂直耦合,水平流场形态上表现为近圆形,700 hPa温度、水汽及能量场均表现为"S"形非对称形态,有利于中低层维持向东北部的暖湿输送机制,这是纬向降水强于经向的重要因素;盆地地形条件下,纬向降水主要是中心中尺度对流系统MCSs(Mesoscale Convective Systems)两次稳定发展的结果,降水集中在西南低涡暖切变线南侧,地面静止锋附近,而经向降水主要是两次冷锋MCSs降水,位于西南低涡低槽前部;西南低涡中MCSs活动分为八个阶段,在动力机制维持情况下,西南低涡南侧MCSs通过影响水汽输送对中心MCSs发展形成制约机制,西南低涡东北部和东南部降水呈现此消彼长的"跷跷板"发展特征。
By using data from conventional soundings and surface observation,NCEP reanalysis,radar,satellite and regional automatic stations,an incessant heavy rainstorm from 16 to 18 August 2015 in Sichuan Basin was systematically analyzed. The results showed that being blocked by the West Pacific Subtropical High (WPSH),the positive vorticity advection to the eastern side of the plateau vortex and the northwestern side of the WPSH provide the dynamic conditions for the Southwest Vortex (SV),the front temperature trough superimposed on the middle and lowwarm shallowsynoptic systems strengthens the convective instability,the cold air invading slow-ly results in the stationery cold SV sustainable development. The precipitation in SV is enhanced by condensation latent heat release. In the maturation stage of SV,the vertical positive vorticity column at all levels is almost vertically coupled. The horizontal flowpattern approximately forms as a circle,while the temperature,moisture and energy fields at 700 hPa asymmetrically shape as "S". It is beneficial to maintain the heat and moisture transport mechanism to the northeast region of Chongqing at lower level,which is a crucial factor explaining why horizontal precipitation is stronger than that of meridian. Located in the basin area,the precipitation results from the stable development of central MCSs twice,clustering to the southern side of the warm shear of the SV,near the stationery front on the surface. In contrast,meridian precipitation is the outcome of MCSs triggered by cold front twice,located ahead of the trough of SV. The life history of MCSs could be divided into eight stages. With the maintenance of dynamic pump,the MCSs to the southern side of SV inhibits the evolution of central MCSs by influencing vapor transfer,resulting in the "see-saw"feature of the development of precipitation to the northeast and southeast of SV.
By using data from conventional soundings and surface observation,NCEP reanalysis,radar,satellite and regional automatic stations,an incessant heavy rainstorm from 16 to 18 August 2015 in Sichuan Basin was systematically analyzed. The results showed that being blocked by the West Pacific Subtropical High (WPSH),the positive vorticity advection to the eastern side of the plateau vortex and the northwestern side of the WPSH provide the dynamic conditions for the Southwest Vortex (SV),the front temperature trough superimposed on the middle and lowwarm shallowsynoptic systems strengthens the convective instability,the cold air invading slow-ly results in the stationery cold SV sustainable development. The precipitation in SV is enhanced by condensation latent heat release. In the maturation stage of SV,the vertical positive vorticity column at all levels is almost vertically coupled. The horizontal flowpattern approximately forms as a circle,while the temperature,moisture and energy fields at 700 hPa asymmetrically shape as "S". It is beneficial to maintain the heat and moisture transport mechanism to the northeast region of Chongqing at lower level,which is a crucial factor explaining why horizontal precipitation is stronger than that of meridian. Located in the basin area,the precipitation results from the stable development of central MCSs twice,clustering to the southern side of the warm shear of the SV,near the stationery front on the surface. In contrast,meridian precipitation is the outcome of MCSs triggered by cold front twice,located ahead of the trough of SV. The life history of MCSs could be divided into eight stages. With the maintenance of dynamic pump,the MCSs to the southern side of SV inhibits the evolution of central MCSs by influencing vapor transfer,resulting in the "see-saw"feature of the development of precipitation to the northeast and southeast of SV.
引文
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Kuo Y H,Cheng L S,Anthes R A,1986.M esoscale analyses of the Sichuan flood catastrophe,11-15 July 1981[J].M on Wea Rev,114(11):1984-2003.
Kuo Y H,Cheng L S,Bao J W,1988.Numerical simulation of the1981 Sichuan flood.Part I:Evolution of a mesoscale southw est vortex[J].M on Wea Rev,116(12):2481-2504.
Wang W,Kuo Y H,Thomas T W,1993.A diabatically driven mesoscale vortex in the lee of the Tibetan Plateau[J].M on Wea Rev,121(9):2542-2561.
陈贵川,谌芸,张勇,等,2013.“12·7·21”西南涡极端强降雨的成因分析[J].气象,39(12):1529-1541.Chen G C,Chen Y,Zhang Y,et al,2013.Causes analysis of the southw est vortex extremely heavy rainfall on 21 july 2012[J].M eteor M on,39(12):1529-1541.
陈永仁,李跃清,2013.“12·7·22”四川暴雨的MCS特征及对短时强降雨的影响[J].气象,39(7):848-860.Chen Y R,Li YQ,2013.Characteristics of mesoscale convective system and its effects on short-time severe rainfall in sichuan basin during 21-22july 2012[J].M eteor M on,39(7):848-860.
陈忠明,1989.环境场作用与西南低涡移动的初步分析[J].高原气象,8(4):301-312.Chen Z M,1989.The preliminary study of effect of environment flow fields on movement of southw est vortex[J].Plateau Meteor,8(4):301-312.
陈忠明,廖强,闵文彬,1998.一次强烈发展西南低涡的中尺度结构分析[J].应用气象学报,9(3):273-282.Chen Z M,Miao Q,M in W B,1998.A case analysis on mesoscale structure of severe southw est vortex[J].Quart J Appl M eteor,9(3):273-282.
陈忠明,闵文彬,缪强,等,2004.高原涡与西南低涡相互耦合作用的个例诊断[J].高原气象,23(1):75-80.Chen Z M,Min WB,M iao Q,et al,2004.A case study on coupling interaction betw een plateau and southw est vortexes[J].Plateau M eteor,23(1):75-80.
段海霞,陆维松,毕宝贵,2008.凝结潜热与地表热通量对一次西南低涡暴雨影响分析[J].高原气象,27(6):1315-1321.Duan HX,Lu W S,Bi B G,2008.Impact of the condensation heating and surface heat flux on a rainstorm event of southw est vortex[J].Plateau M eteor,27(6):1315-1321.
顾清源,周春花,青泉,等,2008.一次西南低涡特大暴雨过程的中尺度特征分析[J].气象,34(4):39-47.Gu Q Y,Zhou C H,Qing Q,et al,2008.M esoscale characteristics analysis of severe torrential rain caused by a southw estern low vortex process[J].M eteor M on,34(4):39-47.
郝丽萍,周瑾,康岚,2016.西南涡暴雨天气过程分析和数值模拟试验[J].高原气象,35(5):1182-1190.Hao L P,Zhou J,Kang Lan,2016.Weather analyses and numerical study of Southw est China vortex and its induced heavy rainfall[J].Plateau M eteor,35(5):1182-1190.DOI:10.7522/j.issn.1000-0534.2015.00046.
何光碧,2012.西南低涡研究综述[J].气象,38(2):155-163.He GB,2012.Review of the southw est vortex research[J].M eteor M on,38(2):155-163.
黄福均,1986.西南低涡的合成分析[J].大气科学,10(4):402-408.Huang F J,1986.A composite analysis of the southw est vortex[J].Scientia Atmospherica Sinica,10(4):402-408.
李超,李跃清,蒋兴文,2017.夏季长生命史盆地涡活动对川渝季节降水的影响[J].高原气象,36(3):685-696.Li C,Li Y Q,Jiang X W,2017.M echanism of long lifespan Sichuan Basin vortex's activity influence the precipitation in Sichuan-Chongqing region on summer[J].Plateau M eteor,36(3):685-696.DOI:10.7522/j.issn.1000-0534.2016.00064.
李国平,万军,卢敬华,1991.暖性西南低涡形成的一种可能机制[J].应用气象学报,2(1):91-99.Li G P,Wan J,Lu J H,1991.A potential mechanism of the w arm vortex genesis in southw est china[J].Quart J Appl M eteor,2(1):91-99.
李国庆,陈瑞荣,杨广基,等,1976.青藏高原东南部低涡的初步模拟试验[J].中国科学(3):286-294.Li G Q,Chen R R,Yang G J,et al,1976.A preliminary simulative experiment of the vortex to the southeast of Tibetan Plateau[J].China Science(3):286-294.
李黎,刘海文,吕世华,2017.春季西南低涡年际和年代际变化特征分析[J].高原气象,36(6):1512-1520.Li L,Liu H W,Lu SH,2017.Interannual and interdecadal variations analysis of the spring Southw est Vortex[J].Plateau M eteor,36(6):1512-1520.DOI:10.7522/j.issn.1000-0534.2017.00016.
罗四维,1977.青藏高原东侧动力性低涡形成机理的分析[J].气象科技(增刊):54-65.Luo S W,1977.An analysis of formation of the dynamic vortex to the east side of Tibetan Plateau[J].M eteor Sci Technol(suppl):54-65.
罗四维,1992.青藏高原及其邻近地区几类天气系统的研究[M].北京:气象出版社,56-96.Luo S W,1992.A study of several synoptic systems on Tibetan Plateau and adjacent areas[M].Beijing:China M eteorological Press,56-96.
卢敬华,1986.西南低涡概论[M].北京:气象出版社,58,129-146.Lu J H,1988.Introduction to the southw est vortex[M].BeiJing:China M eteotological Press,58,129-146.
卢萍,李跃清,郑伟鹏,等,2014.影响华南持续性强降水的西南涡分析和数值模拟[J].高原气象,33(6):1457-1467.Lu P,Li Y Q,Zheng W P,et al,2014.Analysis and numerical simulation of southw est vortex on continuous heavy rain processes in south china[J].Plateau M eteor,33(6):1457-1467.DOI:10.7522/j.issn.1000-0534.2013.00137.
彭新东,程麟生,1994.高原东侧低涡切变线发展的个例数值研究:Ⅱ中尺度数值模拟[J].兰州大学学报(自然科学),30(1):124-131.Peng X D,Cheng L S,1994.A case numerical study on the evolution of the low vortex and shear-1ine on the east side of the plateau:Ⅱmesoscale numerical simulation[J].Journal of Lanzhou University(Natural Sciences),30(1):124-131.
陶诗言,1980.中国之暴雨[M].北京:科学出版社,1-7.Tao S Y,1980.China Storms[M].BeiJing:China Science Press,1-7.
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