华北一次强对流天气的诊断分析和数值模拟研究
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摘要
强对流天气是华北夏季的主要灾害之一,常常引发雷暴、大风、冰雹和暴雨等灾害性天气,危害极大。对该类系统的监测、预报和研究一直是许多气象业务和科研人员关注的热点。本文运用常规的地面观测资料、NCEP再分析资料,对2009年6月8日发生在华北地区的一次强对流天气过程进行了诊断分析,并用WRF模式对此次强对流天气过程进行了模拟,在模拟结果较理想的基础上,探讨了此次暴雨发生、发展的特征和机理,得出如下结论：
(1)这次华北强对流暴雨发生在非常有利的天气形势下。蒙古低涡东移南压,伴随着高空锋区的南压,冷空气南下渗透；副热带高压北上,并产生低空急流,低空急流为强对流暴雨提供了较强的水汽输送和辐合上升运动,高空急流为这次天气提供了强的风垂直切变和高层强的正涡度平流,产生了较大的垂直上升运动。强对流暴雨就发生在低空急流的左前侧和高空急流核的左前侧。高低空急流的耦合是此次强对流天气过程形成的可能动力机制。
(2)这次强对流暴雨具备了较好的热力条件,发生在低层高湿脊内,且有较好的水汽输送,具有对流不稳定层结和对称不稳定层结,具有较强的不稳定能量。但强对流暴雨不是发生在层结最不稳定和对流不稳定能量CAPE最大的位置,而是发生在在MPV、MPV1、MPV2的零值附近的正负过渡带内,对流不稳定和斜压不稳定相结合的区域和CAPE强中心的下游。对流层高层600 hPa以上湿位涡正压项(MPV1)正的大值区与对流层低层的负值中心,正负值垂直迭加的区域有利于暴雨的发生发展。
(3)WRF模式具有很强的模拟能力,几次不同微物理过程参数化的模拟试验都能较为理想的模拟出这次过程,特别是试验(exp7),微物理过程采用新Thompson冰雹方案,对于这次华北地区的强对流暴雨过程的发生、发展,在模式结果中都有很好的描述。可以用来揭示了这次强对流暴雨的发生、发展的规律和可能机制。
(4)通过对模拟结果的分析,发现这次强对流暴雨中两段主要强对流降水发生的机制有所不同：第一时段8日6-9时,主要是副热带高压北上和低空急流的加强北上,带来了丰富的暖湿气流和低层的辐合,同时地面的东北风带来的冷空气抬上了南边的暖湿气流,触发了对流,产生强降水和大风等对流性天气；第二个时段强对流天气(14-18时),是高空西来槽东移南压和冷空气南下,华北地区锋生,加上高、低空急流的动力作用产生的。
The heavy convective storm is one of the primary disastrous weather in summer in North China, such as thunder, windstorm, hail and heavy rain etc, which often cause great hazards. It has been the hotspot for the meteorologists all the time to monitor, forecast and study this system. Based on observed data and NCEP reanalyzed data, a case of strong convective storm occurring in North China on June 8,2009 was analyzed, furthermore, the process of the storm was simulated using WRF model, discussing the feature and mechanism of the system and getting the following conclusions:
(1) Under the favourable weather situation, Mongolian vortex moved towards east and spreaded to south, cold air moved towards south with the moving of high frontal zone. Accompanied by the spreading towards north of West Pacific Subtropical high, the low-level jet came into being, which provided the delivery of strong vapour and strong convergence climbing movement for heavy convective rainstorm.upper-level jet provided strong vertical wind shear and positive vorticity advection for the rainstorm, this resulted in powerful ascending motion.Rainstrom occurred in the left side of low-level and upper-level jet, and the coupling of them may be the dynamics mechanism of this process.
(2) Better thermal condition,high temperature and humidity ridge of low-level, better vapour transmission, convective unstable stratification and symmetrical unstable stratification,led to strong unstable energy. This convective storm took place nearby the zero line of MPV, MPV1 and MPV2, the combination region of convective instability and barocline instability and downstream of the middle of CAPE. It is advantage to the development of the strong convective rainstorm that plus MPV1 zone above 600 hPa just over minus one at lower levels.
(3) For WRF model has a great simulation capability, this process has been successfully simulated by using WRF model through simulated tests of several different microphysical process parameterization, new Thompson hail scheme was adopted in exp7. Model results showed very well all the occurrence and development of this convective rainstorm of North China, it also can be used to reveal the rules and mechanisms of development of the strong convection.
(4) Two main precipitation period has different occurrence mechanisms, which was confirmed by analysing model results. In the first session, at 6-9 am,in June 8,2009, with West Pacific Subtropical high and low-level jet moving towards north, plentiful vapour delivered northword and convergence at lower level strengthened, at the same time, the low-level west-south warm and moist flow was lifted by cold air accompanied by suface northeasterly winds, thus a convective storm was triggered, following with strong rainfall and gale wind. In the second period, at 14-18pm,the main reason of the occurrence of this process was upper-air trough moving towards south and cold air spreading southward,which led to frontogenesis in North China, dynamic action of jet at low-level or upper-level was also an incentive.
(1)这次华北强对流暴雨发生在非常有利的天气形势下。蒙古低涡东移南压,伴随着高空锋区的南压,冷空气南下渗透；副热带高压北上,并产生低空急流,低空急流为强对流暴雨提供了较强的水汽输送和辐合上升运动,高空急流为这次天气提供了强的风垂直切变和高层强的正涡度平流,产生了较大的垂直上升运动。强对流暴雨就发生在低空急流的左前侧和高空急流核的左前侧。高低空急流的耦合是此次强对流天气过程形成的可能动力机制。
(2)这次强对流暴雨具备了较好的热力条件,发生在低层高湿脊内,且有较好的水汽输送,具有对流不稳定层结和对称不稳定层结,具有较强的不稳定能量。但强对流暴雨不是发生在层结最不稳定和对流不稳定能量CAPE最大的位置,而是发生在在MPV、MPV1、MPV2的零值附近的正负过渡带内,对流不稳定和斜压不稳定相结合的区域和CAPE强中心的下游。对流层高层600 hPa以上湿位涡正压项(MPV1)正的大值区与对流层低层的负值中心,正负值垂直迭加的区域有利于暴雨的发生发展。
(3)WRF模式具有很强的模拟能力,几次不同微物理过程参数化的模拟试验都能较为理想的模拟出这次过程,特别是试验(exp7),微物理过程采用新Thompson冰雹方案,对于这次华北地区的强对流暴雨过程的发生、发展,在模式结果中都有很好的描述。可以用来揭示了这次强对流暴雨的发生、发展的规律和可能机制。
(4)通过对模拟结果的分析,发现这次强对流暴雨中两段主要强对流降水发生的机制有所不同：第一时段8日6-9时,主要是副热带高压北上和低空急流的加强北上,带来了丰富的暖湿气流和低层的辐合,同时地面的东北风带来的冷空气抬上了南边的暖湿气流,触发了对流,产生强降水和大风等对流性天气；第二个时段强对流天气(14-18时),是高空西来槽东移南压和冷空气南下,华北地区锋生,加上高、低空急流的动力作用产生的。
The heavy convective storm is one of the primary disastrous weather in summer in North China, such as thunder, windstorm, hail and heavy rain etc, which often cause great hazards. It has been the hotspot for the meteorologists all the time to monitor, forecast and study this system. Based on observed data and NCEP reanalyzed data, a case of strong convective storm occurring in North China on June 8,2009 was analyzed, furthermore, the process of the storm was simulated using WRF model, discussing the feature and mechanism of the system and getting the following conclusions:
(1) Under the favourable weather situation, Mongolian vortex moved towards east and spreaded to south, cold air moved towards south with the moving of high frontal zone. Accompanied by the spreading towards north of West Pacific Subtropical high, the low-level jet came into being, which provided the delivery of strong vapour and strong convergence climbing movement for heavy convective rainstorm.upper-level jet provided strong vertical wind shear and positive vorticity advection for the rainstorm, this resulted in powerful ascending motion.Rainstrom occurred in the left side of low-level and upper-level jet, and the coupling of them may be the dynamics mechanism of this process.
(2) Better thermal condition,high temperature and humidity ridge of low-level, better vapour transmission, convective unstable stratification and symmetrical unstable stratification,led to strong unstable energy. This convective storm took place nearby the zero line of MPV, MPV1 and MPV2, the combination region of convective instability and barocline instability and downstream of the middle of CAPE. It is advantage to the development of the strong convective rainstorm that plus MPV1 zone above 600 hPa just over minus one at lower levels.
(3) For WRF model has a great simulation capability, this process has been successfully simulated by using WRF model through simulated tests of several different microphysical process parameterization, new Thompson hail scheme was adopted in exp7. Model results showed very well all the occurrence and development of this convective rainstorm of North China, it also can be used to reveal the rules and mechanisms of development of the strong convection.
(4) Two main precipitation period has different occurrence mechanisms, which was confirmed by analysing model results. In the first session, at 6-9 am,in June 8,2009, with West Pacific Subtropical high and low-level jet moving towards north, plentiful vapour delivered northword and convergence at lower level strengthened, at the same time, the low-level west-south warm and moist flow was lifted by cold air accompanied by suface northeasterly winds, thus a convective storm was triggered, following with strong rainfall and gale wind. In the second period, at 14-18pm,the main reason of the occurrence of this process was upper-air trough moving towards south and cold air spreading southward,which led to frontogenesis in North China, dynamic action of jet at low-level or upper-level was also an incentive.
引文
[1]Doswell.C. A. The distinction between large-scale and mesoscale contribution to severe convrction:A case study example. Wea and forecastiong.1987,3-16
[2]Brooks, H. E. Dowell C. A. The role of midtroposphric winds in the evolution and maintenance of low-level mesocyclones. Mon. Wea.. Rev.1994,122,126-136
[3]Fovell.R. G.. Numerical simulation of a midlatitude squll line in two dimention.. J. A tmas. Sci.1988,45,3846-3879
[4]Romero, R. Observations and fine grid simulations of a convective outbreak in northeastern Spain:Importance of diurnal forcing and convective cold pools. Monthly weather revies.2001,129(9),2157-2182
[5]Fiuley C. A. Numerial simulation of tornadogenesis in a high-precipitaton supercell Part Ⅰ:Storm evolution and transition into abow echo. Journal of the atmospheric sciences.2001,58(13),1597-1679
[6]Klemp J B. Dynamics of tornadic thunderstorms [J]. Ann. Rev. Fluid Mcch.,1987,19: 369-402.
[7]Rootunno R, Klemp J B, Wcsman M L. A theory for strong, long-lived squall lines [J]. J. Atmos. Sci.,1988,45:463-485.
[8]陶诗言.中国之暴雨[M].北京：气象出版社,1980：1-12.
[9]丁一汇.暴雨和中尺度气象学问题.气象学报,1994,52(3)：274-284.
[10]李耀东.动力和能量参数在强对流天气预报中的应用研究.气象学报,2004,62(4)：401-409.
[11]沈树勤.江苏冰雹强对流天气条件分析及其物理解释.气象,1994,20(9)：25-29.
[12]吴涛,黄锐,舒防国,等.”2003.6.2”十堰强对流天气雷达回波和数值模拟分析.气象科学,2005,25(6)：629-637.
[13]王欢,周军,罗树如,等,强对流活动对对流发展条件影响的数值试验.南京气象学院学报,2005,28(2)：145-152.
[14]于华英,顾松山,刘鹏,等.一次强对流过程的数值模拟.南京气象学院学报,2006,29(3)：305-313.
[15]沈树勤.沿海槽后西北气流冰雹发生条件的对比分析.气象科学,1985,5(1)：18-22.
[16]潘晓滨,陈家华.垂直风切变对风暴云影响的数值模拟.气象科学,1996,16(2)：135-143.
[17]廖玉芳,潘志祥,郭庆.基于单多普勒天气雷达产品的强对流天气预报预警方法.气象科学,2006,26(5)：564：571.
[18]杨晓霞,张爱华,贺业坤。山东省冰雹客观分县预报系统[J].气象,2002,28(10)：41-44.
[19]刘勇.急流次级环流对局地持续强风暴天气的作用[J].气象科技,2005,33(3)：214-217.
[20]寇正等.中尺度对流系统演变中的非线性对流对称不稳定.大气科学,2005,29(4)：636-637
[21]王咏梅,徐继遥和王英鉴,对流层上传重力波的非线性演化[J],地球物理学报,2001,44(2)：154-162.
[22]游景炎.华北冰雹发生条件的合成对比分析.强对流天气文集.气象出版社,1983
[23]李平.中层强风速轴对雹暴形成的作用.强对流天气文集.气象出版社,1983
[24]丁一汇,李鸿洲,章名立等.我国飑线发生条件的研究.大气科学,1982,6(1)：18-27.
[25]李鸿洲,扈忠慈.华北地区的飑线.见：强对流天气文集编辑组,编.强对流天气文集.北京：气象出版社,1983.91-98.
[26]李鸿洲.区域地面天气图上华北飑线的特征及其邻近预报.大气科学,1988,12(1)：42-48.
[27]蔡则怡,李鸿洲,李焕安.华北飑线系统的结构与演变特征.大气科学,1988,12(2)：191199.
[28]李鸿洲,蔡则怡,徐元泰.华北强飑线生成环境与地形作用的数值试验研究.大气科学.1999,23(6)：713-721.
[29]王雷,赵海林,等.2004年7月两次强对流天气过程的对比分析[J].气象,2005,31(11)：65-69.
[2]Brooks, H. E. Dowell C. A. The role of midtroposphric winds in the evolution and maintenance of low-level mesocyclones. Mon. Wea.. Rev.1994,122,126-136
[3]Fovell.R. G.. Numerical simulation of a midlatitude squll line in two dimention.. J. A tmas. Sci.1988,45,3846-3879
[4]Romero, R. Observations and fine grid simulations of a convective outbreak in northeastern Spain:Importance of diurnal forcing and convective cold pools. Monthly weather revies.2001,129(9),2157-2182
[5]Fiuley C. A. Numerial simulation of tornadogenesis in a high-precipitaton supercell Part Ⅰ:Storm evolution and transition into abow echo. Journal of the atmospheric sciences.2001,58(13),1597-1679
[6]Klemp J B. Dynamics of tornadic thunderstorms [J]. Ann. Rev. Fluid Mcch.,1987,19: 369-402.
[7]Rootunno R, Klemp J B, Wcsman M L. A theory for strong, long-lived squall lines [J]. J. Atmos. Sci.,1988,45:463-485.
[8]陶诗言.中国之暴雨[M].北京：气象出版社,1980：1-12.
[9]丁一汇.暴雨和中尺度气象学问题.气象学报,1994,52(3)：274-284.
[10]李耀东.动力和能量参数在强对流天气预报中的应用研究.气象学报,2004,62(4)：401-409.
[11]沈树勤.江苏冰雹强对流天气条件分析及其物理解释.气象,1994,20(9)：25-29.
[12]吴涛,黄锐,舒防国,等.”2003.6.2”十堰强对流天气雷达回波和数值模拟分析.气象科学,2005,25(6)：629-637.
[13]王欢,周军,罗树如,等,强对流活动对对流发展条件影响的数值试验.南京气象学院学报,2005,28(2)：145-152.
[14]于华英,顾松山,刘鹏,等.一次强对流过程的数值模拟.南京气象学院学报,2006,29(3)：305-313.
[15]沈树勤.沿海槽后西北气流冰雹发生条件的对比分析.气象科学,1985,5(1)：18-22.
[16]潘晓滨,陈家华.垂直风切变对风暴云影响的数值模拟.气象科学,1996,16(2)：135-143.
[17]廖玉芳,潘志祥,郭庆.基于单多普勒天气雷达产品的强对流天气预报预警方法.气象科学,2006,26(5)：564：571.
[18]杨晓霞,张爱华,贺业坤。山东省冰雹客观分县预报系统[J].气象,2002,28(10)：41-44.
[19]刘勇.急流次级环流对局地持续强风暴天气的作用[J].气象科技,2005,33(3)：214-217.
[20]寇正等.中尺度对流系统演变中的非线性对流对称不稳定.大气科学,2005,29(4)：636-637
[21]王咏梅,徐继遥和王英鉴,对流层上传重力波的非线性演化[J],地球物理学报,2001,44(2)：154-162.
[22]游景炎.华北冰雹发生条件的合成对比分析.强对流天气文集.气象出版社,1983
[23]李平.中层强风速轴对雹暴形成的作用.强对流天气文集.气象出版社,1983
[24]丁一汇,李鸿洲,章名立等.我国飑线发生条件的研究.大气科学,1982,6(1)：18-27.
[25]李鸿洲,扈忠慈.华北地区的飑线.见：强对流天气文集编辑组,编.强对流天气文集.北京：气象出版社,1983.91-98.
[26]李鸿洲.区域地面天气图上华北飑线的特征及其邻近预报.大气科学,1988,12(1)：42-48.
[27]蔡则怡,李鸿洲,李焕安.华北飑线系统的结构与演变特征.大气科学,1988,12(2)：191199.
[28]李鸿洲,蔡则怡,徐元泰.华北强飑线生成环境与地形作用的数值试验研究.大气科学.1999,23(6)：713-721.
[29]王雷,赵海林,等.2004年7月两次强对流天气过程的对比分析[J].气象,2005,31(11)：65-69.