一次西南地区暴雨的诊断分析和数值模拟
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摘要
本文利用气象常规资料、NCEP/NCAR1°×1°再分析资料以及地面站逐日降水资料对2009年7月31日至8月1日发生在我国四川省的一次暴雨过程进行天气诊断分析。采用NCEP再分析资料以及中尺度滤波技术,并且利用中尺度数值模式WRF对这次降水过程进行模拟,利用数值模拟输出的较密的时空资料探讨这次降水过程的发生发展的特征和机理。天气分析表明,此次暴雨过程中500hPa高纬度环流形势为两槽两脊型,即我国新疆地区和蒙古交界区和东亚地区为低压槽,新疆北部地区和蒙古东部是高压脊；在西藏上空存在一个闭合的小低压,副高内的东南风带来大量的水汽,随着西藏上空的低涡东移,副高脊线西侧变形为东北西南走向,四川东部为较强的西南气流控制。通过对这次暴雨过程的诊断分析和模式模拟可以发现：散度场、水汽通量和水汽通量散度对暴雨落区具有较好的指示作用,充沛的水汽为暴雨的发生与发展提供了条件,低层水汽辐合是暴雨水汽的主要来源；高空辐散、低空辐合的散度场配置有利于对流运动的发展,此外水汽的汇合主要也是由于低空流场的辐合作用。湿位涡的正压项与斜压项综合反映了暴雨区对流不稳定和斜压不稳定状况；高层的位涡高值下传,高值位涡的干冷空气加强了低层的扰动,降低了低层的稳定度,迫使中低层暖空气抬升,促使对流不稳定能量与潜热能的释放,促进了暴雨的发展。垂直风切变使得平均气流动能转化为扰动动能,激发了重力波的产生,重力波通过发展的积雨云时,加大云内的上升速度,使得不稳定能量得到释放,从而产生降水。强降水区域上空存在辐合辐散的链式分布,表示了重力波的存在。辐合辐散区域开始形成于川西高原下山坡处,并且逐渐往东移动,值的大小也在逐渐减弱,重力波对这次降水过程强度的影响是成正比的。辐散辐合区域相应地对应着垂直运动强烈的区域,气流的上升运动随重力波的发展愈加强烈,使得对流运动得以发展。随后重力波继续东移减弱,直至最后消亡。高空急流出口区附近的非地转平衡流引发的地转适应过程在中尺度重力波的发生和发展过程中也起了十分重要的作用；高空急流出口区附近中尺度重力波是在地转调整以及切变不稳定的过程中产生发展的,从地转调整和切变不稳定的产生顺序来看,地转调整提前于切变不稳定的产生。因此,我们可以认为非线性平衡方程对于降水带的移动具有预判的作用,而理查森数则与降水则具有同时性特征。另外这次强降水过程中,波动基本满足Lindzen等的波导条件,但是从前文的分析中看到重力波在东移的过程中在逐渐减弱,并最终消亡。7月31日的重力波的存在以及其后的发展对暴雨的影响是比较显著的,但是到了8月1日对流对暴雨的发展起到了主要的影响作用,重力波在这时不再对暴雨产生影响。
A heavy rain storm which happened in Sichuan province from July 31 to August 1 2009 is analyzed by using regular meteorological data, NCEP/NCAR 1°×1°reanalysis data and daily ground station precipitation data. By using the NCEP reanalysis data and mesoscale filter technology and the model output with high spatial and temporal resolution, the mechanism and characteristic of the process of this heavy rain can be studied in detail. Synoptic analysis showed that during this heavy rain 500hPa circumpolar latitude circulation took the pattern of typical two-trough and two-ridge. There was a closure trough high up in the air of Tibet. The southeast winds in the subtropical high pressure belt brought a lot of water vapor. The eastern Sichuan was controlled by the stronger southwestern airflow. Through the diagnostic analysis and model simulation of this heavy rainfall can be found that Divergence field, water vapor flux and water vapor flux divergence had good indication on the rainfall. Rich water vapor provided the condition of the occurrence and development of the rain storm. The convergence of water vapor in the lower level was the main source of the rain storm. Divergence in the upper level while convergence in the lower level was conducive to the development of the development of convection, additionally, the convergence of water vapor was mainly due to the convergence of flow in the lower level. The barotropic term and baroclinic term of MPV comprehensively reflected the convective instability and baroclinic instability of rain storm zone. High value PV in the high level downloaded and the dry cold air of high value PV enhanced the disturbance in the lower level, forcing the elevation of the warm air in the lower level, promoting the release of convective unstable energy and latent heat and the development of heavy rain. Vertical wind shear made the mean flow kinetic energy into eddy kinetic energy, stimulating the generation of gravity waves. When gravity waves passed through developmental cumulonimbus, increasing the ascent speed in the cloud, making the instability released, thereby produced precipitation. There were distribution chains of convergence and divergence existing over the region of heavy rain which indicated the existence of gravity waves. The convergence and divergence zone began to form in the slope at west Sichuan plateau and gradually moved eastward, whose value was gradually decreased. The affect of gravity waves to this precipitation process was proportional. The convergence and divergence zone corresponded to the strong vertical movement region and with the development of gravity waves the increasing of flow was more strongly, which made to the development of convection. Then gravity waves continue moved eastward and reduced gradually until the final demise. The geostrophic adjustment process inducing by unbalanced flow near the exit area of the jet stream in the upper level also played a very important role in the occurrence and development of mesoscale gravity waves. The gravity waves near the exit area of the jet stream in the upper level were induced by the process of geostrophic and shear instability. Form the generation order of geostrophic adjustment and shear instability, geostrophic adjustment was advanced to shear instability. Therefore, we can consider that nonlinear balance equation could predict the movement of precipitation while the Richardson number had the simultaneous characteristic with precipitation. Additionally, during this heavy rainfall, fluctuations basically met the waveguide conditions of Lindzen, etc. however, in the analysis of the previous text the gravity waves continue moved eastward and reduced gradually until the final demise. The existence of gravity waves in July 31 and the subsequent development had significant affect on rain storm but when it came to August 1 convection played a major role in the development of rain storm and gravity waves were no longer affecting on rain storm.
A heavy rain storm which happened in Sichuan province from July 31 to August 1 2009 is analyzed by using regular meteorological data, NCEP/NCAR 1°×1°reanalysis data and daily ground station precipitation data. By using the NCEP reanalysis data and mesoscale filter technology and the model output with high spatial and temporal resolution, the mechanism and characteristic of the process of this heavy rain can be studied in detail. Synoptic analysis showed that during this heavy rain 500hPa circumpolar latitude circulation took the pattern of typical two-trough and two-ridge. There was a closure trough high up in the air of Tibet. The southeast winds in the subtropical high pressure belt brought a lot of water vapor. The eastern Sichuan was controlled by the stronger southwestern airflow. Through the diagnostic analysis and model simulation of this heavy rainfall can be found that Divergence field, water vapor flux and water vapor flux divergence had good indication on the rainfall. Rich water vapor provided the condition of the occurrence and development of the rain storm. The convergence of water vapor in the lower level was the main source of the rain storm. Divergence in the upper level while convergence in the lower level was conducive to the development of the development of convection, additionally, the convergence of water vapor was mainly due to the convergence of flow in the lower level. The barotropic term and baroclinic term of MPV comprehensively reflected the convective instability and baroclinic instability of rain storm zone. High value PV in the high level downloaded and the dry cold air of high value PV enhanced the disturbance in the lower level, forcing the elevation of the warm air in the lower level, promoting the release of convective unstable energy and latent heat and the development of heavy rain. Vertical wind shear made the mean flow kinetic energy into eddy kinetic energy, stimulating the generation of gravity waves. When gravity waves passed through developmental cumulonimbus, increasing the ascent speed in the cloud, making the instability released, thereby produced precipitation. There were distribution chains of convergence and divergence existing over the region of heavy rain which indicated the existence of gravity waves. The convergence and divergence zone began to form in the slope at west Sichuan plateau and gradually moved eastward, whose value was gradually decreased. The affect of gravity waves to this precipitation process was proportional. The convergence and divergence zone corresponded to the strong vertical movement region and with the development of gravity waves the increasing of flow was more strongly, which made to the development of convection. Then gravity waves continue moved eastward and reduced gradually until the final demise. The geostrophic adjustment process inducing by unbalanced flow near the exit area of the jet stream in the upper level also played a very important role in the occurrence and development of mesoscale gravity waves. The gravity waves near the exit area of the jet stream in the upper level were induced by the process of geostrophic and shear instability. Form the generation order of geostrophic adjustment and shear instability, geostrophic adjustment was advanced to shear instability. Therefore, we can consider that nonlinear balance equation could predict the movement of precipitation while the Richardson number had the simultaneous characteristic with precipitation. Additionally, during this heavy rainfall, fluctuations basically met the waveguide conditions of Lindzen, etc. however, in the analysis of the previous text the gravity waves continue moved eastward and reduced gradually until the final demise. The existence of gravity waves in July 31 and the subsequent development had significant affect on rain storm but when it came to August 1 convection played a major role in the development of rain storm and gravity waves were no longer affecting on rain storm.
引文
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[23]张芳华,马旭林.2003年6月24-25日江南特大暴雨数值模拟和诊断分析[J].气象,2004,30(1)：28-32.
[24]周毅,侯志明,刘宇迪.数值天气预报基础[M].北京：气象出版社,2003：164-165.
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[30]李麦村.飑线形成的非线性过程[J].中国科学,1976,6：592～601.
[31]李麦村.重力波对特大暴雨的触发作用[J].大气科学,1978,3：201～209.
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[34]寿绍文,李耀辉,范可.暴雨中尺度气旋发展的等熵面位涡分析[J].气象学报,2001,59(6)：560-568.
[35]章国材.美国WRF模式的进展和应用前景[J].气象,2004,30(8)：27-31.
[36]J. Michalakes, J.et al., Development of a next-generation regional weather research and forecast model, Argonne National Laboratory preprint[J],2001, ANL/MCS-P868-0101, pp.8.
[37]Michalakes, J., J.Dudhia, D. Gill, J. Klemp and W. Skamarock. Design of a next-generation regional weather re-search and forecast model Towards Teracomputing[j]. World Scientific, River Edge, New Jersey,1999,117-124.
[38]邓莲堂,王建捷.新一代中尺度天气预报模式-WRF模式简介.奥运气象保障技术研究,2004,68-75.
[39]闺之辉,邓莲堂.微物理过程优选及其个例预报试验.奥运气象保障技术研究,2004, 84-89.
[40]纪晓玲,胡文东,马筛艳等.蒙古冷涡影响下宁夏两次典型冰雹天气对比分析[J].自然灾害学报,2008,17(2)：103-109
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[2]缪强.青藏高原天气系统与背风坡浅薄天气系统耦合相互作用的特征分析[J].四川气象,1999,19(3)：18-22.
[3]陈忠明,闵文彬,缪强,等.高原涡与西南涡耦合作用的个例诊断[J].高原气象,2004,23(1)：76-80.
[4]丁治英.西南涡动态的合成诊断[J].高原气象,1988,10,2,156-165.
[5]Kou Y. H, Cheng L S, and Anthes R A. Mesoscale analysis of the Sichuan flood catastrophe, 11-15 July 1981. Mon. Wea. Rev.,1986,114(11):1984-2003.
[6]陈忠明.四川盆地西南涡形成的天气动力学模型[J].低纬高原天气,1991,4：47-54,
[7]寿绍文,励申申,姚秀萍.中尺度气象学[M].北京：气象出版社,2003.
[8]Koch S E, Dorian P B. A mesoscale gravity wave event observed during CCOPE. Part III: Wave environment and probable source mechanisms. Mon. Wea. Rev.,1988,116 (12): 2570～2592.
[9]Zhang D., Fritsch J M. Numerical simulation of the mesoscale structure and evolution of the 1977 Johnstown flood. Part III:Internal gravity and squall line. J. Atmos. Sci.,1988,45 (7): 1252～1268.
[10]Stobie J G, Einaudi F, Uccellini L W. A case study of gravity waves covective storms interaction,9 May 1979 [J]. J. Atmos. Sci.,1983,40:2804～2830.
[11]Uccellini L W, Koch S E. The synoptic setting and possibl energy sources for mesoscale wave disturbances. Mon. Wea. Rew.,1987,115 (3):721～729.
[12]许小锋,孙照渤.非地转平衡流激发的重力惯性波对梅雨锋暴雨影响的动力学研究[J].气象学报,2003,61(6)：655-660
[13]Miles J W. on the stability of heterogeneous shear flows. J. Fluid Mech.,1961,10: 496～508.
[14]Howard L N. Note on paper of John W. Miles. J. Fluid Mech.,1961,10:509～512.
[15]Ferreti, R., F. Einaudi, and L. W. Uccellini,1988:Wave disturbances associated with the Red River Valley severe weather outbreak of 10-11 April 1979. Meteor. Atmos. Phys.,39, 132-168.
[16]Schneider, R. S., Large-amplitude gravity wave disturbances within the intense Midwest extratropical cyclone of 15 December 1987[J]. Wea. Forecasting,1990,5,533-558.
[17]Powers, J. G., and R. J. Reed, Numerical simulation of the large-amplitude mesoscale gravity wave of 15 December 1987 in the central United States[J]. Mon. Wea. Rev.,1993, 121,2285-2308.
[18]Pokrandt, P. J., G. J. Tripoli, and D. D. Houghton, Processes leading to the formation of mesoscale waves in the Midwest cyclone of 15 December 1987[J]. Mon. Wea. Rev.,1996, 124,2726-2752.
[19]朱利华,周伟灿,邹兰军.垂直切变流中非线性重力波及其相互作用[J].南京气象学院学报,2004,27(3)：405-412.
[20]龚佃利,吴增茂,傅刚.一次华北强对流风暴的中尺度特征分析[J].大气科学,2005,29(3),453-464.
[21]郑祚芳,沈桐立.自适应网络模式在暴雨数值模拟中的应用[J].南京气象学院学报,2002,25(2)：173-179.
[22]王健,寿绍文,陈力强.“03.8”辽宁地区暴雨过程成因的诊断分析[J].气象,2004,31(4)：18-22.
[23]张芳华,马旭林.2003年6月24-25日江南特大暴雨数值模拟和诊断分析[J].气象,2004,30(1)：28-32.
[24]周毅,侯志明,刘宇迪.数值天气预报基础[M].北京：气象出版社,2003：164-165.
[25]Rossby, C.-G.. Planetary flow patterns in the atmosphere. Quart. J. Roy. Meteor. Soc.1940, 66,68-87.
[26]Zhang F, Koch S E, Davis C A, et al A survey of unbalanced flow diagnostics and their application[J].Adv Atmos Sci2000,17(2):165-173.
[27]Zhang F, Koch S E, Davis C A, et al Wavelet analysis and the governing dynamics of a large amplitude mesoscale gravity wave event along the East Coast of the United States[J].Quart J Roy Meteor Soc,2001,127(577):2209-2245.
[28]Zhang F, Koch S E. Numerical simulations of a gravity wave event over CCOPE. Part Ⅱ: Waves generated by an orographic density current[J].MonWeaRev,2000,128(8):2777-2796.
[29]华北暴雨编写组.华北暴雨[M].北京：气象出版社,1992：162-163.
[30]李麦村.飑线形成的非线性过程[J].中国科学,1976,6：592～601.
[31]李麦村.重力波对特大暴雨的触发作用[J].大气科学,1978,3：201～209.
[32]丁德刚,王树芬.相向而行的重力波与暴雨[J].大气科学,1994,7：451-455.
[33]Hoskins B J, McIntyre M. E, Robertson A. W.. On the use significance of isentropic potential vorticity maps[J]. Quart. J. R. Meteor. Soc,1985,111:877-946.
[34]寿绍文,李耀辉,范可.暴雨中尺度气旋发展的等熵面位涡分析[J].气象学报,2001,59(6)：560-568.
[35]章国材.美国WRF模式的进展和应用前景[J].气象,2004,30(8)：27-31.
[36]J. Michalakes, J.et al., Development of a next-generation regional weather research and forecast model, Argonne National Laboratory preprint[J],2001, ANL/MCS-P868-0101, pp.8.
[37]Michalakes, J., J.Dudhia, D. Gill, J. Klemp and W. Skamarock. Design of a next-generation regional weather re-search and forecast model Towards Teracomputing[j]. World Scientific, River Edge, New Jersey,1999,117-124.
[38]邓莲堂,王建捷.新一代中尺度天气预报模式-WRF模式简介.奥运气象保障技术研究,2004,68-75.
[39]闺之辉,邓莲堂.微物理过程优选及其个例预报试验.奥运气象保障技术研究,2004, 84-89.
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