两种尺度低涡背景下β中尺度强对流带的演变及成因分析
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摘要
利用WRF中尺度数值模式,NCEP/NCAR再分析资料、多普勒雷达观测资料等,对2015年8月3日发生在山东地区的一次MCS过程进行数值模拟、潜热敏感性试验和对比分析,研究了在两种尺度低涡背景下MCS中β尺度强对流带的发生发展及其成因。结果表明:(1)在天气尺度的东北冷涡槽前,高层有强的高空急流存在,低层有不稳定能量释放为中尺度低涡以及对流发生提供有利背景场,低层低涡发展演变引起MCS的形成,其中伴随着β中尺度强对流带转向、合并以及弓状弯曲和暴雨的加强;(2)低层低涡切变导致多条β中尺度对流带以及小槽出现,当小槽中流场由西风-西南风变为西北风-西南风切变时,β中尺度强对流带发展并伴随小槽转竖,强对流带上南北风的加强是对流带转竖的关键;(3)由涡度方程分析,低层倾侧项对正的垂直涡度贡献最大,倾侧项中,水平涡度在垂直速度的作用下,在强对流区的前部有向正涡度的转换,在对流带合并前这种正涡度可延伸至另一个小槽中,使两个小槽的正涡度区加强合并,小槽和强对流带合并,小槽加深,槽前后南北风分别加大。在强对流带的后部为负涡度区,散度项对负涡度的贡献较大,在对流带合并期间后部散度项引起的负涡度区加大,反气旋扰动加强,导致强对流带出现弓状弯曲;(4)对流强盛前关闭潜热,导致三维风场改变,小槽减弱,扰动场分布散乱,强对流带迅速减弱消失。显见,本次过程中,潜热可引起β中尺度强对流带上小槽迅速加强有利于强对流带转竖。
A MCS process that occurred in Shandong region on August 3, 2015, was investigated and compared with latent heat sensitivity experiments, by the WRF mesoscale numerical model based on NCEP/NCAR reanalysis and doppler radar observation data. The study revealed the evolution and reason of β-mesoscale severe convections in two scales of low vortexes, the results as follows:(1)The upper-level jet stream in front of the trough of the northeast cold vortex and the low-level instability energy release provided favorable background for the lower mesoscale vortex and convection occurrence. The low-level mesoscale vortex development caused the MCS formation, along with turning, merging, and bowing of β-mesoscale severe convections and intensification of the rainstorm.(2) The vortex shear caused emergence of several β-mesoscale convective belts and small troughs, and β-mesoscale convections developed, along with small grooves turning to be vertical, when fields in troughs were changed from the west-southwest wind to the northwest-southwest wind. The strengthening of the south and north wind on the convection is the key to be vertical.(3)It can be seen from the analysis of vorticity equation, that the low-level heeling term contributed the most to vertical vorticity. Horizontal vorticity converted to positive vorticity in the front of severe convective zone, because of vertical velocity influence, and before convections were combined, positive vorticity can be extended to another trough, leading to the mergence and strengthening of positive vorticity areas of two troughs, the mergence of two troughs and convections, the deepening of the trough, and the strengthening of the south and north wind respectively. The divergence term contributed the most to negative vorticity that was mainly in the back of severe convective zone. The increase of negative vorticity zone and the strengthening of anticyclonic disturbance because of the divergence term caused the severe convection to be bowed.(4)Latent heat being closed before the convection became strong, lead to the change of the three-dimensional wind field, the weakening of the trough, the disturbance of the wind and the weakening of the convection. Obviously, latent heat can cause a rapid increase of troughs on mesoscale severe convections, leading to the upright of convective belts.
A MCS process that occurred in Shandong region on August 3, 2015, was investigated and compared with latent heat sensitivity experiments, by the WRF mesoscale numerical model based on NCEP/NCAR reanalysis and doppler radar observation data. The study revealed the evolution and reason of β-mesoscale severe convections in two scales of low vortexes, the results as follows:(1)The upper-level jet stream in front of the trough of the northeast cold vortex and the low-level instability energy release provided favorable background for the lower mesoscale vortex and convection occurrence. The low-level mesoscale vortex development caused the MCS formation, along with turning, merging, and bowing of β-mesoscale severe convections and intensification of the rainstorm.(2) The vortex shear caused emergence of several β-mesoscale convective belts and small troughs, and β-mesoscale convections developed, along with small grooves turning to be vertical, when fields in troughs were changed from the west-southwest wind to the northwest-southwest wind. The strengthening of the south and north wind on the convection is the key to be vertical.(3)It can be seen from the analysis of vorticity equation, that the low-level heeling term contributed the most to vertical vorticity. Horizontal vorticity converted to positive vorticity in the front of severe convective zone, because of vertical velocity influence, and before convections were combined, positive vorticity can be extended to another trough, leading to the mergence and strengthening of positive vorticity areas of two troughs, the mergence of two troughs and convections, the deepening of the trough, and the strengthening of the south and north wind respectively. The divergence term contributed the most to negative vorticity that was mainly in the back of severe convective zone. The increase of negative vorticity zone and the strengthening of anticyclonic disturbance because of the divergence term caused the severe convection to be bowed.(4)Latent heat being closed before the convection became strong, lead to the change of the three-dimensional wind field, the weakening of the trough, the disturbance of the wind and the weakening of the convection. Obviously, latent heat can cause a rapid increase of troughs on mesoscale severe convections, leading to the upright of convective belts.
引文
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[2] 贝耐芳, 赵思雄. 1998二度梅期间突发强暴雨系统的中尺度分析[J]. 大气科学, 2002, 26(4): 526-540.BEI Naifang, ZHAO Sixiong. Mesoscale analysis of severe local heavy rainfall during the second stage of the 1998 Meiyu Season[J]. Chinese Journal of Atmospheric Science, 2002, 26(4): 526-540. (in Chinese)
[3] Houze R A, Smull B F, Dodge P. Mesoscale organization of spring time rainstorms in Oklahoma[J]. Monthly Weather Review, 1990, 118(3): 613-654.
[4] 桌鸿, 赵平, 李春虎, 等. 夏季黄河下游地区中尺度对流系统的气候特征分布[J]. 大气科学, 2012, 36(6): 1112-1122.ZHUO Hong, ZHAO Ping, LI Chunhu, et al. Analysis of climatic characteristics of mesoscale convective system over the lower reaches of the Yellow River during summer[J]. Chinese Journal of Atmospheric Science, 2012, 36(6): 1112-1122. (in Chinese)
[5] 苏爱芳, 孙景兰, 谷秀杰, 等. 河南省对流性暴雨云系特征和概念模型[J]. 应用气象学报, 2013, 24(2): 219-229.SU Aifang, SUN Jinglan, GU Xiujie, et al. Characteristics and conceptual models of convective rainstorm clouds in Henan Province[J]. Journal of Applied Meteorological Science, 2013, 24(2): 219-229. (in Chinese)
[6] 苏爱芳. 黄淮中西部深对流云的演变规律和组织结构[D]. 南京: 南京信息工程大学, 2015.SU Aifang. Evolution and Structure of Deep Convective Clouds in Central and Western Huanghuai Region[D]. Nanjing: Nanjing University of Information Science and Technology, 2015. (in Chinese)
[7] 孙建华, 赵思雄. 华南“94.6”特大暴雨的中尺度对流系统及其环境场研究Ⅱ: 物理过程、 环境场以及地形对中尺度对流系统的作用[J]. 大气科学, 2002, 26(5): 633-646.SUN Jianhua, ZHAO Sixiong. A study of mesoscale convective systems and its environmental fields during the June 1994 record heavy rainfall in south China part Ⅱ: Effect of physical processes, initial enviromental fields and topography on meso-β convective system[J]. Chinese Journal of Atmospheric Science, 2002, 26(5): 633-646. (in Chinese)
[8] 夏茹娣, 赵思雄, 孙建华. 一次华南锋前暖区暴雨β中尺度系统环境特征的分析研究[J]. 大气科学, 2006, 30(5): 988-1008.XIA Rudi, ZHAO Sixiong, SUN Jianhua. A study of circumstances of meso β scale systems of strong heavy rainfall in warm sector ahead of fronts in south China[J]. Chinese Journal of Atmospheric Science, 2006, 30(5): 988-1008. (in Chinese)
[9] 卢焕珍, 张楠, 刘一玮. 天津一次局地大暴雨中尺度对流系统组织化特征与成因[J]. 暴雨灾害, 2015, 34(1): 17-26.LU Huanzhen, ZHANG Nan, LIU Yiwei. Organization characteristic and causal analysis of meso-scale convective system of locally torrential rain in Tianjin[J]. Torrential Rain and Disasters, 2015, 34(1): 17-26. (in Chinese)
[10] 何立富, 陈涛, 周庆亮, 等. 北京“7.10”暴雨β中尺度对流系统分析[J]. 应用气象学报, 2007, 18(5): 655-665.HE Lifu, CHEN Tao, ZHOU Qingliang, et al. The meso-β scale convective system of a heavy rain event on July 10, 2004 in Beijing[J]. Journal of Applied Meteorological Science, 2007, 18(5): 655-665. (in Chinese)
[11] 丁治英, 高松, 常越. MCC转为带状MCSs过程中水平涡度的变化与暴雨的关系[J]. 热带气象学报, 2013, 29(4): 540-550.DING Zhiying, GAO Song, CHANG Yue. Relationship between the variation of horizontal vorticity and heavy rain in the process of MCC turning into banded MCSS[J]. Journal of Tropical Meteorology, 2013, 29(4): 540-550. (in Chinese)
[12] 丁治英, 邢蕊, 徐海明, 等. 多台风的相互作用和水平涡度与垂直涡度的关系[J]. 热带气象学报, 2014, 30(5): 825-835.DING Zhiying, XING Rui, XU Haiming, et al. Interactions of multiple typhoons and relationships of horizontal and vertical vorticity[J]. Journal of Tropical Meteorology, 2014, 30(5): 825-835. (in Chinese)
[13] Davies-Jones R. Streamwise Vorticity: The origin of updraft rotation in supercell storms[J]. Journal of the Atmospheric Sciences, 1984, 41(20): 2991-3006.
[14] Markowski P, Richardson Y, Rasmussen E, et al. Vortex lines within low-level mesocyclones obtained from pseudo-dual-doppler radar observations[J]. Monthly Weather Review, 2008, 136(9): 3513-3535.
[15] Straka J M, Rasmussen E N, Davies-Jones R P, et al. An observational and idealized numerical examination of low-level counter-rotating vortices in the rear flank of supercells[J]. Electronic Journal of Severe Storms Meteorology, 2007, 2(8): 1-22.
[16] 张立祥. 东北冷涡中尺度对流系统研究[D]. 南京:南京信息工程大学, 2008.ZHANG Lixiang. A Study on MCS in Cold Vortex over Northeastern China[D]. Nanjing: Nanjing University of Information Science and Technology, 2008. (in Chinese)
[17] 孙力, 安刚, 廉毅, 等. 夏季东北冷涡持续性活动及其大气环流异常特征的分析[J]. 气象学报, 2000, 58(6): 704-714. SUN Li, AN Gang, LIAN Yi, et al. A study of the persistent activity of northeast cold vortex in summer and its genral circulation anomaly charecteristics[J]. Acta Meteorologica Sinica, 2000, 58(6): 704-714. (in Chinese)
[18] 张立祥, 李泽椿. 东北冷涡研究概述[J]. 气候与环境研究, 2009, 14(2): 218-228.ZHANG Lixiang, LI Zechun. A summary of research on cold vortex over northeast China[J]. Climatic and Environmental Research, 2009, 14(2): 218-228. (in Chinese)
[19] 白人海, 谢安. 东北冷涡过程中的飑线分析[J]. 气象, 1998, 24(4): 37-40.BAI Renhai, XIE An. Analysis of squall lines occurring in cold vortexes over northeast China[J]. Meteorology, 1998, 24(4): 37-40. (in Chinese)
[20] 胡伯威, 潘鄂芬. 梅雨期长江流域两类气旋性扰动和暴雨[J]. 应用气象学报, 1996, 7(2): 138-144.HU Buowei, PAN Efen. Two kinds of cyclonic disturbances and their accompanied heavy rain in the Yangtze River Valley during the Mei-Yu period[J]. Journal of Applied Meteorological Science, 1996, 7(2): 138-144. (in Chinese)
[21] 程麟生, 冯伍虎. “98.7”突发大暴雨及中尺度低涡结构的分析和数值模拟[J]. 大气科学, 2001, 25(4): 465-478.CHENG Linsheng, FENG Wuhu. Analyses and numerical simulation on an abrupt heavy rainfall and structure of a mesoscale vortex during July 1998[J]. Chinese Journal of Atmospheric Science, 2001, 25(4): 465-478. (in Chinese)
[22] 孙建华, 张小玲, 齐琳琳, 等. 2002年中国暴雨试验期间一次低涡切变上发生发展的中尺度对流系统研究[J]. 大气科学, 2004, 28(5): 675-691.SUN Jianhua, ZHANG Xiaoling, QI Linlin, et al. A study of vortex and its mesoscale convective system during China heavy rainfall experiment and study in 2002[J]. Chinese Journal of Atmospheric Science, 2004, 28(5): 675-691. (in Chinese)
[23] 徐亚梅, 高坤. 1998年7月22日长江中游中β尺度低涡的数值模拟及分析[J]. 气象学报, 2002, 60(1): 85-95.XU Yamei, GAO Kun. Simulation and analysis of meso-β vortex over middle reaches of the Yangtse River on 22 July 1998[J]. Acta Meteorologica Sinica, 2002, 60(1): 85-95. (in Chinese)
[24] 王智, 翟国庆, 高坤. 长江中游一次β中尺度低涡的数值模拟[J]. 气象学报, 2003, 60(1): 66-77.WANG Zhi, ZHAI Guoqing, GAO Kun. Analysis and numerical simulation of a meso-β-scale vortex in the middle reaches of the Yangtze River[J]. Acta Meteorologica Sinica, 2003, 60(1): 66-77. (in Chinese)
[2] 贝耐芳, 赵思雄. 1998二度梅期间突发强暴雨系统的中尺度分析[J]. 大气科学, 2002, 26(4): 526-540.BEI Naifang, ZHAO Sixiong. Mesoscale analysis of severe local heavy rainfall during the second stage of the 1998 Meiyu Season[J]. Chinese Journal of Atmospheric Science, 2002, 26(4): 526-540. (in Chinese)
[3] Houze R A, Smull B F, Dodge P. Mesoscale organization of spring time rainstorms in Oklahoma[J]. Monthly Weather Review, 1990, 118(3): 613-654.
[4] 桌鸿, 赵平, 李春虎, 等. 夏季黄河下游地区中尺度对流系统的气候特征分布[J]. 大气科学, 2012, 36(6): 1112-1122.ZHUO Hong, ZHAO Ping, LI Chunhu, et al. Analysis of climatic characteristics of mesoscale convective system over the lower reaches of the Yellow River during summer[J]. Chinese Journal of Atmospheric Science, 2012, 36(6): 1112-1122. (in Chinese)
[5] 苏爱芳, 孙景兰, 谷秀杰, 等. 河南省对流性暴雨云系特征和概念模型[J]. 应用气象学报, 2013, 24(2): 219-229.SU Aifang, SUN Jinglan, GU Xiujie, et al. Characteristics and conceptual models of convective rainstorm clouds in Henan Province[J]. Journal of Applied Meteorological Science, 2013, 24(2): 219-229. (in Chinese)
[6] 苏爱芳. 黄淮中西部深对流云的演变规律和组织结构[D]. 南京: 南京信息工程大学, 2015.SU Aifang. Evolution and Structure of Deep Convective Clouds in Central and Western Huanghuai Region[D]. Nanjing: Nanjing University of Information Science and Technology, 2015. (in Chinese)
[7] 孙建华, 赵思雄. 华南“94.6”特大暴雨的中尺度对流系统及其环境场研究Ⅱ: 物理过程、 环境场以及地形对中尺度对流系统的作用[J]. 大气科学, 2002, 26(5): 633-646.SUN Jianhua, ZHAO Sixiong. A study of mesoscale convective systems and its environmental fields during the June 1994 record heavy rainfall in south China part Ⅱ: Effect of physical processes, initial enviromental fields and topography on meso-β convective system[J]. Chinese Journal of Atmospheric Science, 2002, 26(5): 633-646. (in Chinese)
[8] 夏茹娣, 赵思雄, 孙建华. 一次华南锋前暖区暴雨β中尺度系统环境特征的分析研究[J]. 大气科学, 2006, 30(5): 988-1008.XIA Rudi, ZHAO Sixiong, SUN Jianhua. A study of circumstances of meso β scale systems of strong heavy rainfall in warm sector ahead of fronts in south China[J]. Chinese Journal of Atmospheric Science, 2006, 30(5): 988-1008. (in Chinese)
[9] 卢焕珍, 张楠, 刘一玮. 天津一次局地大暴雨中尺度对流系统组织化特征与成因[J]. 暴雨灾害, 2015, 34(1): 17-26.LU Huanzhen, ZHANG Nan, LIU Yiwei. Organization characteristic and causal analysis of meso-scale convective system of locally torrential rain in Tianjin[J]. Torrential Rain and Disasters, 2015, 34(1): 17-26. (in Chinese)
[10] 何立富, 陈涛, 周庆亮, 等. 北京“7.10”暴雨β中尺度对流系统分析[J]. 应用气象学报, 2007, 18(5): 655-665.HE Lifu, CHEN Tao, ZHOU Qingliang, et al. The meso-β scale convective system of a heavy rain event on July 10, 2004 in Beijing[J]. Journal of Applied Meteorological Science, 2007, 18(5): 655-665. (in Chinese)
[11] 丁治英, 高松, 常越. MCC转为带状MCSs过程中水平涡度的变化与暴雨的关系[J]. 热带气象学报, 2013, 29(4): 540-550.DING Zhiying, GAO Song, CHANG Yue. Relationship between the variation of horizontal vorticity and heavy rain in the process of MCC turning into banded MCSS[J]. Journal of Tropical Meteorology, 2013, 29(4): 540-550. (in Chinese)
[12] 丁治英, 邢蕊, 徐海明, 等. 多台风的相互作用和水平涡度与垂直涡度的关系[J]. 热带气象学报, 2014, 30(5): 825-835.DING Zhiying, XING Rui, XU Haiming, et al. Interactions of multiple typhoons and relationships of horizontal and vertical vorticity[J]. Journal of Tropical Meteorology, 2014, 30(5): 825-835. (in Chinese)
[13] Davies-Jones R. Streamwise Vorticity: The origin of updraft rotation in supercell storms[J]. Journal of the Atmospheric Sciences, 1984, 41(20): 2991-3006.
[14] Markowski P, Richardson Y, Rasmussen E, et al. Vortex lines within low-level mesocyclones obtained from pseudo-dual-doppler radar observations[J]. Monthly Weather Review, 2008, 136(9): 3513-3535.
[15] Straka J M, Rasmussen E N, Davies-Jones R P, et al. An observational and idealized numerical examination of low-level counter-rotating vortices in the rear flank of supercells[J]. Electronic Journal of Severe Storms Meteorology, 2007, 2(8): 1-22.
[16] 张立祥. 东北冷涡中尺度对流系统研究[D]. 南京:南京信息工程大学, 2008.ZHANG Lixiang. A Study on MCS in Cold Vortex over Northeastern China[D]. Nanjing: Nanjing University of Information Science and Technology, 2008. (in Chinese)
[17] 孙力, 安刚, 廉毅, 等. 夏季东北冷涡持续性活动及其大气环流异常特征的分析[J]. 气象学报, 2000, 58(6): 704-714. SUN Li, AN Gang, LIAN Yi, et al. A study of the persistent activity of northeast cold vortex in summer and its genral circulation anomaly charecteristics[J]. Acta Meteorologica Sinica, 2000, 58(6): 704-714. (in Chinese)
[18] 张立祥, 李泽椿. 东北冷涡研究概述[J]. 气候与环境研究, 2009, 14(2): 218-228.ZHANG Lixiang, LI Zechun. A summary of research on cold vortex over northeast China[J]. Climatic and Environmental Research, 2009, 14(2): 218-228. (in Chinese)
[19] 白人海, 谢安. 东北冷涡过程中的飑线分析[J]. 气象, 1998, 24(4): 37-40.BAI Renhai, XIE An. Analysis of squall lines occurring in cold vortexes over northeast China[J]. Meteorology, 1998, 24(4): 37-40. (in Chinese)
[20] 胡伯威, 潘鄂芬. 梅雨期长江流域两类气旋性扰动和暴雨[J]. 应用气象学报, 1996, 7(2): 138-144.HU Buowei, PAN Efen. Two kinds of cyclonic disturbances and their accompanied heavy rain in the Yangtze River Valley during the Mei-Yu period[J]. Journal of Applied Meteorological Science, 1996, 7(2): 138-144. (in Chinese)
[21] 程麟生, 冯伍虎. “98.7”突发大暴雨及中尺度低涡结构的分析和数值模拟[J]. 大气科学, 2001, 25(4): 465-478.CHENG Linsheng, FENG Wuhu. Analyses and numerical simulation on an abrupt heavy rainfall and structure of a mesoscale vortex during July 1998[J]. Chinese Journal of Atmospheric Science, 2001, 25(4): 465-478. (in Chinese)
[22] 孙建华, 张小玲, 齐琳琳, 等. 2002年中国暴雨试验期间一次低涡切变上发生发展的中尺度对流系统研究[J]. 大气科学, 2004, 28(5): 675-691.SUN Jianhua, ZHANG Xiaoling, QI Linlin, et al. A study of vortex and its mesoscale convective system during China heavy rainfall experiment and study in 2002[J]. Chinese Journal of Atmospheric Science, 2004, 28(5): 675-691. (in Chinese)
[23] 徐亚梅, 高坤. 1998年7月22日长江中游中β尺度低涡的数值模拟及分析[J]. 气象学报, 2002, 60(1): 85-95.XU Yamei, GAO Kun. Simulation and analysis of meso-β vortex over middle reaches of the Yangtse River on 22 July 1998[J]. Acta Meteorologica Sinica, 2002, 60(1): 85-95. (in Chinese)
[24] 王智, 翟国庆, 高坤. 长江中游一次β中尺度低涡的数值模拟[J]. 气象学报, 2003, 60(1): 66-77.WANG Zhi, ZHAI Guoqing, GAO Kun. Analysis and numerical simulation of a meso-β-scale vortex in the middle reaches of the Yangtze River[J]. Acta Meteorologica Sinica, 2003, 60(1): 66-77. (in Chinese)