“03.7”湘西北特大致洪暴雨的触发机制数值研究

叶成志; 潘志祥; 刘志雄; 黄小玉

“03.7”湘西北特大致洪暴雨的触发机制数值研究

1.
兰州大学大气科学学院, 兰州 730000
2.
湖南省气象局, 长沙 410007
3.
娄底市气象台, 娄底 417100

资助项目:

中国气象局武汉暴雨研究所开放基金课题 2004ZD01

国家重点基础研究发展规划项目“我国南方致洪暴雨监测与预测的理论和方法研究”第四课题 2004CB418304

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出版历程
- 收稿日期: 2006-02-28
- 修回日期: 2007-03-02
- 刊出日期: 2007-08-31

Mechanism Triggering the "03.7" Heavy Rainfall in the Northwest of Hunan Province

1.
College of Atmospheic Sciences, Lanzhou University, Lanzhou 730000
2.
Hunan Provincial Meteorological Burean, Changsha 410007
3.
Loudi Meteorological Burean, Loudi 417100

摘要

摘要: 利用常规、地面加密观测资料、GMS卫星云图和常德多普勒天气雷达资料, 结合MM5中尺度数值模式模拟结果对“ 03.7”湘西北特大致洪暴雨过程进行综合分析, 并探讨其可能的触发机制。研究表明: “03.7”湘西北特大暴雨与边界层内多个中尺度辐合扰动的移动和发展密切相关, 且伴随着中尺度雨团的强烈发展, 由此诱发的β-中尺度涡旋是此次特大暴雨过程的直接影响系统; 有组织的多单体风暴活动是张家界这一特大暴雨中心形成的主要原因; 等熵面上的位涡下滑和倾斜涡度的发展可能是导致β-中尺度气旋涡度急剧发展的重要因素; 低空急流扰动、对流层高层强辐散形成的抽吸作用以及湘西北特殊地形对此次暴雨过程有明显的触发和增幅作用。
- 特大致洪暴雨;
- β-中尺度气旋;
- 触发机制
Abstract: The analysis on torrential rain event in Hunan Province on July 7 to 9, 2003 is accomplished.It is the result of the combined use of conventional intensive observational data, GMS satellite cloud picture, Doppler radar data and the numerical simulation result with mesoscale numerical model of the Penn State/NCAR Mesoscale Model 5(MM5). In particular, it emphasizes the output based on the observational facts and the MM5 high resolution data.The mesoscale convective system is discovered which is prone to the existence and maintenance of the heavy rainfall center in Zhangjiajie.In order to reveal the development mechanism and spatial structures of Meiyu front rainstorm mesoscale convective systems, some innovative work about this rainstorm triggering mechanism is done.These important scientific conclusions can be used to seek new forcasting ideas, and ultimately improve the heavy rain forecast.The heavy rain is related to the movement and evolvement of multiple mesoscale convergence disturbances. With the rapid development of the mesoscale rain clusters, the β-mesoscale vortex takes shape, by which this torrential rain is directly affected.The reason of this rainstorm is not the severe multi-cell and super-cell.Due to the atmosphere constantly generation of new convective cells and afterwards vanish in the north, the organized multi-cell storm is the main reason of this heavy rain in Zhangjiajie.The appearance of head wind zone about several kilometers above the district of Zhangjiajie which is reflected in the Doppler radar radial velocity field is the result of small-scale cyclone formation and maintenance. It is closely related to the emergence of continuous heavy rain.In the low troposphere layer, as the Southwest jet velocity fluctuates, jet stream flow and the largest northeast nuclear center are split by it and the development of the β-mesoscale vortex in the northwest of Hunan is triggered.The suction effect caused by the low-level jet disturbance and the divergence on the top-level of troposphere is the triggering mechanism of the heavy rain, and the dynamical and vapor field disturbance induced by the mesoscale topography is the main element of the heavy rain.The β-mesoscale vortex presents intricacy thermal and dynamical structure, the θ_se equiscalar surface tilt is forced by the latent heat release caused by the strong convective movement and the sudden increase of PV on the low-mid level is made.Simultaneous, the strong convective movement takes place in the region of isentropic surface marked by a sunken feature.The PV sliding along the entropy isentropic and the slope vortex development may be the main cause of maintain and development of the β-mesoscale vortex.
- heavy rainfall;
- β-mesoscale vortex;
- triggering mechanism

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图 1 2003年7月8日08:00至9日08:00实况降水量 (a) 与MM5模拟降水量 (b) 的对比 (单位: mm)

Fig. 1 Observation (a) and MM5 simulation (b) of precipitation from 08:00 on July 8 to 08:00 on July 9, 2003 (unit: mm)

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图 2 常德市2003年7月8日21:34至9日00:31多普勒天气雷达0.5°仰角组合反射率因子

(距离圈相距50km)

Fig. 2 The reflectivity observed by Doppler radar located at Changde

(the distance between two adjacent circles is 50 km)

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图 3 2003年7月850 hPa涡度数值模拟图 (单位：10^-5s^-1)

Fig. 3 Simulations of vorticity at 850 hPa in July, 2003(unit:10^-5s^-1)

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图 4 常德市多普勒雷达2003年7月8日21:34至9日00:31 0.5°仰角SRV图

(距离圈相距50km)

Fig. 4 The picture of SRV observed by Doppler radar located at Changde from 21:34 on July 8 to 00:31 on July 9, 2003 with 0.5° elevation

(the distance between two adjacent circles is 50 km)

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图 5 2003年7月9日02:00经过张家界所作地形分析剖面上的风矢量 (矢量) 和沿此剖面的涡度 (等值线, 单位: 10^-5s^-1) 模拟结果垂直分布图

Fig. 5 The section of the wind (vectors) and the vorticity (isolines, unit : 10^-5s^-1) in convective development stageprovided by MM5 mesoscale model along the line crossing Zhangjiajie at 02:00 on July 9, 2003

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图 6 2003年7月8日23:00经过张家界所作地形分析剖面上的风场 (矢量) 和沿此剖面的涡度 (等值线, 单位: 10^-5s^-1) 模拟结果垂直分布图

Fig. 6 The profile of the wind (vectors) and the vorticity (solines, unit: 10^-5s^-1) provided by MM5 mesoscale model crossing Zhangjiajie at 23:00 on July 8, 2003

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图 7 8日23:30常德市多普勒天气雷达4.3°仰角SRV和MM5模式产品叠加图

(距离圈相距50km)(a) 与200 hPa散度叠加 (单位:10^-5s^-1)，(b) 与200 hPa风矢量叠加 (单位：m·s^-1)

Fig. 7 The analysis producet obtained by composite SRV with 4.3° elevation of Changde Dopplar radar and the product of model at 23:30 on July 8, 2003

(the distance between two adjacent circles is 50 km)(a) with 200 hPa divergence overlappled (unit:10^-5s^-1), (b) with 200 hPa wind vectors overlappled (unit:m·s^-1)

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图 8 2003年7月9日02:00经过张家界地区所作的θ_se垂直剖面图 (单位: )

Fig. 8 The cross section (pass Zhangjiajie region) of θ_se provided by MM5 mesoscale model at 02:00 on July 9, 2003(unit:K)

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