Study on circulation characteristics and water vapor anomaly of extreme rainstorm events in Shanxi Province

doi:10.11755/j.issn.1006-7639(2024)-03-0426

Abstract

Abstract:

Study on the regularity of extreme rainstorm in Shanxi Province is of great significance for carrying out forecast and warning and disaster prevention. Based on the conventional observation data and the fifth generation atmospheric reanalysis (ERA5) from European Centre for Medium-Range Weather Forecasts (ECMWF), the climatic characteristics, circulation impact systems, and water vapor anomaly characteristics were studied about 17 extreme rainstorm events in Shanxi Province from June to September during 1981-2018 by using circulation analysis and physical quantity diagnostics methods, along with using standardized anomaly as abnormal degree. The results show that extreme rainstorms in Shanxi Province mainly occurred in July and August, the rainstorm areas were mainly located in the central and southern parts, extreme rainstorms have occurred more frequently since 2010. The main impact systems were 700 hPa low vortex and typhoon system, and there were two water vapor channels from south and east. The moisture in the lower layers were significantly high during extreme rainstorms, for the maximum value of mean specific humidity on rainstorm area during extreme rainstorm process, most cases exceeded 14.2 g·kg^-1 on 850 hPa, and exceeded 9.8 g·kg^-1 on 700 hPa, which corresponding average abnormal degree on rainstorm areas exceeded 1.6. The extreme of water vapor was prominent in the vapor flux convergence center in the lower layers, the mean abnormal degree for the maximum values of the vapor flux convergence center during the process over rainstorm areas on 700, 850 hPa for 17 extreme rainstorms were -8, -6, respectively, wherein, the maximum abnormal degree of vapor flux convergence center on 850 hPa under the extreme rainstorm influenced by weakened typhoon low pressure could up to -12. Based on above circulation and water vapor characteristics, the conceptual models of extreme rainstorm are established, the forecasting reference indexes of moisture content and vapor flux convergence intensity on low layers are given.

Key words: extreme rainstorm, circulation characteristics, water vapor anomaly, forecasting index

摘要：

研究山西极端暴雨发生规律对开展预报预警、灾害防御具有重要意义。本文利用常规观测资料和欧洲中期天气预报中心（European Centre for Medium-Range Weather Forecasts，ECMWF）第五代大气再分析资料（ERA5），采用标准化距平作为异常度，运用环流分析和物理量诊断等方法，研究1981—2018年6—9月山西17次极端暴雨的气候特征、环流影响系统和水汽异常特征。结果表明：山西极端暴雨主要出现在7—8月，暴雨区主要位于中南部，2010年以来极端暴雨明显多发；影响系统主要是700 hPa低涡和台风系统，有偏南和偏东两支水汽通道。极端暴雨过程中，低层水汽含量明显偏高，从暴雨区平均比湿的过程最大值看，大部分过程850 hPa超过14.2 g·kg^-1，700 hPa则可超过9.8 g·kg^-1、对应暴雨区平均异常度达1.6 以上；水汽的极端性在低层水汽通量辐合中心表现突出，17次极端暴雨700、850 hPa暴雨区水汽通量辐合中心过程最大值的异常度均值分别达-8、-6，其中台风减弱低压影响下的极端暴雨850 hPa水汽通量辐合中心最大异常度达-12。根据以上环流和水汽特征建立极端暴雨概念模型，并给出极端暴雨低层水汽含量和水汽通量辐合强度预报参考指标。

关键词: 极端暴雨, 环流特征, 水汽异常, 预报指标

CLC Number:

P458.121.1

ZHOU Jinhong, WANG Xiuming, TIAN Xiaoting, ZHANG Zexiu, LI Shuwen, CAI Xiaofang. Study on circulation characteristics and water vapor anomaly of extreme rainstorm events in Shanxi Province[J]. Journal of Arid Meteorology, 2024, 42(3): 426-436.

周晋红, 王秀明, 田晓婷, 张泽秀, 李树文, 蔡晓芳. 山西极端暴雨环流特征及水汽异常研究[J]. 干旱气象, 2024, 42(3): 426-436.

Figures/Tables 12

Tab.1 Statistics of the extreme rainstorm events in Shanxi Province from June to September during 1981-2018

序号	时段	日期	≥50 mm站数	≥100 mm站数	暴雨中心降水量/ mm	暴雨中心站点	本站暴雨中心降水量排位
1	20：00—20：00	1981-08-15	27	13	187.5	永和	1
2	20：00—20：00	1982-07-30	17	4	207.0	垣曲	3
3	20：00—20：00	1989-08-16	30	5	151.7	沁源	2
4	20：00—20：00	1992-08-31	23	6	160.0	汾西	1
5	20：00—20：00	1993-08-4	29	6	131.6	灵石	1
6	20：00—20：00	1996-07-31	13	5	178.8	安泽	1
7	20：00—20：00	1996-08-04	27	6	163.8	和顺	1
8	20：00—20：00	2001-07-27	49	8	127.9	黎城	1
9	20：00—20：00	2003-08-26	29	12	117.3	安泽	5
10	20：00—20：00	2005-09-20	39	5	165.5	安泽	2
11	08：00—08：00	2007-07-29	24	4	313.3	垣曲	1
12	08：00—08：00	2011-07-02	27	6	141.0	绛县	1
13	20：00—20：00	2012-07-21	19	5	126.4	偏关	1
14	20：00—20：00	2012-07-31	37	3	221.2	晋城	1
15	20：00—20：00	2013-07-10	16	5	158.4	阳城	1
16	08：00—08：00	2016-07-08	18	6	169.3	交口	2
17	08：00—08：00	2016-07-19	39	10	223.3	阳泉	1

Fig.1 The distribution of rainstorm stations frequency （solid lines， Unit： times） with daily precipitation equal to and more than 50 mm and rainstorm center stations （red dots） of 17 extreme rainstorm processes in Shanxi Province from June to September during 1981-2018 （The color shaded is terrain height，Unit： m）

Fig.2 The occurrence time of 17 extreme rainstorms and the duration of corresponding rainstorm processes in Shanxi Province from June to September during 1981-2018

Fig.3 Circulation composite field during the occurrence of 700 hPa low vortex pattern extreme rainstorms (black solid lines represent average geopotential height on 500 hPa, Unit: dagpm; arrow vectors and color shaded represent 700 hPa average wind field and wind speed, respectively, Unit: m·s-1) (a), 500 hPa geopotential height field (black solid lines, Unit: dagpm), 700 hPa wind field (arrow vectors) and wind speed (color shaded) (Unit: m·s-1), the area of wind speed greater than or equal to 40 m·s-1 on 200 hPa (purple solid lines, Unit: m·s-1) at 08:00 on 21 July 2012 (b), the spatial distribution of precipitation (Unit: mm) in Shanxi Province from 20:00 on 20 to 20:00 on 21 July 2012 (c) (The red solid line area is Shanxi Province. the same as below)

Fig.4 Circulation composite field during the extreme rainstorms of interaction pattern between westerly low trough (vortex) and typhoon (black solid lines represent average geopotential height on 500 hPa, Unit: dagpm; arrow vectors and color shaded represent 700 hPa average wind field and wind speed, respectively, Unit: m·s-1) (a), 500 hPa geopotential height field (black solid lines, Unit: dagpm), 700 hPa wind field (arrow vectors) and wind speed (color shaded) (Unit: m·s-1) at 08:00 on 31 August 1992 (b), the spatial distribution of precipitation (Unit: mm) in Shanxi Province from 20:00 on 30 to 20:00 on 31 August 1992 (c)

Fig.5 The 500 hPa geopotential height field (black solid lines, Unit: dagpm), wind field (arrow vectors) and wind speed (color shaded) (Unit: m·s-1) on 700 hPa at 20:00 on 19 July 2016 (a), the spatial distribution of precipitation (Unit: mm) in Shanxi Province from 08:00 on 19 to 08:00 on 20 July 2016 (b)

Fig.6 The 500 hPa geopotential height field (black solid lines, Unit: dagpm), wind field (arrow vectors) and wind speed (color shaded) (Unit: m·s-1) on 700 hPa at 08:00 on 4 August 1996 (a), the spatial distribution of precipitation (Unit: mm) in Shanxi Province from 20:00 on 3 to 20:00 on 4 August 1996 (b)

Fig.7 The composite fields of vertical integrated vapor flux from the ground to 300 hPa (arrows and shaded, Unit: kg·m-1·s-1) during extreme rainstorms of 700 hPa low vortex pattern (a) and interaction pattern between westerly low trough (vortex) and typhoon (b), the vertical integrated vapor flux from the ground to 300 hPa (arrows and shaded, Unit: kg·m-1·s-1) at 20:00 on 29 July 2007 for typical case of cold vortex pattern (c), and 08:00 on 4 August 1996 for the case of typhoon low pressure pattern (d) (The black solid line area is Shanxi Province)

Fig.8 The box plot of average specific humidity at the rain beginning and the maximum average specific humidity during the process over the rainstorm area on 850， 700 hPa （a， Unit： g·kg-1） and the corresponding average abnormal degree （b） of 17 extreme rainstorm processes in Shanxi Province from June to September during 1981-2018

Fig.9 The water vapor flux divergence （black solid lines， Unit： 10-7 g·cm-2·s-1·hPa-1） on 700， 850 hPa and its negative abnormal degree （color shaded） of extreme rainstorm typical case of 700 hPa low vortex pattern （a， b）， interaction pattern between westerly low trough （vortex） and typhoon （c， d）， cold vortex pattern （e， f）， and typhoon low pressure pattern （g， h） extreme rainstorm （The red box is rainstorm area）

Tab.2 The statistics of the maximum value of water vapor flux convergence center during the process and its abnormal degree over the rainstorm area on 700， 850 hPa in Shanxi extreme rainstorm under different circulation classifications

统计量	700 hPa		850 hPa
统计量	水汽通量辐合中心过程最大值/（10^-7g·cm^-2·s^-1·hPa^-1）	异常度	水汽通量辐合中心过程最大值/（10^-7g·cm^-2·s^-1·hPa^-1）	异常度
700 hPa低涡型均值	-18	-8	-29	-6
西风带低槽（涡）与台风相互作用型均值	-12	-6	-18	-4
冷涡型均值	-19	-9	-33	-7
台风低压型	-24	-11	-55	-12

Fig.10 Conceptual model of extreme rainstorm typical case of 700 hPa low vortex pattern (a), interaction pattern between westerly low trough (vortex) and typhoon (b)

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