Abnormal characteristics of an extreme rainstorm process in autumn in Shanxi Province

doi:10.11755/j.issn.1006-7639(2021)-06-0984

Abstract

Abstract:

Based on daily precipitation data from 1960 to 2019 and hourly precipitation data in September 2019 from 109 meteorological stations in Shanxi Province and reanalysis data from European Centre of Medium-Range Weather Forecasts, the anomaly characteristics of the extremely regional rainstorm in central and southern Shanxi from 10 to 11 September 2019 and its causes were analyzed. The results are as follows: (1) The precipitation process affected a large area and lasted a long time, extreme daily precipitation events occurred at 46 stations, the daily precipitation of 11 stations exceeded the historical extreme value in September. (2) The water vapor, thermal and dynamic conditions in the middle and lower troposphere were better than the average state of regional rainstorm processes in the middle and south region of Shanxi since 1980, absolute values of normalized anomaly (|N|) of different physical quantities were higher than 2.5 and the upper quartile of historical data, especially for the water vapor and thermal conditions anomaly. (3) The subtropical high was anomalously strong and moved northward and westward, which led to abnormally strong water vapor and energy transport in mid-low troposphere, water vapor input in the western and southern boundaries of central and southern Shanxi Province played an important role in occurrence and development of extreme precipitation. (4) There was the potential instability in the inclined warm-moist southwesterly, warm shear line on 700 hPa and surface cold front initiated the convection, “train effect” produced due to echo moving continuously through heavy rain area. The stabilized shear line and abnormally cold wedge in lower troposphere provided sustained dynamic condition, abnormally plentiful vapor and its convergence maintained sustainably, which was the main causes of the extreme regional rainstorm, and the large range of physical quantities anomaly was the main influence factor of it.

Key words: regional rainstorm, normalized anomaly, abnormal characteristics

摘要：

利用山西省109个国家站1960—2019年逐日降水量、2019年9月逐时降水量以及1980—2019年欧洲中期天气预报中心1°×1°逐6 h再分析(ERA5)资料,对2019年9月10—11日山西中南部区域性极端暴雨过程的异常特征及其成因进行分析。结果表明:(1)此次降水过程影响范围大、持续时间长,46站发生极端日降水事件,其中11站日降水量突破9月历史极值。(2)对流层中低层水汽、热力、动力条件均优于1980年以来山西中南部区域性暴雨过程的平均态,不同物理量的标准化距平绝对值(|N|)均达到2.5以上,超过历史相关统计值的上四分位值,尤其是水汽和热力条件表现出一定的极端性。(3)副高位置异常偏西、偏北且强度异常偏强导致中低层水汽和能量输送异常充足,山西中南部地区西边界和南边界的水汽输入对极端降水的发生发展起到重要作用。(4)倾斜上升的西南暖湿气流中存在位势不稳定层,700 hPa暖式切变线和地面冷锋触发对流,回波持续通过暴雨区产生“列车效应”;稳定的切变线与异常的低层冷垫提供持续的动力条件,长时间维持异常充沛的水汽和水汽辐合是区域性极端暴雨的主要成因;大范围物理量场异常是导致此次极端降水事件发生的主要因素。

关键词: 区域性暴雨, 标准化距平, 异常特征

CLC Number:

P426.6

MIAO Qing, BAI Zibin, WANG Hongxia, GONG Yuanfa, DONG Chunqing. Abnormal characteristics of an extreme rainstorm process in autumn in Shanxi Province[J]. Journal of Arid Meteorology, 2021, 39(06): 984-994.

苗青, 白自斌, 王洪霞, 巩远发, 董春卿. 山西秋季一次极端暴雨过程的异常特征分析[J]. 干旱气象, 2021, 39(06): 984-994.

Figures/Tables 11

Fig.1 The distribution of precipitation (Unit: mm) in Shanxi Province and stations with extreme rainfall in central and southern Shanxi Province from 20:00 BST 10 to 20:00 BST 11 September 2019 (The red, black and gray dots are stations occurring extreme daily rainfall event, the black dots for rainfall more than historical record, gray dots for rainfall being second only to historical record, the red border for the schematic diagram of water vapor transport boundary in central and southern Shanxi Province)

Fig.2 The number of stations with heavy rain, rainstorm and both above during the regional heavy rain processes in central and southern Shanxi Province in September from 1960 to 2019

Fig.3 The combined reflectivity factor of 5 Doppler radar stations in Shanxi Province at 00:00 BST (a) and 13:38 BST (b) 11 September 2019 (Unit: dBZ)

Fig.4 The geopotential height field (the black lines, Unit: dagpm), θse(the shadow, Unit: K) on 500 hPa at 20:00 BST 10 September (a), sea level pressure field (the black lines, Unit: hPa), 2 m temperature anomaly field (the shadow, Unit: ℃) at 08:00 BST 11 September (b), wind field (the arrow vectors, Unit: m·s-1) and θse (the shadow, Unit: K) on 700 hPa (c) and 850 hPa (d) at 08:00 BST 11 September 2019

Fig.5 The meridional sections of θse (the isolines, Unit: K), vertical velocity (the shadow, Unit: Pa·s-1) and wind field (the arrow vectors, Unit: m·s-1) along 112°E at 20:00 BST 10 September (a), 02:00 BST (b) and 08:00 BST (c) 11 September 2019 (the black shadows for terrain height)

Fig.6 Box plots of absolute value of normalized anomaly (|N|) of different physical quantities during 20190911 process, 20050920 process and the historical regional rainstorm processes in the same region

Tab.1 Comparison of the different physical quantities during 20190911 process and the historical regional rainstorm processes in the same region

	θ_se/℃		Tadv/(10^-5 ℃·s^-1)		q/(g·kg^-1)		IFVQ/(10^-5 g·hPa^-1·cm^-2·s^-1)		Div₇/ (10^-5 s^-1)	P_WV/ mm
	θ_se7	θ_se5	Tadv₇	Tadv₅	q₇	q₅	IFVQ₇	IFVQ₅	Div₇/ (10^-5 s^-1)	P_WV/ mm
平均值	60.66	64.13	75.90	6.69	7.94	3.86	-1.01	-0.48	-1.39	37.02
最大值	73.47	75.68	116.8	12.45	10.65	5.72	-0.32	-0.15	-0.28	47.92
上四分位	65.14	69.42	83.50	7.54	9.20	4.89	-0.38	-0.10	-0.91	41.83
中位数	60.23	63.71	73.40	6.22	7.30	3.76	-0.79	-0.44	-1.06	34.28
下四分位	53.92	60.04	66.00	4.82	6.71	3.08	-1.77	-1.04	-2.02	31.23
最小值	51.98	54.39	58.10	2.42	5.64	2.02	-2.10	-1.33	-3.05	28.41
20190911过程	65.27	72.15	98.10	11.14	9.71	5.17	-2.10	-1.01	-2.29	42.35

Fig.7 The upper trough (the color lines) and 588 dagpm line (the color dashed lines) on 500 hPa from 20:00 BST 9 to 20:00 BST 12 September, normalized anomaly field of average geopotential height on 500 hPa from 20:00 BST 10 to 20:00 BST 11 September 2019 (the shadow)

Fig.8 Wind field (the arrow vectors, Unit: m·s-1) and normalized anomaly field of θse (the shadow) on 700 hPa (a) and 850 hPa (b) at 08:00 BST 11 September 2019

Fig.9 The moisture flux (the arrow vectors, only plotting the value greater than 4 g·hPa-1·cm-1·s-1), divergence of moisture flux (the red isolines, only plotting negative values, Unit: 10-5 g·hPa-1·cm-2·s-1) and normalized anomaly field of divergence of moisture flux (the shadow) on 500 hPa (a), 700 hPa (b) and 850 hPa (c) at 02:00 BST 11 September 2019

Fig.10 The 6-hour water vapor transport flux of the south-central border of Shanxi Province in the upper (a), middle (b), lower (c) and the whole (d) troposphere from 08:00 BST 10 to 20:00 BST 11 September 2019

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