Circulation characteristics and causal analysis of extreme summer precipitation over the Qinling Mountains and surrounding regions

doi:10.11755/j.issn.1006-7639-2026-03-0437

Abstract

Abstract:

To further understand the circulation characteristics and formation mechanisms of summer extreme precipitation over the Qinling Mountains and surrounding areas, this study used precipitation data from automatic weather stations and ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts from 2008 to 2025. Using spectral clustering method, the regional hourly extreme precipitation (RHEP) in the north and south of the Qinling Mountains (divided along 34°N) was classified into three and four typical circulation patterns, respectively. The dominant circulation features, water vapor, thermal, and dynamic conditions of summer RHEP were further investigated. The results are as follows: (1) At 200 hPa, all circulation types are influenced by divergence near the periphery of the South Asian High; at 500 hPa and below, these patterns are predominantly characterized by the combined effects of warm, moist air transport associated with the Western Pacific Subtropical High and short-wave troughs, shear lines, and similar features. Abundant moisture is transported by the peripheral airflow of the Subtropical High toward the Qinling Mountains and surrounding regions, producing pronounced convergence over regions of extreme precipitation. The combined effects of different circulation configurations and their interactions with complex terrain through orographic lifting and convergence intensify vertical motion, which is a key factor contributing to the spatial variability of RHEP occurrence. (2) In the lower troposphere, the periphery of the Subtropical High in each circulation pattern is characterized by anomalous southwesterly, southerly, or southeasterly airflow, with some types accompanied by anomalous northerly airflow on the northeastern side of the Qinghai-Xizang Plateau, favoring the confluence of cold and warm air and thereby promoting the occurrence of RHEP. (3) Water vapor diagnostic analysis reveals that multi-source water vapor from the Arabian Sea, Bay of Bengal, South China Sea, Western Pacific Ocean, and East China Sea converges over South China and East China, and is subsequently transported to the Qinling Mountains and its adjacent areas. In the areas north and south of the Qinling Mountains, most circulation patterns are predominantly influenced by water vapor input from the southern boundary of the lower-to-middle troposphere, while certain circulation types are predominantly influenced by water vapor input from the eastern boundary. (4) The peak frequency of RHEP for each circulation type occurs near specific topographic features, generally characterized by low convective inhibition (CIN) and high K-index values, indicating pronounced atmospheric instability, where even weak lifting mechanisms are sufficient to trigger the development of convection.

Key words: the Qinling Mountains and surrounding regions, extreme precipitation, circulation characteristics, special topography

摘要：

为深入认识秦岭及周边地区夏季极端降水的环流特征和形成机制，本文基于2008—2025年地面气象站降水数据和欧洲中期天气预报中心ERA5再分析资料，应用谱聚类方法，将秦岭北部和南部（以34°N为界划分）的区域小时极端降水（Regional Hourly Extreme Precipitation，RHEP）分别归纳为3类和4类典型环流型，探讨夏季RHEP的主要环流特征及水汽、热力和动力条件。结果表明：1）各类环流型200 hPa均受南亚高压边缘附近辐散场影响，500 hPa及以下多表现为西太平洋副高控制下的暖湿气流输送与短波槽、切变线等共同作用；副高外围气流向秦岭及周边输送充沛水汽，并在极端降水区形成明显辐合；不同环流配置及其与复杂地形的抬升辐合效应共同强化垂直运动，是导致RHEP高发区空间分布不同的重要原因。2）各类环流型对流层低层副高外围表现为西南、偏南或东南风异常，部分类型伴随青藏高原东北侧偏北风异常，有利于冷暖气流交汇，从而促进RHEP发生。3）水汽诊断分析表明，阿拉伯海、孟加拉湾、南海、西太平洋以及东海等多源水汽在华南及华东汇合后向秦岭及周边地区输送；秦岭北部和南部区域各环流型以对流层中低层南边界水汽输入为主，部分类型还受东边界水汽输入影响。4）各类环流型RHEP频次最大值均位于特殊地形附近，普遍具有较低对流抑制能量（Convective Inhibition，CIN）和较大的K指数，表明大气不稳定明显，较弱的抬升机制即可触发对流发展。

关键词: 秦岭及周边地区, 极端降水, 环流特征, 特殊地形

CLC Number:

P468

JING Yu, CHEN Chuang, ZHAO Qiang, LI Ming, HE Juan. Circulation characteristics and causal analysis of extreme summer precipitation over the Qinling Mountains and surrounding regions[J]. Journal of Arid Meteorology, 2026, 44(3): 437-450.

井宇, 陈闯, 赵强, 李明, 何娟. 秦岭及周边地区夏季极端降水环流特征及成因分析[J]. 干旱气象, 2026, 44(3): 437-450.

Figures/Tables 13

Fig.1 Topographical height of the Qinling Mountains and surrounding regions（Unit： m）

Fig. 2 The analysis of CH scores of different cluster numbers of wind fields (a, b) and temperature fields (c, d) in the study areas north (a, c) and south (b, d) of the Qinling Mountains based on the Spectral Clustering algorithm

Fig.3 Frequency of different RHEP circulation patterns in the study areas north and south of the Qinling Mountains during June-August， 2008-2025

Fig.4 Synoptic patterns of three RHEP circulation types in the study area north of the Qinling Mountains： 200 hPa geopotential height field （contours， Unit： dagpm）， divergence field （the color shaded， Unit： 10-6 s-1） and wind field （vectors， Unit： m·s-1）（a、b、c）； 500 hPa geopotential height field （black contours， Unit： dagpm）， temperature field （red isolines， Unit： ℃）， and wind field （vectors， Unit： m·s-1）， along with spatial distribution of the RHEP occurrence frequency （colour dots， Unit： times）（d、e、f）； 700 hPa geopotential height field （contours， Unit： dagpm）， vertically integrated water vapor flux divergence from the near-surface to 500 hPa （the color shaded， Unit： 10-5 kg·m-2·s-1）， and wind field （vectors， Unit： m·s-1）（g、h、i）； 850 hPa geopotential height field （contours， Unit： dagpm）， vertically integrated water vapor flux from the near-surface to 500 hPa （the color shaded， Unit： kg·m-1·s-1）， and wind field （vectors， Unit： m·s-1）（j、k、l）（★ denotes the location with the highest frequency of RHEP occurrence， the gray shaded denotes topography， the black frame denotes the boundary of the study area north of the Qinling Mountains）

Fig.5 Synoptic patterns of four RHEP circulation types in the study area south of the Qinling Mountains： 200 hPa geopotential height field （contours， Unit： dagpm）， divergence field （the color shaded， Unit： 10-6 s-1） and wind field （vectors， Unit： m·s-1）（a、b、c、d）； 500 hPa geopotential height field （black contours， Unit： dagpm）， temperature field （red isolines， Unit： ℃）， and wind field （vectors， Unit： m·s-1）， along with spatial distribution of the RHEP frequency （colour dots， Unit： times）（e、f、g、h）； 700 hPa geopotential height field （contours， Unit： dagpm）， vertically integrated water vapor flux divergence from the near-surface to 500 hPa （the color shaded， Unit： 10-5 kg·m-2·s-1）， and wind field （vectors， Unit： m·s-1）（i、j、k、l）； 850 hPa geopotential height field （contours， Unit： dagpm）， vertically integrated water vapor flux from the near-surface to 500 hPa （the color shaded， Unit： kg·m-1·s-1）， and wind field （vectors， Unit： m·s-1）（m、n、o、p）（★ denotes the location with the highest frequency of RHEP occurrence， the gray shaded denotes topography， the black frame denotes the boundary of the study area south of the Qinling Mountains）

Fig.6 The 700 hPa geopotential height （contours， Unit： dagpm）， geopotential height anomalies （the color shaded， Unit： dagpm）， and wind field anomalies （vectors， Unit： m·s-1） of the N1 （a） and N3 （b） RHEP circulation patterns in the study area north of the Qinling Mountains as well as the S1 （c） and S4 （d） RHEP circulation patterns in the study area south of the Qinling Mountains （The dotted areas passed the significance test at the 95% confidence level， the black and red frames denote the boundaries of the study areas north and south of the Qinling Mountains， respectively）

Fig.7 Vertically integrated mean water vapor flux from near the surface to 300 hPa （vectors， Unit： kg·m-1·s-1） of the N1 （a） and N3 （b） RHEP circulation patterns in the study area north of the Qinling Mountains as well as the S1 （c） and S4 （d） RHEP circulation patterns in the study area south of the Qinling Mountains （The black and red frames denote the boundaries of the study areas north and south of the Qinling Mountains， respectively）

Tab.1 Water vapor budgets of different RHEP circulation patterns at the boundaries of the study areas north and south of the Qinling Mountains

环流型	东边界			南边界			西边界			北边界
环流型	低层	中层	高层	低层	中层	高层	低层	中层	高层	低层	中层	高层
N1	1.52	20.72	11.83	-50.28	-24.05	-3.96	-1.27	-8.54	-8.74	1.35	-2.52	4.72
N2	15.10	28.65	13.27	-79.15	-34.14	-0.80	-0.84	-5.10	-12.62	-6.89	-4.60	2.20
N3	-73.05	-15.97	1.54	-35.22	-16.29	-2.68	4.70	3.97	-0.24	52.07	13.24	0.97
S1	46.35	25.62	6.09	-111.89	-39.13	0.07	0	0.97	-4.21	-8.33	-5.07	-0.16
S2	24.59	27.71	11.23	-93.72	-38.77	-0.74	0	-0.04	-7.86	-11.16	-10.34	1.25
S3	10.17	18.98	5.73	-120.75	-46.59	0.34	0	-2.39	-4.11	26.23	13.43	0.06
S4	8.60	1.40	-0.59	-146.4	-59.12	-2.55	0	-1.64	-4.99	64.02	49.86	13.26

Fig.8 Longitude-height cross-sections （a， b， c） of the wind field （vectors， Unit： m·s-1）， temperature advection （the color shaded， Unit： 10-5 ℃·s-1）， and vertical velocity （green dashed lines， Unit： Pa·s-1）， and latitude-height cross-sections （d， e， f） of the synthesis of meridional wind-vertical velocity （the vertical velocity is magnified by 100 times， vectors， Unit： m·s-1）， divergence （the color shaded， Unit： 10-5 s-1）， and relative humidity （green isolines， Unit： %） along the location of the maximum RHEP occurrence frequency of the three RHEP circulation types over the study area north of the Qinling Mountains （★ indicates the location of the maximum RHEP occurrence frequency for each circulation pattern， the gray shaded represents terrain）

Fig. 9 The variation of terrain-forced vertical velocity along longitude (a) and latitude (b) at the locations with maximum RHEP occurrence frequency of the three RHEP circulation patterns over the study area north of the Qinling Mountains

Fig.10 Longitude-height cross-sections （a， b， c， d） of the wind field （vectors， Unit： m·s-1）， temperature advection （the color shaded， Unit： 10-5 ℃·s-1）， and vertical velocity （green dashed lines， Unit： Pa·s-1）， and latitude-height cross-sections （e， f， g， h） of the synthesis of meridional wind-vertical velocity （the vertical velocity is magnified by 100 times， vectors， Unit： m·s-1）， divergence （the color shaded， Unit： 10-5 s-1）， and relative humidity （green isolines， Unit： %） along the location of the maximum RHEP occurrence frequency of the four RHEP circulation types over the study area south of the Qinling Mountains （★ indicates the location of the maximum RHEP occurrence frequency for each circulation pattern， the gray shaded represents terrain）

Fig. 11 The variation of terrain-forced vertical velocity along longitude (a) and latitude (b) at the locations with maximum RHEP occurrence frequency of the four RHEP circulation patterns over the study area south of the Qinling Mountains

Fig.12 Composite T-ln P diagram of RHEP circulation patterns N1 （a） and N3 （b） over the study area north of the Qinling Mountains， as well as S2 （c） and S4 （d） over the study area south of the Qinling Mountains （The red curve is environmental temperature， the green curve is environmental dew point temperature， the black curve is parcel temperature， the black dot is lifting condensation level）

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