Classification and meteorological element evolution of rainstorm in the eastern Helan Mountain foothills

doi:10.11755/j.issn.1006-7639-2025-03-0413

Abstract

Abstract:

In order to strengthen the application of densified automatic station data in rainstorm forecast in the eastern Helan Mountain foothills, based on hourly surface meteorological observations and ERA5 reanalysis data, 17 rainstorm events in this area from 2016 to 2021 were classified into cold-warm air convergence type, warm-sector type, and weak cold air intrusion type, according to the intensity of cold air. The precipitation distribution, circulation characteristics, and the evolution of surface meteorological elements were then comparatively analyzed. The results show that cold-warm air convergence rainstorms are characterized by a deep upper-level trough and an extensive low-level high-humidity zone, but with relatively weak southerly winds and water vapor flux. These storms exhibit a wide precipitation area and high average rainfall, but the precipitation efficiency is lower than that of warm-sector rainstorms. Warm-sector rainstorms have the strongest low-level southerly winds and moisture flux, but the upper-level divergence is the weakest and the high-humidity zone is fragmented. These storms are marked by high precipitation efficiency, strong locality, and extreme intensity. In weak cold air intrusion rainstorms, the low-level warm and moist conditions are better than in the cold-warm air convergence type, and the precipitation and convective intensity which triggered by upper-level cold air are stronger than those of the cold-warm air convergence type. One hour before the onset of precipitation, all three types of rainstorms exhibit temperature drop, pressure rise, and increased wind speed, with temperature changes being the most significant, while dew point temperature varies between cases. In the five hours prior to precipitation, temperature decreased and relative humidity increased, with the most pronounced changes occurring one hour before rainfall onset. After precipitation began, these variables tended to stabilize. However, the timing and magnitude of temperature drops and the rate of relative humidity increase differed among the storm types. Dew point temperature first increased and then decreased, peaking from 1 hour before to 2 hours after rainfall onset. Wind speed variations also differed across storm types. The indicators developed in this study performed best for warm-sector type rainstorms, achieving a TS (threat score) of 48.65%, followed by the cold-warm air convergence type, with the weakest performance in the weak cold air intrusion type. The prediction accuracy of humidity, pressure, and dew point temperature indicators was relatively high (mostly exceeding 50.00%, some over 55.00%), indicating potential for enhancing rainstorm monitoring and early warning. In contrast, indicators based on temperature change (less than 50.00%) and wind speed variation (around 30.00%) showed weaker predictive capability, indicating the need for further optimization.

Key words: heavy rainstorm, the features of rainstorm, circulation traits, meteorological elements, preceding attributes

摘要： 为加强加密自动站资料在贺兰山东麓暴雨预报中的应用，对2016—2021年该地17次暴雨过程，基于逐时地面气象要素和ERA5再分析资料，按照冷空气强度将其分为冷暖交汇型、暖区型和弱冷空气入侵型，并对比分析其降水分布、环流特征及地面气象要素演变规律。结果表明，冷暖交汇型暴雨高空槽深厚，低层高湿区范围广，但偏南风和水汽通量均较弱，降水范围广，平均雨量大，但降水效率低于暖区型暴雨；暖区型暴雨低层水汽通量及偏南风最强，但高层辐散场最弱，高湿区分散，降水效率高，局地性、极端性强；弱冷空气入侵型暴雨低层暖湿条件优于冷暖交汇型，在高层冷空气触发下，降水量级和对流性强于冷暖交汇型。降水开始前1 h，3类暴雨均降温、升压、风速增大，其中气温变化最明显，露点温度变化各有差异。降水开始前5 h，气温下降、相对湿度上升，以降水前1 h变幅最大，降水开始后趋于稳定，但各型暴雨开始降温时次和幅度不同，相对湿度增长速度不同；露点温度先升后降，降水前1 h至降水后2 h出现极大值；风速变化各有不同。本文得出的指标对于暖区型暴雨效果相对最好，TS评分48.65%，冷暖交汇型次之，弱冷空气入侵型最差。变湿、变压以及露点温度变化3类指标达标率较高（多在50.00%以上），部分超过55.00%，可用于提高暴雨监测预警能力；变温（达标率不足50.00%）和变风（达标率约30.00%）指标预报能力较弱，仍需优化。

关键词: 暴雨, 降水特点, 环流特征, 气象要素, 前置特征

CLC Number:

P466

CHEN Min, CHEN Yuying, CHEN Rong, CHEN Yuxi, YANG Yuanyuan. Classification and meteorological element evolution of rainstorm in the eastern Helan Mountain foothills[J]. Journal of Arid Meteorology, 2025, 43(3): 413-423.

陈敏, 陈豫英, 陈荣, 陈宇曦, 杨苑媛. 贺兰山东麓暴雨天气分型及气象要素演变特征研究[J]. 干旱气象, 2025, 43(3): 413-423.

Figures/Tables 9

Tab.1 Classification and statistical characteristics of 17 rainstorm events in the eastern Helan Mountain foothills from 2016 to 2021

过程分类	平均持续时间/h	平均雨量/mm	暴雨平均站数/个	大暴雨平均站数/个	特大暴雨平均站数/个	短时强降水平均站数/个	最大累计雨量/mm	最大雨强/（mm·h^-1）
冷暖交汇型	15.3	19.0	26.4	0.7	0	28.9	119.1	58.0
暖区型	18.0	12.1	20.7	3.0	0.8	39.2	277.6	84.5
弱冷空气入侵型	14.0	12.9	23.0	1.3	0	36.5	136.2	54.5

Fig.1 Statistics of rainstorm frequency (Unit: times) for cold-warm air convergence type (a), warm-sector type (b), and weak cold air intrusion type (c)

Fig.2 Rainstorm centers (a) and station counts of short-time heavy rainstorm by time period (b) of three types of rainstorm in the eastern foothills of Helan Mountain from 2016 to 2021

Fig.3 The average geopotential height field (contours, Unit: dagpm) and jet flow area with wind speed greater than or equal to 30 m·s-1 (the color shaded) at 200 hPa (a, c, e) and the average geopotential height field (contours, Unit: dagpm) and wind field (wind vectors, Unit: m·s-1) at 500 hPa (b, d, f) of rainstorm for cold-warm convergence type (a, b), warm-sector type (c, d), and weak cold air intrusion type (e, f) (The red line range indicates Ningxia, the same as below)

Fig.4 The composite wind field (vector arrows, Unit: m·s-1), relative humidity field (the green shadow, Unit: %) and water vapor flux greater than 8×105 g·hPa·cm-1·s-1 (blue isolines, Unit: 105 g·hPa·cm-1·s-1) at 700 hPa (a, c, e) and 850 hPa (b, d, f) of rainstorm for cold-warm convergence type (a, b), warm-sector type (c, d), and weak cold air intrusion type (e, f)

Fig.5 Box plots of 1-hour temperature change (a), 1-hour dew point temperature variation (b), 3-hour pressure change (c) and 1-hour wind speed variation (d) at the onset of rainstorm for cold-warm air convergence type, warm-sector type, and weak cold air intrusion type

Fig.6 The variation of average wind speed, temperature (a, c, e), and relative humidity and dew point temperature (b, d, f) before and after the onset of rainstorm for different station types of cold-warm air convergence type (a, b), warm-sector type (c, d) and weak cold air intrusion type (e, f)

Tab. 2 Statistics of variation index with surface meteorological elements in different rainstorm types

暴雨类型	变温	变湿	变压	风速变化	露点温度变化
冷暖交汇型	前4 h降温6 ℃且前1 h降温2 ℃	前1 h增幅10% 且湿度≥90%	3 h变幅-4.0~-1.0 hPa		前1 h降温0.8~1.0 ℃
暖区型	前5 h降温2~4 ℃	前1 h增幅5%~8%且湿度≥90%	3 h变幅0.2~3.1 hPa	前3 h增大3~4 m·s^-1	前1 h降温0.8~1.0 ℃
弱冷空气侵入型	前2 h降温4~6 ℃	前1 h增幅12%且湿度≥90%	3 h变幅-2.5~3.2 hPa	前3 h增大2 m·s^-1	前1 h降温0.8~3.5 ℃

Tab. 3 Comparison of inspection results of surface meteorological element indexes in 17 rainstorm events 单位：%

暴雨类型	TS评分	空报率	漏报率	变温达标率	变湿达标率	变压达标率	变风达标率	露点温度变化达标率
暖区型	48.65	40.32	27.53	35.35	57.77	53.43	30.97	53.58
冷暖交汇型	45.98	43.77	28.39	49.65	56.36	63.21	32.54	55.24
弱冷空气侵入型	41.37	45.67	36.56	42.44	51.16	47.92	26.24	50.47

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