Local circulation study of a sudden rainfall process in mountainous area of Mianyang, Sichuan Province

doi:10.11755/j.issn.1006-7639-2025-02-0254

Abstract

Abstract:

Studying the basic characteristics of sudden rainfall events in mountainous areas, along with the local circulations induced by dynamic and thermodynamic processes, is of great significance for improving the accuracy and timeliness of forecasting sudden heavy rainstorms in such environments. This paper investigates two sudden rainfall events in the mountainous region of Mianyang, China, based on the china multi-source merged precipitation analysis system (CMPAS), black body temperature (TBB) data from the FY-2G satellite, and ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Diagnostic analyses and numerical simulations were conducted using equations representing flow around, up, and over mountains.The results indicate that both sudden torrential rainfall events in mountainous areas occurred under the influence of the western Pacific subtropical high within a weak synoptic-scale environment. The convergence of cold and warm air masses, combined with favorable moisture supply and high-temperature conditions, served as the primary triggers for the rainstorms. Cross-mountain airflow induced by terrain obstruction generated both around and over flow motions. Within the rainfall zone, these processes enhanced vertical ascent and localized vortices. When weak cold air intruded, flow over dominated, and the combined effects of ascending and deflected flows created favorable dynamic conditions for the initiation and intensification of the sudden rainstorms. In contrast, under strong cold air influence, the contributions of around and over flows to heavy rainfall were significantly reduced. The around and over flows within the rainstorm area were coupled with the intensity of precipitation. During the rainfall process, the cessation of surface heat input led to a significant weakening of thermal disturbances near the rainfall area, preventing the formation of local circulation in the western basin, resulting in weakened around and over flows, and the disappearance of the convergence zone, which led to a noticeable reduction in simulated precipitation and the disappearance of the heavy precipitation center. Numerical simulations for both events demonstrated that latent heat played a more critical role than sensible heat in driving precipitation.

Key words: sudden rainfall in mountainous, flow around and flow over, local circulation, WRF simulation, sensible heat and latent heat

摘要：

研究山地突发性降雨过程的基本特征及其动力、热力引起的局地环流，对提高山地环境下突发性暴雨的预报准确性和及时性具有重要意义。本文选取绵阳地区两次山地突发性降雨事件，基于中国逐日降水快速融合实况分析产品（CMA Multi-source merged Precipitation Analysis System，CMPAS）、FY-2G卫星相当黑体亮温（Black Body Temperature，TBB）及欧洲中期天气预报中心（European Centre for Medium-Range Weather Forecasting，ECMWF）ERA5再分析资料，采用绕流、爬流和过山气流方程进行诊断分析和数值模拟试验。结果表明，两次突发性降雨均发生在西太平洋副热带高压控制的弱天气系统背景下，适宜的水汽条件、高温环境及冷暖空气交汇是暴雨触发的主要因素。山地阻挡作用促使过山气流产生绕流和爬流运动，在暴雨区形成上升运动和局地涡旋。在弱冷空气影响下，爬流运动占主导，爬流与绕流共同促进突发性暴雨的发生与发展；而在强冷空气影响下，二者对暴雨的促进作用减弱。暴雨区内绕流和爬流与降水强度耦合。降雨过程中，地面热源输入的消失导致降雨区附近地表热力扰动明显减弱，使盆地西部难以形成局地环流，进而削弱绕流和爬流，同时辐合区消失，导致数值模拟区域降水量明显减少，强降水中心消失。两次降雨过程中数值模拟试验结果均表明，相较于感热，潜热对降水起主要作用。

关键词: 山地突发性降雨, 绕流和爬流, 局地环流, WRF模拟, 感热和潜热

CLC Number:

P426.62

SUN Zichuan, ZHANG Qingyan, CHEN Ying, YUAN Benhe, WAN Cong, OUYANG Xin. Local circulation study of a sudden rainfall process in mountainous area of Mianyang, Sichuan Province[J]. Journal of Arid Meteorology, 2025, 43(2): 254-264.

孙自川, 张青艳, 陈颖, 袁本荷, 万丛, 欧阳欣. 四川绵阳山地突发性降雨过程的局地环流研究[J]. 干旱气象, 2025, 43(2): 254-264.

Figures/Tables 11

Tab.1 The contents and intention of WRF numerical simulation test

名称	内容	意义
控制试验	采用Dudhia短波辐射方案、Noah陆面方案、NSSL 2-moment云微物理参数方案、Tiedtke积云参数化方案、Revised Monin-Obu khov近地层方案、RRTM长波辐射方案、YSU边界层方案（付智龙等，2022）	验证模型准确性
敏感性试验A	关闭模式中的感热和潜热（isfflx=0），其余设置与控制组一致	探究地面热源对局地环流的影响
敏感性试验B	关闭模式中的潜热（heating=1），其余设置与控制组一致	探究潜热在地面热源中的作用

Fig.1 Model domain superimposed terrain height

Fig.2 The distribution of 24-h accumulated precipitation at 20：00 on 11 （a） and at 20：00 on 15 （b） July 2022 in Mianyang （The red lines indicates the path along which the sensitivity experiment was conducted； the red curve rang indicates the Mianyang City， the same as below）

Fig.3 The 500 hPa geopotential height field (orange contours, Unit: dagpm) and wind field of 850 hPa (wind vectors, Unit: m·s-1) (a, b) and geopotential height field (blue contours, Unit: dagpm) and divergence field (the color shaded, Unit: 10-4 s-1) at 200 hPa (c, d) at 20:00 on 11 (a, c) and at 20:00 on 15 (b, d) July 2022

Fig.4 The TBB (the color shaded, Unit: ℃), wind field (wind vectors, Unit: m·s-1) and vertical velocity (blank lines, Unit: Pa·s-1) at 700 hPa at different times on 12 July and from 15 to 16 July, 2022

Tab.2 Atmospheric environmental field changes during two precipitation processes in July 2022

日期	时间	大气柱水汽总量/（kg·m^-2）	850 hPa		700 hPa
日期	时间	大气柱水汽总量/（kg·m^-2）	温度平流/ （K·s^-1）	假相当位温/K	垂直速度/（Pa·s^-1）
11日	14：00	43.78	1.10×10^-05	368.11	-0.39
11日	20：00	45.70	2.56×10^-05	368.75	-1.27
12日	02：00	44.93	-1.30×10^-06	365.95	-1.88
12日	07：00	43.50	-2.60×10^-06	365.62	-1.45
15日	14：00	32.65	7.57×10^-05	367.48	-0.29
15日	20：00	37.45	-1.80×10^-05	366.34	-0.47
16日	02：00	36.84	-1.90×10^-05	366.41	-0.87
16日	07：00	38.26	-1.80×10^-05	361.11	-0.23

Fig.5 The Fr （blank lines） and dimensionless mountain height （light gray lines） at 775~750 hPa and 750 hPa relative vorticity （the color shaded， Unit： 10-5 s-1） at 20：00 on 11 （a）， 02：00 on 12 （b）， 20：00 on 15 （c） and 02：00 on 16 （d） July 2022 （The dark dots indicate the locations of heavy rainfall centers）

Tab.3 The variations of the magnitude， meridional and zonal components of flow around and flow over at 750 hPa at the two precipitation processes in Mianyang City and the changes in precipitation

日期	时间	绕流/（m∙s^-1）			爬流/（m∙s^-1）			1 h降水量/mm
日期	时间	经向分量	纬向分量	模值	经向分量	纬向分量	模值	1 h降水量/mm
11日	17：00	0.06	0.03	0.07	1.20	2.26	2.56	0
11日	18：00	0.23	0.12	0.26	1.25	2.34	2.66	1.6
12日	03：00	0.18	0.09	0.20	1.40	2.63	2.98	3.3
12日	04：00	0.79	0.42	0.89	1.36	2.55	2.89	13.6
16日	00：00	0.22	-0.74	0.78	-0.15	0.05	0.16	0
	01：00	0.12	-0.42	0.43	-0.46	0.14	0.48	15.4
	04：00	0.27	-0.89	0.93	-0.30	0.09	0.31	8.8
	05：00	-0.19	0.63	0.66	-1.04	0.31	1.09	23.5

Fig.6 Distribution of the 24-h accumulated precipitation of control experiment (a, d), group A (b, e) and group B (c, f) of sensitivity experiment at 20:00 on 11 (a, b, c) and 20:00 on 15 (d, e, f) July 2022

Fig.7 Cross section profile of the perturbation virtual temperature (the color shaded, Unit: K) and perturbation zonal wind speed (black lines, Unit: m·s-1) simulated by WRF model along red line in fig.2 in July 2022 (Perturbation virtual temperature is deviation from the mean height within the profile, perturbation zonal wind speed is deviation from the daily mean zonal wind speed; the red arrows indicate the direction of the mountain-plain circulation, the grey area represents the terrain)

Fig.8 The 700 hPa divergence (color shaded, Unit: 5×10-3 s-1), the mode of flow around (red lines, Unit: m?s-1) and flow over (cyan lines, Unit: m?s-1) simulated by WRF model during the two precipitation events in July 2022

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