Different driving mechanisms during two consecutive flash heavy rainfalls over the Sichuan Basin in China: A case study

IF 4.5 2区地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES

Atmospheric Research Pub Date : 2026-04-15 Epub Date: 2026-01-17 DOI:10.1016/j.atmosres.2026.108787

Changqing Liu , Jie Cao , Chengzhi Deng , Furong Qian

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Abstract

Two flash heavy rainfalls (FHRs) with short and extremely persistent durations during July 4–6, 2017 consecutively attacked the Sichuan Basin in China with breaking historical precipitation records. Based on multi-source precipitation datasets including rain gauge stations, satellite-based products, and reanalysis datasets, the two FHRs are thoroughly investigated in this study. High resolution numerical simulations are performed to analyze and compare the key mechanisms and diurnal characteristics between the two FHRs, together with other analytical techniques such as Barnes filtering and ageostrophic wind diagnostic equation. It is found that the precipitating event was dominated by combined effects of a low-level jet (LLJ) and the southwest vortex. Similarities and differences between the two FHRs are analyzed and concluded from the perspective of their key driving mechanisms. During the first FHR with short durations, geostrophic winds progressively intensified, while low-level southeasterlies underwent topographic convergence and uplifted over the northwestern basin. Under the background of weak geostrophic wind variations, the ageostrophic wind vector in the second FHR with extremely persistent durations exhibited pronounced clockwise diurnal rotation. Enhanced nocturnal southerlies poured moisture convergence into the basin, driving nighttime precipitation intensification. Steep basin-edge topography strengthened boundary layer friction (BLF) and intensified easterly ageostrophic winds. This deflection steered the LLJ southeastward, effectively channeling moisture into the storm area. Post-dawn enhancement of boundary layer friction increased ageostrophic moisture flux, slowing the precipitation decay rate. The inertial oscillation of ageostrophic winds critically governed the nocturnal enhancement and daytime suppression of rainfall by modulating moisture transport phases. Additionally, the post-dawn increase in boundary layer friction altered spatiotemporal configurations between ageostrophic winds and the LLJ, forming a key factor in precipitation process asymmetry.

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四川盆地两次连续暴雨的不同驱动机制

2017年7月4日至6日，中国四川盆地连续遭遇两次短时间极持续强降雨（FHRs），并打破历史降水记录。基于雨量站、卫星产品和再分析数据等多源降水数据集，对两种fhr进行了深入研究。通过高分辨率数值模拟，结合Barnes滤波和地转风诊断方程等分析技术，分析和比较了两种fhr的主要机制和日特征。结果表明，此次降水事件主要受低空急流（LLJ）和西南涡旋的共同作用。本文从二者的关键驱动机制出发，对二者的异同进行了分析和总结。在持续时间较短的第一次FHR期间，地转风逐渐增强，低层东南风在盆地西北部进行地形辐合并抬升。在弱地转风变化的背景下，极持续时间的第2次FHR地转风矢量表现出明显的顺时针日旋转。夜间增强的南风使水汽辐合进入盆地，推动夜间降水增强。陡峭的盆地边缘地形加强了边界层摩擦，增强了偏东地转风。这种偏转使LLJ向东南方向移动，有效地将湿气输送到风暴区。黎明后边界层摩擦的增强增加了地转湿通量，减缓了降水衰减速率。地转风的惯性振荡通过调节水汽输送阶段对夜间降雨的增强和白天降雨的抑制起关键作用。此外，黎明后边界层摩擦的增加改变了地转风与LLJ之间的时空配置，形成了降水过程不对称的关键因素。

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来源期刊

Atmospheric Research 地学-气象与大气科学

CiteScore

9.40

自引率

10.90%

发文量

460

审稿时长

47 days

期刊介绍： The journal publishes scientific papers (research papers, review articles, letters and notes) dealing with the part of the atmosphere where meteorological events occur. Attention is given to all processes extending from the earth surface to the tropopause, but special emphasis continues to be devoted to the physics of clouds, mesoscale meteorology and air pollution, i.e. atmospheric aerosols; microphysical processes; cloud dynamics and thermodynamics; numerical simulation, climatology, climate change and weather modification.