Liu et al. (2026) Different driving mechanisms during two consecutive flash heavy rainfalls over the Sichuan Basin in China: A case study

Identification

• Journal: Atmospheric Research
• Year: 2026
• Date: 2026-01-17
• Authors: C. Liu, Jie Cao, Chengzhi Deng, Feng Qian
• DOI: 10.1016/j.atmosres.2026.108787

Research Groups

• State Key Laboratory of Climate System Prediction and Risk Management/Key Laboratory of Meteorological Disaster, Ministry of Education/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/School of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China
• Chongqing Meteorological Observatory/Key Open Laboratory of Transforming Climate Resources to Economy, Chinese Meteorological Administration, Chongqing 401147, China

Short Summary

This study investigates the distinct driving mechanisms and diurnal characteristics of two consecutive flash heavy rainfalls (FHRs) that occurred over the Sichuan Basin in July 2017, revealing the critical role of ageostrophic winds and boundary layer friction in modulating their precipitation patterns.

Objective

• To thoroughly investigate and compare the key mechanisms and diurnal characteristics between two consecutive flash heavy rainfalls (FHRs) that attacked the Sichuan Basin.

Study Configuration

• Spatial Scale: Sichuan Basin, China
• Temporal Scale: July 4–6, 2017

Methodology and Data

• Models used: High resolution numerical simulations, Barnes filtering, ageostrophic wind diagnostic equation.
• Data sources: Multi-source precipitation datasets including rain gauge stations, satellite-based products, and reanalysis datasets.

Main Results

• The precipitating events were dominated by combined effects of a low-level jet (LLJ) and the southwest vortex.
• During the first FHR (short duration), geostrophic winds progressively intensified, leading to topographic convergence and uplift of low-level southeasterlies over the northwestern basin.
• In the second FHR (extremely persistent duration), under weak geostrophic wind variations, the ageostrophic wind vector exhibited pronounced clockwise diurnal rotation.
• Enhanced nocturnal southerlies, driven by ageostrophic winds, poured moisture convergence into the basin, intensifying nighttime precipitation.
• Steep basin-edge topography strengthened boundary layer friction (BLF), intensifying easterly ageostrophic winds, which steered the LLJ southeastward and channeled moisture into the storm area.
• Post-dawn enhancement of BLF 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.
• A post-dawn increase in BLF altered the spatiotemporal configurations between ageostrophic winds and the LLJ, forming a key factor in precipitation process asymmetry.

Contributions

• Provides a detailed comparative analysis of the distinct driving mechanisms for two consecutive flash heavy rainfall events in the Sichuan Basin.
• Highlights the critical role of ageostrophic winds and boundary layer friction in modulating the diurnal cycles and asymmetry of flash heavy rainfall, particularly for persistent events.
• Offers insights into the complex interactions between large-scale circulation, topography, and boundary layer processes in shaping extreme precipitation events.

Funding

Not specified in the provided text.

Citation

@article{Liu2026Different,
  author = {Liu, C. and Cao, Jie and Deng, Chengzhi and Qian, Feng},
  title = {Different driving mechanisms during two consecutive flash heavy rainfalls over the Sichuan Basin in China: A case study},
  journal = {Atmospheric Research},
  year = {2026},
  doi = {10.1016/j.atmosres.2026.108787},
  url = {https://doi.org/10.1016/j.atmosres.2026.108787}
}