西南涡影响下重庆江北机场一次暴雨天气过程诊断分析及模式偏差分析

Diagnostic Analysis and Model Bias Assessment of a Heavy Rainfall Event at Chongqing Jiangbei Airport under the Influence of a Southwest Vortex

摘要: 利用ERA5再分析资料、模式探空资料对重庆江北机场2024年6月21日发生的一次大暴雨过程进行了诊断分析。结果表明：本次强降水过程环流背景复杂，500 hPa副高稳定与高原槽东移、700 hPa西南涡与850 hPa低涡叠加、地面锋面东移南下的多系统协同作用下，为水汽输送、动力抬升及不稳定能量积累提供较好条件。垂直速度场显示850~500 hPa整层强上升运动配合“高空辐散–低空辐合”机制，叠加低空高湿环境与CAPE激增、K指数升高，驱动此次强降水持续发展，该形势背景可作为典型的夏季西南涡暴雨理论模型。数值模式性能显示，SWC1KM、SWC3KM在落区位置和起始时间上表现一般，CMA-MESO综合表现较好。而睿图系统对降水开始时间及落区分布预报较准确，但降水量及落区精准度差异显著，其中SWC3KM最优、CMA-MESO次之、EC较差。

Abstract: Using ERA5 reanalysis data and model sounding data, a diagnostic analysis was conducted on a heavy rainfall event that occurred at Chongqing Jiangbei Airport on June 21, 2024. The results show that the background circulation of this intense precipitation event was complex: the 500 hPa subtropical high remained stable while the Tibetan Plateau trough shifted eastward, the 700 hPa southwest vortex and the 850 hPa low vortex overlapped, and the surface front moved eastward and southward. The synergistic effect of these multiple systems provided favorable conditions for moisture transport, dynamic lifting, and the accumulation of instability energy. The vertical velocity field indicated a strong upward motion through the 850~500 hPa layer combined with the “upper-level divergence-lower-level convergence” mechanism. Coupled with a low-level moist environment, a rapid increase in CAPE, and a rising K index, these factors drove the sustained development of heavy rainfall. This situation can serve as a typical theoretical model for summer Southwest Vortex heavy rainfall. The numerical model performance shows that SWC1KM and SWC3KM performed moderately in predicting the location and onset time of the rainfall area, while CMA-MESO performed relatively well overall. The Reitu System accurately predicted the start time and spatial distribution of precipitation, but there were significant differences in predicting rainfall intensity and the precision of affected areas, with SWC3KM performing the best, CMA-MESO second, and EC performing poorly.