This study investigates the formation of a type of mesoscale vortex around the Sichuan Basin (i.e., the southwest vortex [SWV]) that usually induces heavy precipitation, based on a semi‐idealized simulation of eight similar SWV‐formation events. After producing a reasonable SWV that shares salient features with the events used in composite, a trajectory analysis is conducted and an along‐track vorticity budget is constructed. The results show that approximately 64.7% of the air particles related to SWV formation originate from four source regions outside the vortex. The largest contribution of cyclonic vorticity associated with the SWV formation (approximately 67.7%) comes from the lower levels southwest of the vortex and is due mainly to tilting. The second‐largest contribution (approximately 19.4%) is made by air particles that originate from the upper levels south of the SWV and is also due mainly to tilting. By contrast, for the other two sources (the upper levels west and southwest of the vortex), the convergence‐related horizontal shrinking generally dominates their cyclonic‐vorticity production. Overall, along the tracks of the air particles, vertical motions and water‐vapor phase transitions affect the vorticity variation significantly via modulating divergence‐related vorticity production/dissipation (i.e., the stretching effect), and this is vital for the SWV formation.

中文翻译：

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四川盆地周围一种强降水产生的中尺度涡旋的形成：沿轨道涡度预算分析

这项研究基于对八个相似的SWV形成事件的半理想化模拟，研究了通常诱发大量降水的四川盆地周围一种中尺度涡旋的形成（即西南涡[SWV]）。在产生与合成中使用的事件具有显着特征的合理SWV之后，进行轨迹分析并构造沿轨道的涡度预算。结果表明，与SWV形成有关的空气颗粒中约有64.7％来自涡旋外部的四个源区。与SWV形成有关的气旋涡度的最大贡献（约67.7％）来自涡旋西南的较低水平，主要是由于倾斜。第二大捐款（约19。4％的空气颗粒是由SWV南部的高层空气中产生的，也主要是由于倾斜造成的。相比之下，对于其他两个源（涡旋西和西南的高层），与收敛有关的水平收缩通常主导着旋风涡的产生。总体而言，沿着空气粒子的轨迹，垂直运动和水汽相变通过调节与发散有关的涡度的产生/消散（即拉伸效应）而显着影响涡度变化，这对于SWV的形成至关重要。