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<p>This study compares five quasi-stationary Southwest Vortex (SWV) events that induced heavy rainfall, using the CRA40 reanalysis data from the China Meteorological Administration. Results indicate that the Tibetan Plateau’s topography and the strong westward-extending Western Pacific subtropical high (WPSH) act as critical blocking factors, stabilizing the SWV in the Sichuan-Chongqing region. Depending on the WPSH configuration, two types of quasi-stationary SWV processes are identified: north–south and east–west distributions. Long stagnation of the SWV is linked to regional heavy precipitation. North–south SWV processes generally exhibit a larger rainfall range and stronger intensity than east–west processes. They feature significantly higher total column water vapor content and stronger, wider southwesterly airflow. The strongest water vapor transport band around 800 hPa is the main moisture source. Both types occur within a favorable synoptic environment of cyclonic vorticity, low-level convergence, and ascending motion, where vertical velocity plays an important role in modulating precipitation intensity. The combined forcing of the Tibetan Plateau and the WPSH, along with direct impacts from moisture flux convergence and vertical motion, governs the anomalous evolution of quasi-stationary SWVs and their resultant precipitation.</p>

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Characteristics of quasi-stationary Southwest Vortex and its mechanisms affecting precipitation

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月29日

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  • Gong Chen,
  • Ping Lu

摘要

This study compares five quasi-stationary Southwest Vortex (SWV) events that induced heavy rainfall, using the CRA40 reanalysis data from the China Meteorological Administration. Results indicate that the Tibetan Plateau’s topography and the strong westward-extending Western Pacific subtropical high (WPSH) act as critical blocking factors, stabilizing the SWV in the Sichuan-Chongqing region. Depending on the WPSH configuration, two types of quasi-stationary SWV processes are identified: north–south and east–west distributions. Long stagnation of the SWV is linked to regional heavy precipitation. North–south SWV processes generally exhibit a larger rainfall range and stronger intensity than east–west processes. They feature significantly higher total column water vapor content and stronger, wider southwesterly airflow. The strongest water vapor transport band around 800 hPa is the main moisture source. Both types occur within a favorable synoptic environment of cyclonic vorticity, low-level convergence, and ascending motion, where vertical velocity plays an important role in modulating precipitation intensity. The combined forcing of the Tibetan Plateau and the WPSH, along with direct impacts from moisture flux convergence and vertical motion, governs the anomalous evolution of quasi-stationary SWVs and their resultant precipitation.