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<p>Tibetan Plateau (TP)-originated mesoscale convective systems (TP_MCSs) played a crucial role in driving record-breaking rainfall during the abnormal 2020 Mei-Yu season (MY2020), though their anomalous background environment and quantitative precipitation contributions remained unclear. Using FY-2G TBB, GPM-IMERG precipitation, and ERA5 reanalysis data, we partially address this knowledge gap, revealing that: (i) TP_MCSs exhibited abnormal activity during MY2020, 15% of TP_MCSs vacated the TP, a proportion exceeding that in normal Mei-Yu years, especially for types with the longest moving distances (termed as Type III, ~ 3.4% in 2020 compared with that of &lt; 0.1% in normal years). (ii) The TP and middle-to-lower reaches of the Yangtze River experienced maximum TP_MCS-related precipitation contribution rates (~ 75%) and amounts (&gt; 505&#xa0;mm), respectively. However, mechanisms differed markedly between the TP (governed by TP_MCS frequency) and downstream regions (dominated by convective intensity). (iii) The anomalous background environment, characterized by an enhanced upper-level westerly jets, cyclonic circulations over TP/Sichuan Basin, and enhanced low-level southerly moisture flux, drove frequent vacating of TP_MCSs in MY2020. These TP_MCSs, in turn, amplified the anomalous precipitation by intensifying upward motion through the release of latent heat from condensation. (iv) The key factors controlling the moving distance of TP_MCSs (particularly Type III) varied with their developmental stages. The potential for eastward propagation was primarily determined by Tibetan low-pressure systems, which enhanced the westerly steering flows. In contrast, the migration into the Yangtze River was largely dictated by southwest vortices, which intensified southerly winds that, in turn, drove enhanced moisture transport and convergence. These findings advance dynamical understanding of TP_MCS roles in extreme Mei-Yu rainfall and provide a benchmark for Yangtze River precipitation forecasting.</p>

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On the mesoscale convective systems generated over the Tibetan Plateau during the 2020 abnormal Mei-Yu season: key features and contributions

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月1日

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  • Wen Zhou,
  • Shenming Fu,
  • Xiaofang Wang,
  • Chunguang Cui,
  • Yang Hu

摘要

Tibetan Plateau (TP)-originated mesoscale convective systems (TP_MCSs) played a crucial role in driving record-breaking rainfall during the abnormal 2020 Mei-Yu season (MY2020), though their anomalous background environment and quantitative precipitation contributions remained unclear. Using FY-2G TBB, GPM-IMERG precipitation, and ERA5 reanalysis data, we partially address this knowledge gap, revealing that: (i) TP_MCSs exhibited abnormal activity during MY2020, 15% of TP_MCSs vacated the TP, a proportion exceeding that in normal Mei-Yu years, especially for types with the longest moving distances (termed as Type III, ~ 3.4% in 2020 compared with that of < 0.1% in normal years). (ii) The TP and middle-to-lower reaches of the Yangtze River experienced maximum TP_MCS-related precipitation contribution rates (~ 75%) and amounts (> 505 mm), respectively. However, mechanisms differed markedly between the TP (governed by TP_MCS frequency) and downstream regions (dominated by convective intensity). (iii) The anomalous background environment, characterized by an enhanced upper-level westerly jets, cyclonic circulations over TP/Sichuan Basin, and enhanced low-level southerly moisture flux, drove frequent vacating of TP_MCSs in MY2020. These TP_MCSs, in turn, amplified the anomalous precipitation by intensifying upward motion through the release of latent heat from condensation. (iv) The key factors controlling the moving distance of TP_MCSs (particularly Type III) varied with their developmental stages. The potential for eastward propagation was primarily determined by Tibetan low-pressure systems, which enhanced the westerly steering flows. In contrast, the migration into the Yangtze River was largely dictated by southwest vortices, which intensified southerly winds that, in turn, drove enhanced moisture transport and convergence. These findings advance dynamical understanding of TP_MCS roles in extreme Mei-Yu rainfall and provide a benchmark for Yangtze River precipitation forecasting.