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<p>Precipitation diurnal variation is crucial for understanding the precipitation processes and improving the forecast skill of precipitation. In this study, the detailed features of precipitation diurnal variation over the middle and lower Yangtze River Basin in summer and associated mechanisms have been systematically revealed based on the high-resolution observational and reanalysis data of 1980 to 2022. The results show that the precipitation diurnal variation exhibits a distinct bimodal feature, with a primary peak occurring at 16:00–18:00 Beijing time (BJT) and a secondary peak concentrated around 07:00–09:00 BJT. Composite analysis of the three precipitation-day types (morning peak, afternoon peak, and dual-peak) reveals their fundamentally different environmental configurations: the morning type is dominated by nocturnal large-scale dynamic lifting that consumes pre-stored moisture; the afternoon type is governed by local thermal processes relying on daytime surface evaporation and energy storage; while the dual-peak type reflects the synergistic effect between dynamic forcing and thermal processes, with its morning peak driven by persistent dynamic convergence and its afternoon peak formed by thermal lifting that releases morning-accumulated energy. Spatially, cluster analysis identifies four characteristic patterns of precipitation diurnal variation: northwestern morning-dominant, mountainous afternoon-enhanced, transitional bimodal equilibrium, and southeastern coastal afternoon-dominant patterns. The differences among these patterns are primarily reflected in the afternoon peak precipitation (dominated by short- and medium-duration events). The spatial heterogeneity is primarily governed by thermally forced ascent: differential heating (mountain-plain and land-sea contrasts) generates upward motion, which is then intensified by topographic lifting, leading to strongly enhanced ascent and consequently higher afternoon precipitation in mountainous and coastal hilly areas. Furthermore, the study documents a distinct southeastward propagation delay of morning precipitation peaks within the 110°E–119°E and 28°N–30°N range, expanding understanding beyond the traditional paradigm of limited eastward propagation of morning precipitation. Sub-seasonal variation of the precipitation diurnal cycle shows a morning-to-afternoon transition, shifting from large-scale moisture transport dominance during the pre-Meiyu and Meiyu periods to thermal instability dominance in the post-Meiyu period.</p>

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Diurnal variation of summer precipitation in the middle and lower Yangtze River Basin and associated mechanisms

  • 期刊论文

  • 发表日期：

    2026年1月13日

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  • Xueqing Yuan,
  • Anning Huang,
  • Guangtao Dong,
  • Daokai Xue,
  • Xinsheng Zhu,
  • Rongchang Wu

摘要

Precipitation diurnal variation is crucial for understanding the precipitation processes and improving the forecast skill of precipitation. In this study, the detailed features of precipitation diurnal variation over the middle and lower Yangtze River Basin in summer and associated mechanisms have been systematically revealed based on the high-resolution observational and reanalysis data of 1980 to 2022. The results show that the precipitation diurnal variation exhibits a distinct bimodal feature, with a primary peak occurring at 16:00–18:00 Beijing time (BJT) and a secondary peak concentrated around 07:00–09:00 BJT. Composite analysis of the three precipitation-day types (morning peak, afternoon peak, and dual-peak) reveals their fundamentally different environmental configurations: the morning type is dominated by nocturnal large-scale dynamic lifting that consumes pre-stored moisture; the afternoon type is governed by local thermal processes relying on daytime surface evaporation and energy storage; while the dual-peak type reflects the synergistic effect between dynamic forcing and thermal processes, with its morning peak driven by persistent dynamic convergence and its afternoon peak formed by thermal lifting that releases morning-accumulated energy. Spatially, cluster analysis identifies four characteristic patterns of precipitation diurnal variation: northwestern morning-dominant, mountainous afternoon-enhanced, transitional bimodal equilibrium, and southeastern coastal afternoon-dominant patterns. The differences among these patterns are primarily reflected in the afternoon peak precipitation (dominated by short- and medium-duration events). The spatial heterogeneity is primarily governed by thermally forced ascent: differential heating (mountain-plain and land-sea contrasts) generates upward motion, which is then intensified by topographic lifting, leading to strongly enhanced ascent and consequently higher afternoon precipitation in mountainous and coastal hilly areas. Furthermore, the study documents a distinct southeastward propagation delay of morning precipitation peaks within the 110°E–119°E and 28°N–30°N range, expanding understanding beyond the traditional paradigm of limited eastward propagation of morning precipitation. Sub-seasonal variation of the precipitation diurnal cycle shows a morning-to-afternoon transition, shifting from large-scale moisture transport dominance during the pre-Meiyu and Meiyu periods to thermal instability dominance in the post-Meiyu period.