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<p>The diurnal variation of low-level winds serves as a primary modulator of nocturnal precipitation over the eastern slope of the Tibetan Plateau (ESTP). Utilizing Global Precipitation Measurement (GPM) rainfall products and the 5th generation of the European Centre for Medium-Range Weather Forecasts reanalysis (ERA5) data set from the summer months (June–August) of 2005–2023, this study classifies low-level circulations into different regimes based on the daily mean 850-hPa winds over the Sichuan Basin (SCB) and their diurnal amplitude. Focusing on two dominant regimes—strong daily mean wind with large diurnal amplitude (D+A+) and weak daily mean wind with small diurnal amplitude (D−A−)—we elucidate the thermodynamic and dynamic evolution of nocturnal rainfall. Our results demonstrate that D+A+ precipitation is positioned ahead of the steep western-to-northwestern slopes, propagates from west to northeast at night, and exhibits higher daily totals with a sharp midnight peak. D−A− precipitation is concentrated over the higher-elevation southwestern slopes, propagates from west to southeast during the night, and exhibits lower daily totals. Distinct spatial and temporal circulation characteristics emerge between these regimes: during D+A+ events, the development of a nocturnal low-level jet (LLJ) characterized by clockwise-rotating perturbation winds generates intense low-level convergence over the terrain transition zone. This mechanism facilitates the west-to-northward propagation of precipitation centers along the basin’s western flank, with peak intensity coinciding with LLJ establishment. D−A− events are driven by the intrusion of northern cold air, yielding anomalous northeasterlies and significant cold anomalies at 700&#xa0;hPa. In this regime, the cold air mass over the SCB mechanically lifts warm, moist southwesterly flow, causing the precipitation center to propagate southeastward. These findings underscore the important role of low-level circulation configurations in modulating nocturnal rainfall over complex topography and provide a refined framework for understanding precipitation mechanisms in the ESTP region.</p>

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Diurnal variation of the low tropospheric winds modulates nighttime precipitation processes over the eastern slope of the Tibetan Plateau

  • 期刊论文

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  • 发表日期：

    2026年7月10日

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  • Yang Hu,
  • Haoming Chen,
  • Juan Li,
  • Xuelin Hu

摘要

The diurnal variation of low-level winds serves as a primary modulator of nocturnal precipitation over the eastern slope of the Tibetan Plateau (ESTP). Utilizing Global Precipitation Measurement (GPM) rainfall products and the 5th generation of the European Centre for Medium-Range Weather Forecasts reanalysis (ERA5) data set from the summer months (June–August) of 2005–2023, this study classifies low-level circulations into different regimes based on the daily mean 850-hPa winds over the Sichuan Basin (SCB) and their diurnal amplitude. Focusing on two dominant regimes—strong daily mean wind with large diurnal amplitude (D+A+) and weak daily mean wind with small diurnal amplitude (D−A−)—we elucidate the thermodynamic and dynamic evolution of nocturnal rainfall. Our results demonstrate that D+A+ precipitation is positioned ahead of the steep western-to-northwestern slopes, propagates from west to northeast at night, and exhibits higher daily totals with a sharp midnight peak. D−A− precipitation is concentrated over the higher-elevation southwestern slopes, propagates from west to southeast during the night, and exhibits lower daily totals. Distinct spatial and temporal circulation characteristics emerge between these regimes: during D+A+ events, the development of a nocturnal low-level jet (LLJ) characterized by clockwise-rotating perturbation winds generates intense low-level convergence over the terrain transition zone. This mechanism facilitates the west-to-northward propagation of precipitation centers along the basin’s western flank, with peak intensity coinciding with LLJ establishment. D−A− events are driven by the intrusion of northern cold air, yielding anomalous northeasterlies and significant cold anomalies at 700 hPa. In this regime, the cold air mass over the SCB mechanically lifts warm, moist southwesterly flow, causing the precipitation center to propagate southeastward. These findings underscore the important role of low-level circulation configurations in modulating nocturnal rainfall over complex topography and provide a refined framework for understanding precipitation mechanisms in the ESTP region.