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<p>The Yungui Quasi-Stationary Front (YGQSF) is a front with quasi-north-south orientation and exhibits quasi-static characteristics at the daily scale. However, it has considerable diurnal variations, which exert significant influences on the local weather of southwestern China. Based on the ERA5 reanalysis data from 1984 to 2018, this study investigated the diurnal characteristics of YGQSF and the underlying thermodynamic mechanisms. Results reveal that the frontal diurnal variation mainly consists of two phases. (1) The YGQSF is observed to move eastward from 0800 to 1600 Beijing Time (BJT, UTC + 8) in correspondence with the intensification of shortwave radiation after sunrise. To the east of the front, where clouds persist throughout the day, these clouds modulate the near-surface shortwave radiation (about 50.3% of the cloudy/western side), contributing to an asymmetrical heating pattern between two sides of the front. This asymmetrical heating, centering to the east of the front line, favors the eastward movement of the front. (2) Conversely, the YGQSF shifts westward from 1600 to 0800 BJT when radiative cooling dominates. The presence of clouds in this scenario mitigates the radiative cooling over the eastern side, leading to an asymmetrical heating which weakens the temperature gradient across the frontal line. Consequently, the prevailing thermodynamic condition is insufficient to support the eastward frontal movement. Accompanied by intensification of easterly winds on the eastern side of the front, eventually favors the westward movement of the YGQSF.</p>

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Diurnal variations of Yungui quasi-stationary front and their relationship with cloud effect

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月25日

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  • Jiawei Zhang,
  • Jian Li,
  • Rucong Yu

摘要

The Yungui Quasi-Stationary Front (YGQSF) is a front with quasi-north-south orientation and exhibits quasi-static characteristics at the daily scale. However, it has considerable diurnal variations, which exert significant influences on the local weather of southwestern China. Based on the ERA5 reanalysis data from 1984 to 2018, this study investigated the diurnal characteristics of YGQSF and the underlying thermodynamic mechanisms. Results reveal that the frontal diurnal variation mainly consists of two phases. (1) The YGQSF is observed to move eastward from 0800 to 1600 Beijing Time (BJT, UTC + 8) in correspondence with the intensification of shortwave radiation after sunrise. To the east of the front, where clouds persist throughout the day, these clouds modulate the near-surface shortwave radiation (about 50.3% of the cloudy/western side), contributing to an asymmetrical heating pattern between two sides of the front. This asymmetrical heating, centering to the east of the front line, favors the eastward movement of the front. (2) Conversely, the YGQSF shifts westward from 1600 to 0800 BJT when radiative cooling dominates. The presence of clouds in this scenario mitigates the radiative cooling over the eastern side, leading to an asymmetrical heating which weakens the temperature gradient across the frontal line. Consequently, the prevailing thermodynamic condition is insufficient to support the eastward frontal movement. Accompanied by intensification of easterly winds on the eastern side of the front, eventually favors the westward movement of the YGQSF.