Diurnal variations of summer rainfall response to large-scale circulations and low-level winds over the Sichuan Basin
Diurnal variations of summer rainfall response to large-scale circulations and low-level winds over the Sichuan Basin
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DOI：
10.1007/s00382-023-07009-w
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发表时间：
2023-11
期刊：
影响因子：
4.6
通讯作者：
Juan Li;Haoming Chen;Xingwen Jiang;Puxi Li
中科院分区：
文献类型：
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作者：
Juan Li;Haoming Chen;Xingwen Jiang;Puxi Li
四川盆地夏季降水有明显的夜间峰值，这与夜间低空风的增强密切相关。利用2000 - 2020年6 - 8月21 a的IMERG降水产品和再分析资料，将低层风分为4类，即日平均风强或弱，日振幅大或小，以阐明它们对华南边界层降水的影响。结果表明：在日平均风场较强的情况下，西太平洋副热带高压的向西伸，决定了云贵高原东部的西南季风气流向偏南方向调整，为云贵高原东南侧的流域降水提供了丰富的暖湿气流资源。强的平均风，加上东风加速导致的较大的日变幅，加强了夜间水汽辐合，使华南边界层降水显著增加，并在午夜达到峰值。与此同时，SCB上空有明显的异常低层变暖，造成更不稳定的大气条件。此外，青藏高原东坡午后加热所产生的弱上升运动增强了东风，并促进了青藏高原西部夜间上升运动的发展，从而导致了降水日变幅的增大。相反，在日风较弱、日振幅较小的情况下，由于中纬度槽加深导致的较弱的水汽输送和冷却的行星边界层，以及白天TP东坡对流较活跃，降水受到抑制，日振幅较平缓。结果表明，与低空风日变化相关的大气条件是影响华南边界层降水和水汽收支的重要因素，傍晚低空风的强度可为华南边界层夜间降水的发展提供预报信号。
The evident nocturnal peak dominates the summer rainfall over the Sichuan Basin (SCB), which is closely related to the nocturnal intensification of low-level winds. Based on 21-year IMERG rainfall product and reanalysis data during summertime (June–August) from 2000 to 2020, the low-level winds are classified into four groups, with strong or weak daily mean wind accompanied by a large or small diurnal amplitude, to clarify their influences on rainfall over the SCB. The results show that under strong daily mean wind conditions, the westward extension of the Western Pacific Subtropical High (WPSH) determines the southwesterly monsoon airflow to be tuned to the southerly over the eastern Yunnan-Guizhou Plateau, which provides abundant warm and moist air resources for rainfall within the basin through the southeastern side of the SCB. Strong mean winds, coupled with a large diurnal amplitude due to the acceleration of easterly, strengthen the moisture convergence at night, and contribute to the rainfall increasing remarkable over the SCB with a peak at midnight. Meanwhile, there is an apparent anomalous low-level warming over the SCB, creating more unstable atmospheric conditions. In addition, the weak upward motion associated with the afternoon heating over the eastern slope of the Tibetan Plateau (TP) enhances the easterly and facilitates the development of upward motion over the western SCB in the early night, which is responsible for the larger diurnal amplitude of rainfall. On the contrary, rainfall is suppressed and the diurnal amplitude of rainfall is gentle under the condition of weak daily wind with small diurnal amplitude, due to the weak moisture transport and cooling planetary boundary layer related to the deepened midlatitude trough, as well as more active convection over the eastern slope of TP during the day. The results imply that atmospheric conditions associated with diurnal variation of low-level winds should be considered as a key component in regulating the rainfall and moisture budget over the SCB, the strength of low-level winds in the early evening may provide a predictive signal for the development of nocturnal rainfall over the SCB.