8月高原季风对成都降水的影响研究

Study on the Influence of Plateau Monsoon on Precipitation in Chengdu in August

选取高时空分辨率的融合降水资料和ERA5再分析资料,研究8月高原季风影响成都降水的规律及物理机制。结果表明:成都8月降水量呈西高东低的分布特征;4个8月高原季风指数与同期成都降水均呈负相关,说明8月高原季风增强(减弱),对应同期成都降水减少(增多);两者的负相关性在8月中旬最强,表明这一时段高原季风对成都降水的影响最为显著;高原季风指数TPMI强年,西太副高偏南,孟加拉湾槽偏东较强,500 hPa距平场呈“+−”为主的经向分布,高原低压加强,四川东部上空受偏北气流影响,成都地区受下沉运动控制并且整层水汽辐散,对流稳定,不利于产生降水;TPMI弱年,西太副高偏北,孟加拉湾槽偏西较弱,500 hPa距平场呈“−+”为主的纬向分布,高原低压减弱,四川东部受偏南气流影响,有明显的水汽辐合且以上升运动为主,对流不稳定,利于产生降水。

Based on the fusion of precipitation data and ERA-5 reanalysis data,the law and physical mechanism of plateau monsoon affecting precipitation in Chengdu in August are studied.The results show that the precipitation in Chengdu in August is characterized by high in the west and low in the east.The four plateau monsoon indexes in Augusts are negatively correlated with the precipitation in Chengdu during the same period,indicating that the plateau monsoon increases(decreases)in August and the precipitation in Chengdu decreases(increases).The negative correlation is the strongest in mid-August,indicating that the plateau monsoon has the most significant impact on precipitation in Chengdu during this period.In the strong TPMI years,the Western Pacific Subtropical High is southerly,the Bay of Bengal trough is stronger easterly,the 500 hPa anomaly field is mainly distributed in the meridional direction of“+−”,the plateau low pressure is strengthened,and the east of Sichuan is affected by the northerly airflow.The Chengdu area is controlled by the sinking motion and the whole layer of water vapor divergence,the convection is stable,which is not conducive to precipitation.In weak years,the Western Pacific Subtropical High is to the north,the trough over the Bay of Bengal is to the west,the 500 hPa anomaly field is mainly zonal distribution of“−+”,the plateau low pressure is weakened,the eastern part of Sichuan is affected by the southerly airflow,there is obvious water vapor convergence and upward movement,the convection is not stable,which is conducive to produce precipitation.