华南季风槽暴雨特征分析

利用NCEP再分析资料、地面观测资料和GDAS资料，对2018年8月27日—9月1日广东受季风低压影响发生的超历史极值、持续性特大暴雨天气过程的水汽输送特征进行了详细分析，同时利用Hysplit后向轨迹模式对水汽来源进行了诊断分析。结果表明：持续性特大暴雨过程期间，我国华南沿海为北半球的水汽汇合区，水汽主要来源于印度洋，经印度半岛北上至青藏高原南部向东转进入华南上空；另一部分水汽来源于西北太平洋和南海地区，三支水汽汇聚于华南上空，建立了稳定、持续的水汽输送通道，使得此次特大暴雨过程范围广、持续时间长。降水发生前期水汽辐合中心位于华南东部沿海，29日开始逐渐向西移动，于夜间达到峰值，水汽辐合最为明显，31日夜间其中心进一步西移并趋于减弱；水汽通量势函数高值区的变化与此次过程中降水峰值的逐日变化对应良好。逐日水汽辐合表现出明显的日变化特点，白天水汽辐合减弱，夜间明显加强，此次持续性特大暴雨过程呈现出季风降水特征。华南区域南边界是主要的水汽输入边界，且水汽输入主要集中在低层，尤其是华南中东部南边界的水汽输入量持续较高；29日夜间开始华南区域南边界的水汽输入量明显增大，30日达到最大，与大范围大暴雨和特大暴雨的区域及时段基本吻合。

The general circulation and water vapor balance over the Far East during the rainy season

Based on the NCEP reanalysis, conventional observation and Global Data Assimilation System (GDAS) data, the characteristics of water vapor transport were analyzed in a historically extreme event of persistent heavy rainstorm affected by a monsoon low pressure in Guangdong province from August 27 to September 1, 2018. Using the Hysplit backward trajectory model, the water vapor source was diagnosed. The results show that:(1) During the continuous heavy rainstorm, the southeast coast of China was the water vapor convergence area in northern hemisphere, and water vapor mainly came from the Indian Ocean, which then flowed northward from the Indian peninsula to the south of the Qinghai-Tibet Plateau, and then turned east into the south of China. Other portion of the water vapor came from the northwestern Pacific Ocean and the South China Sea. The three water vapor sources gathered in the South China and established a stable and continuous water vapor transport channel, which made the torrential rain process wide and lasted for a long time. (2) The water vapor convergence center in the early stage of precipitation occurred on the eastern coast of South China. On August 29th, its center gradually moved westward and the potential function averaged over Guangdong area reached the peak of the whole precipitation event at the night of 29th when the water vapor convergence was the most obvious. At the 31st night, the water vapor convergence center moved further westward and tended to weaken. The change of the high value of the water vapor flux potential function corresponded to the daily variation of precipitation peak during the torrential rain. (3) The daily water vapor convergence showed obvious daily variation. During the daytime, the water vapor convergence was weakened and obviously strengthened at the nighttime, showing the characteristics for monsoon precipitation. (4) The southern boundary of South China was the main water vapor input boundary and mainly concentrated in the lower layer, especially the water vapor input of the southeastern border of South China has been maintained at a high level. The water vapor input from the southern boundary of South China has been significantly increased from the night of 29th, and the whole layer's water vapor flux reached its maximum on the 30th, which was consistent with the area and time of the heavy rain.